22 Sep, 2016
1 commit
-
The SMP IPI struct descriptor is allocated on the stack except for the
workqueue and lockdep complains:INFO: trying to register non-static key.
the code is fine but needs lockdep annotation.
turning off the locking correctness validator.
CPU: 0 PID: 110 Comm: kworker/0:1 Not tainted 4.8.0-rc5+ #14
Hardware name: Dell Inc. Precision T3600/0PTTT9, BIOS A13 05/11/2014
Workqueue: events smp_call_on_cpu_callback
...
Call Trace:
dump_stack
register_lock_class
? __lock_acquire
__lock_acquire
? __lock_acquire
lock_acquire
? process_one_work
process_one_work
? process_one_work
worker_thread
? process_one_work
? process_one_work
kthread
? kthread_create_on_node
ret_from_forkSo allocate it on the stack too.
Signed-off-by: Peter Zijlstra (Intel)
[ Test and write commit message. ]
Signed-off-by: Borislav Petkov
Signed-off-by: Peter Zijlstra (Intel)
Cc: Linus Torvalds
Cc: Peter Zijlstra
Cc: Thomas Gleixner
Link: http://lkml.kernel.org/r/20160911084323.jhtnpb4b37t5tlno@pd.tnic
Signed-off-by: Ingo Molnar
05 Sep, 2016
2 commits
-
On some hardware models (e.g. Dell Studio 1555 laptop) some hardware
related functions (e.g. SMIs) are to be executed on physical CPU 0
only. Instead of open coding such a functionality multiple times in
the kernel add a service function for this purpose. This will enable
the possibility to take special measures in virtualized environments
like Xen, too.Signed-off-by: Juergen Gross
Signed-off-by: Peter Zijlstra (Intel)
Cc: Douglas_Warzecha@dell.com
Cc: Linus Torvalds
Cc: Peter Zijlstra
Cc: Thomas Gleixner
Cc: akataria@vmware.com
Cc: boris.ostrovsky@oracle.com
Cc: chrisw@sous-sol.org
Cc: david.vrabel@citrix.com
Cc: hpa@zytor.com
Cc: jdelvare@suse.com
Cc: jeremy@goop.org
Cc: linux@roeck-us.net
Cc: pali.rohar@gmail.com
Cc: rusty@rustcorp.com.au
Cc: virtualization@lists.linux-foundation.org
Cc: xen-devel@lists.xenproject.org
Link: http://lkml.kernel.org/r/1472453327-19050-4-git-send-email-jgross@suse.com
Signed-off-by: Ingo Molnar -
Add generic virtualization support for pinning the current vCPU to a
specified physical CPU. As this operation isn't performance critical
(a very limited set of operations like BIOS calls and SMIs is expected
to need this) just add a hypervisor specific indirection.Signed-off-by: Juergen Gross
Signed-off-by: Peter Zijlstra (Intel)
Cc: Douglas_Warzecha@dell.com
Cc: Linus Torvalds
Cc: Peter Zijlstra
Cc: Thomas Gleixner
Cc: akataria@vmware.com
Cc: boris.ostrovsky@oracle.com
Cc: chrisw@sous-sol.org
Cc: david.vrabel@citrix.com
Cc: hpa@zytor.com
Cc: jdelvare@suse.com
Cc: jeremy@goop.org
Cc: linux@roeck-us.net
Cc: pali.rohar@gmail.com
Cc: rusty@rustcorp.com.au
Cc: virtualization@lists.linux-foundation.org
Cc: xen-devel@lists.xenproject.org
Link: http://lkml.kernel.org/r/1472453327-19050-3-git-send-email-jgross@suse.com
Signed-off-by: Ingo Molnar
30 Jul, 2016
1 commit
-
Pull smp hotplug updates from Thomas Gleixner:
"This is the next part of the hotplug rework.- Convert all notifiers with a priority assigned
- Convert all CPU_STARTING/DYING notifiers
The final removal of the STARTING/DYING infrastructure will happen
when the merge window closes.Another 700 hundred line of unpenetrable maze gone :)"
* 'smp-hotplug-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (70 commits)
timers/core: Correct callback order during CPU hot plug
leds/trigger/cpu: Move from CPU_STARTING to ONLINE level
powerpc/numa: Convert to hotplug state machine
arm/perf: Fix hotplug state machine conversion
irqchip/armada: Avoid unused function warnings
ARC/time: Convert to hotplug state machine
clocksource/atlas7: Convert to hotplug state machine
clocksource/armada-370-xp: Convert to hotplug state machine
clocksource/exynos_mct: Convert to hotplug state machine
clocksource/arm_global_timer: Convert to hotplug state machine
rcu: Convert rcutree to hotplug state machine
KVM/arm/arm64/vgic-new: Convert to hotplug state machine
smp/cfd: Convert core to hotplug state machine
x86/x2apic: Convert to CPU hotplug state machine
profile: Convert to hotplug state machine
timers/core: Convert to hotplug state machine
hrtimer: Convert to hotplug state machine
x86/tboot: Convert to hotplug state machine
arm64/armv8 deprecated: Convert to hotplug state machine
hwtracing/coresight-etm4x: Convert to hotplug state machine
...
15 Jul, 2016
1 commit
-
Install the callbacks via the state machine. They are installed at runtime so
smpcfd_prepare_cpu() needs to be invoked by the boot-CPU.Signed-off-by: Richard Weinberger
[ Added the dropped CPU dying case back in. ]
Signed-off-by: Richard Cochran
Signed-off-by: Anna-Maria Gleixner
Reviewed-by: Sebastian Andrzej Siewior
Cc: Davidlohr Bueso
Cc: Linus Torvalds
Cc: Mel Gorman
Cc: Oleg Nesterov
Cc: Peter Zijlstra
Cc: Rasmus Villemoes
Cc: Thomas Gleixner
Cc: rt@linutronix.de
Link: http://lkml.kernel.org/r/20160713153337.818376366@linutronix.de
Signed-off-by: Ingo Molnar
14 Jun, 2016
1 commit
-
This new form allows using hardware assisted waiting.
Some hardware (ARM64 and x86) allow monitoring an address for changes,
so by providing a pointer we can use this to replace the cpu_relax()
with hardware optimized methods in the future.Requested-by: Will Deacon
Suggested-by: Linus Torvalds
Signed-off-by: Peter Zijlstra (Intel)
Cc: Andrew Morton
Cc: Paul E. McKenney
Cc: Peter Zijlstra
Cc: Thomas Gleixner
Signed-off-by: Ingo Molnar
16 Mar, 2016
1 commit
-
Pull cpu hotplug updates from Thomas Gleixner:
"This is the first part of the ongoing cpu hotplug rework:- Initial implementation of the state machine
- Runs all online and prepare down callbacks on the plugged cpu and
not on some random processor- Replaces busy loop waiting with completions
- Adds tracepoints so the states can be followed"
More detailed commentary on this work from an earlier email:
"What's wrong with the current cpu hotplug infrastructure?- Asymmetry
The hotplug notifier mechanism is asymmetric versus the bringup and
teardown. This is mostly caused by the notifier mechanism.- Largely undocumented dependencies
While some notifiers use explicitely defined notifier priorities,
we have quite some notifiers which use numerical priorities to
express dependencies without any documentation why.- Control processor driven
Most of the bringup/teardown of a cpu is driven by a control
processor. While it is understandable, that preperatory steps,
like idle thread creation, memory allocation for and initialization
of essential facilities needs to be done before a cpu can boot,
there is no reason why everything else must run on a control
processor. Before this patch series, bringup looks like this:Control CPU Booting CPU
do preparatory steps
kick cpu into lifedo low level init
sync with booting cpu sync with control cpu
bring the rest up
- All or nothing approach
There is no way to do partial bringups. That's something which is
really desired because we waste e.g. at boot substantial amount of
time just busy waiting that the cpu comes to life. That's stupid
as we could very well do preparatory steps and the initial IPI for
other cpus and then go back and do the necessary low level
synchronization with the freshly booted cpu.- Minimal debuggability
Due to the notifier based design, it's impossible to switch between
two stages of the bringup/teardown back and forth in order to test
the correctness. So in many hotplug notifiers the cancel
mechanisms are either not existant or completely untested.- Notifier [un]registering is tedious
To [un]register notifiers we need to protect against hotplug at
every callsite. There is no mechanism that bringup/teardown
callbacks are issued on the online cpus, so every caller needs to
do it itself. That also includes error rollback.What's the new design?
The base of the new design is a symmetric state machine, where both
the control processor and the booting/dying cpu execute a well
defined set of states. Each state is symmetric in the end, except
for some well defined exceptions, and the bringup/teardown can be
stopped and reversed at almost all states.So the bringup of a cpu will look like this in the future:
Control CPU Booting CPU
do preparatory steps
kick cpu into lifedo low level init
sync with booting cpu sync with control cpu
bring itself up
The synchronization step does not require the control cpu to wait.
That mechanism can be done asynchronously via a worker or some
other mechanism.The teardown can be made very similar, so that the dying cpu cleans
up and brings itself down. Cleanups which need to be done after
the cpu is gone, can be scheduled asynchronously as well.There is a long way to this, as we need to refactor the notion when a
cpu is available. Today we set the cpu online right after it comes
out of the low level bringup, which is not really correct.The proper mechanism is to set it to available, i.e. cpu local
threads, like softirqd, hotplug thread etc. can be scheduled on that
cpu, and once it finished all booting steps, it's set to online, so
general workloads can be scheduled on it. The reverse happens on
teardown. First thing to do is to forbid scheduling of general
workloads, then teardown all the per cpu resources and finally shut it
off completely.This patch series implements the basic infrastructure for this at the
core level. This includes the following:- Basic state machine implementation with well defined states, so
ordering and prioritization can be expressed.- Interfaces to [un]register state callbacks
This invokes the bringup/teardown callback on all online cpus with
the proper protection in place and [un]installs the callbacks in
the state machine array.For callbacks which have no particular ordering requirement we have
a dynamic state space, so that drivers don't have to register an
explicit hotplug state.If a callback fails, the code automatically does a rollback to the
previous state.- Sysfs interface to drive the state machine to a particular step.
This is only partially functional today. Full functionality and
therefor testability will be achieved once we converted all
existing hotplug notifiers over to the new scheme.- Run all CPU_ONLINE/DOWN_PREPARE notifiers on the booting/dying
processor:Control CPU Booting CPU
do preparatory steps
kick cpu into lifedo low level init
sync with booting cpu sync with control cpu
wait for boot
bring itself upSignal completion to control cpu
In a previous step of this work we've done a full tree mechanical
conversion of all hotplug notifiers to the new scheme. The balance
is a net removal of about 4000 lines of code.This is not included in this series, as we decided to take a
different approach. Instead of mechanically converting everything
over, we will do a proper overhaul of the usage sites one by one so
they nicely fit into the symmetric callback scheme.I decided to do that after I looked at the ugliness of some of the
converted sites and figured out that their hotplug mechanism is
completely buggered anyway. So there is no point to do a
mechanical conversion first as we need to go through the usage
sites one by one again in order to achieve a full symmetric and
testable behaviour"* 'smp-hotplug-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (23 commits)
cpu/hotplug: Document states better
cpu/hotplug: Fix smpboot thread ordering
cpu/hotplug: Remove redundant state check
cpu/hotplug: Plug death reporting race
rcu: Make CPU_DYING_IDLE an explicit call
cpu/hotplug: Make wait for dead cpu completion based
cpu/hotplug: Let upcoming cpu bring itself fully up
arch/hotplug: Call into idle with a proper state
cpu/hotplug: Move online calls to hotplugged cpu
cpu/hotplug: Create hotplug threads
cpu/hotplug: Split out the state walk into functions
cpu/hotplug: Unpark smpboot threads from the state machine
cpu/hotplug: Move scheduler cpu_online notifier to hotplug core
cpu/hotplug: Implement setup/removal interface
cpu/hotplug: Make target state writeable
cpu/hotplug: Add sysfs state interface
cpu/hotplug: Hand in target state to _cpu_up/down
cpu/hotplug: Convert the hotplugged cpu work to a state machine
cpu/hotplug: Convert to a state machine for the control processor
cpu/hotplug: Add tracepoints
...
10 Mar, 2016
2 commits
-
We can micro-optimize this call and mildly relax the
barrier requirements by relying on ctrl + rmb, keeping
the acquire semantics. In addition, this is pretty much
the now standard for busy-waiting under such restraints.Signed-off-by: Davidlohr Bueso
Acked-by: Peter Zijlstra (Intel)
Cc: Linus Torvalds
Cc: Peter Zijlstra
Cc: Thomas Gleixner
Cc: dave@stgolabs.net
Link: http://lkml.kernel.org/r/1457574936-19065-3-git-send-email-dbueso@suse.de
Signed-off-by: Ingo Molnar -
While the compiler tends to already to it for us (except for
csd_unlock), make it explicit. These helpers mainly deal with
the ->flags, are short-lived and can be called, for example,
from smp_call_function_many().Signed-off-by: Davidlohr Bueso
Acked-by: Peter Zijlstra (Intel)
Cc: Linus Torvalds
Cc: Peter Zijlstra
Cc: Thomas Gleixner
Cc: dave@stgolabs.net
Link: http://lkml.kernel.org/r/1457574936-19065-2-git-send-email-dbueso@suse.de
Signed-off-by: Ingo Molnar
02 Mar, 2016
1 commit
-
In order to let the hotplugged cpu take care of the setup/teardown, we need a
seperate hotplug thread.Signed-off-by: Thomas Gleixner
Cc: linux-arch@vger.kernel.org
Cc: Rik van Riel
Cc: Rafael Wysocki
Cc: "Srivatsa S. Bhat"
Cc: Peter Zijlstra
Cc: Arjan van de Ven
Cc: Sebastian Siewior
Cc: Rusty Russell
Cc: Steven Rostedt
Cc: Oleg Nesterov
Cc: Tejun Heo
Cc: Andrew Morton
Cc: Paul McKenney
Cc: Linus Torvalds
Cc: Paul Turner
Link: http://lkml.kernel.org/r/20160226182341.454541272@linutronix.de
Signed-off-by: Thomas Gleixner
07 Nov, 2015
1 commit
-
…d avoiding waking kswapd
__GFP_WAIT has been used to identify atomic context in callers that hold
spinlocks or are in interrupts. They are expected to be high priority and
have access one of two watermarks lower than "min" which can be referred
to as the "atomic reserve". __GFP_HIGH users get access to the first
lower watermark and can be called the "high priority reserve".Over time, callers had a requirement to not block when fallback options
were available. Some have abused __GFP_WAIT leading to a situation where
an optimisitic allocation with a fallback option can access atomic
reserves.This patch uses __GFP_ATOMIC to identify callers that are truely atomic,
cannot sleep and have no alternative. High priority users continue to use
__GFP_HIGH. __GFP_DIRECT_RECLAIM identifies callers that can sleep and
are willing to enter direct reclaim. __GFP_KSWAPD_RECLAIM to identify
callers that want to wake kswapd for background reclaim. __GFP_WAIT is
redefined as a caller that is willing to enter direct reclaim and wake
kswapd for background reclaim.This patch then converts a number of sites
o __GFP_ATOMIC is used by callers that are high priority and have memory
pools for those requests. GFP_ATOMIC uses this flag.o Callers that have a limited mempool to guarantee forward progress clear
__GFP_DIRECT_RECLAIM but keep __GFP_KSWAPD_RECLAIM. bio allocations fall
into this category where kswapd will still be woken but atomic reserves
are not used as there is a one-entry mempool to guarantee progress.o Callers that are checking if they are non-blocking should use the
helper gfpflags_allow_blocking() where possible. This is because
checking for __GFP_WAIT as was done historically now can trigger false
positives. Some exceptions like dm-crypt.c exist where the code intent
is clearer if __GFP_DIRECT_RECLAIM is used instead of the helper due to
flag manipulations.o Callers that built their own GFP flags instead of starting with GFP_KERNEL
and friends now also need to specify __GFP_KSWAPD_RECLAIM.The first key hazard to watch out for is callers that removed __GFP_WAIT
and was depending on access to atomic reserves for inconspicuous reasons.
In some cases it may be appropriate for them to use __GFP_HIGH.The second key hazard is callers that assembled their own combination of
GFP flags instead of starting with something like GFP_KERNEL. They may
now wish to specify __GFP_KSWAPD_RECLAIM. It's almost certainly harmless
if it's missed in most cases as other activity will wake kswapd.Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Christoph Lameter <cl@linux.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Vitaly Wool <vitalywool@gmail.com>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
20 Apr, 2015
1 commit
-
Commit 8053871d0f7f ("smp: Fix smp_call_function_single_async()
locking") fixed the locking for the asynchronous smp-call case, but in
the process of moving the lock handling around, one of the error cases
ended up not unlocking the call data at all.This went unnoticed on x86, because this is a "caller is buggy" case,
where the caller is trying to call a non-existent CPU. But apparently
ARM does that (at least under qemu-arm). Bindly doing cross-cpu calls
to random CPU's that aren't even online seems a bit fishy, but the error
handling was clearly not correct.Simply add the missing "csd_unlock()" to the error path.
Reported-and-tested-by: Guenter Roeck
Analyzed-by: Rabin Vincent
Acked-by: Ingo Molnar
Signed-off-by: Linus Torvalds
17 Apr, 2015
1 commit
-
The current smp_function_call code suffers a number of problems, most
notably smp_call_function_single_async() is broken.The problem is that flush_smp_call_function_queue() does csd_unlock()
_after_ calling csd->func(). This means that a caller cannot properly
synchronize the csd usage as it has to.Change the code to release the csd before calling ->func() for the
async case, and put a WARN_ON_ONCE(csd->flags & CSD_FLAG_LOCK) in
smp_call_function_single_async() to warn us of improper serialization,
because any waiting there can results in deadlocks when called with
IRQs disabled.Rename the (currently) unused WAIT flag to SYNCHRONOUS and (re)use it
such that we know what to do in flush_smp_call_function_queue().Rework csd_{,un}lock() to use smp_load_acquire() / smp_store_release()
to avoid some full barriers while more clearly providing lock
semantics.Finally move the csd maintenance out of generic_exec_single() into its
callers for clearer code.Signed-off-by: Linus Torvalds
[ Added changelog. ]
Signed-off-by: Peter Zijlstra (Intel)
Cc: Frederic Weisbecker
Cc: Jens Axboe
Cc: Rafael David Tinoco
Cc: Thomas Gleixner
Link: http://lkml.kernel.org/r/CA+55aFz492bzLFhdbKN-Hygjcreup7CjMEYk3nTSfRWjppz-OA@mail.gmail.com
Signed-off-by: Ingo Molnar
15 Oct, 2014
1 commit
-
Pull percpu consistent-ops changes from Tejun Heo:
"Way back, before the current percpu allocator was implemented, static
and dynamic percpu memory areas were allocated and handled separately
and had their own accessors. The distinction has been gone for many
years now; however, the now duplicate two sets of accessors remained
with the pointer based ones - this_cpu_*() - evolving various other
operations over time. During the process, we also accumulated other
inconsistent operations.This pull request contains Christoph's patches to clean up the
duplicate accessor situation. __get_cpu_var() uses are replaced with
with this_cpu_ptr() and __this_cpu_ptr() with raw_cpu_ptr().Unfortunately, the former sometimes is tricky thanks to C being a bit
messy with the distinction between lvalues and pointers, which led to
a rather ugly solution for cpumask_var_t involving the introduction of
this_cpu_cpumask_var_ptr().This converts most of the uses but not all. Christoph will follow up
with the remaining conversions in this merge window and hopefully
remove the obsolete accessors"* 'for-3.18-consistent-ops' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/percpu: (38 commits)
irqchip: Properly fetch the per cpu offset
percpu: Resolve ambiguities in __get_cpu_var/cpumask_var_t -fix
ia64: sn_nodepda cannot be assigned to after this_cpu conversion. Use __this_cpu_write.
percpu: Resolve ambiguities in __get_cpu_var/cpumask_var_t
Revert "powerpc: Replace __get_cpu_var uses"
percpu: Remove __this_cpu_ptr
clocksource: Replace __this_cpu_ptr with raw_cpu_ptr
sparc: Replace __get_cpu_var uses
avr32: Replace __get_cpu_var with __this_cpu_write
blackfin: Replace __get_cpu_var uses
tile: Use this_cpu_ptr() for hardware counters
tile: Replace __get_cpu_var uses
powerpc: Replace __get_cpu_var uses
alpha: Replace __get_cpu_var
ia64: Replace __get_cpu_var uses
s390: cio driver &__get_cpu_var replacements
s390: Replace __get_cpu_var uses
mips: Replace __get_cpu_var uses
MIPS: Replace __get_cpu_var uses in FPU emulator.
arm: Replace __this_cpu_ptr with raw_cpu_ptr
...
19 Sep, 2014
1 commit
-
Currently kick_all_cpus_sync() can break non-polling idle cpus
thru IPI interrupts.But sometimes we need to break the polling idle cpus immediately
to reselect the suitable c-state, also for non-idle cpus, we need
to do nothing if we try to wake up them.Here adding one new function wake_up_all_idle_cpus() to let all cpus
out of idle based on function wake_up_if_idle().Signed-off-by: Chuansheng Liu
Signed-off-by: Peter Zijlstra (Intel)
Cc: daniel.lezcano@linaro.org
Cc: rjw@rjwysocki.net
Cc: linux-pm@vger.kernel.org
Cc: changcheng.liu@intel.com
Cc: xiaoming.wang@intel.com
Cc: souvik.k.chakravarty@intel.com
Cc: luto@amacapital.net
Cc: Andrew Morton
Cc: Christoph Hellwig
Cc: Frederic Weisbecker
Cc: Geert Uytterhoeven
Cc: Jan Kara
Cc: Jens Axboe
Cc: Jens Axboe
Cc: Linus Torvalds
Cc: Michal Hocko
Cc: Paul Gortmaker
Cc: Roman Gushchin
Cc: Srivatsa S. Bhat
Link: http://lkml.kernel.org/r/1409815075-4180-2-git-send-email-chuansheng.liu@intel.com
Signed-off-by: Ingo Molnar
27 Aug, 2014
1 commit
-
Replace uses of __get_cpu_var for address calculation with this_cpu_ptr.
Cc: akpm@linux-foundation.org
Signed-off-by: Christoph Lameter
Signed-off-by: Tejun Heo
07 Aug, 2014
1 commit
-
The rarely-executed memry-allocation-failed callback path generates a
WARN_ON_ONCE() when smp_call_function_single() succeeds. Presumably
it's supposed to warn on failures.Signed-off-by: Sasha Levin
Cc: Christoph Lameter
Cc: Gilad Ben-Yossef
Cc: David Rientjes
Cc: Joonsoo Kim
Cc: Tejun Heo
Cc:
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds
16 Jul, 2014
1 commit
-
…ger tree-wide changes
Signed-off-by: Ingo Molnar <mingo@kernel.org>
24 Jun, 2014
1 commit
-
There is a race between the CPU offline code (within stop-machine) and
the smp-call-function code, which can lead to getting IPIs on the
outgoing CPU, *after* it has gone offline.Specifically, this can happen when using
smp_call_function_single_async() to send the IPI, since this API allows
sending asynchronous IPIs from IRQ disabled contexts. The exact race
condition is described below.During CPU offline, in stop-machine, we don't enforce any rule in the
_DISABLE_IRQ stage, regarding the order in which the outgoing CPU and
the other CPUs disable their local interrupts. Due to this, we can
encounter a situation in which an IPI is sent by one of the other CPUs
to the outgoing CPU (while it is *still* online), but the outgoing CPU
ends up noticing it only *after* it has gone offline.CPU 1 CPU 2
(Online CPU) (CPU going offline)Enter _PREPARE stage Enter _PREPARE stage
Enter _DISABLE_IRQ stage
=
Got a device interrupt, and | Didn't notice the IPI
the interrupt handler sent an | since interrupts were
IPI to CPU 2 using | disabled on this CPU.
smp_call_function_single_async() |
=Enter _DISABLE_IRQ stage
Enter _RUN stage Enter _RUN stage
=
Busy loop with interrupts | Invoke take_cpu_down()
disabled. | and take CPU 2 offline
=Enter _EXIT stage Enter _EXIT stage
Re-enable interrupts Re-enable interrupts
The pending IPI is noted
immediately, but alas,
the CPU is offline at
this point.This of course, makes the smp-call-function IPI handler code running on
CPU 2 unhappy and it complains about "receiving an IPI on an offline
CPU".One real example of the scenario on CPU 1 is the block layer's
complete-request call-path:__blk_complete_request() [interrupt-handler]
raise_blk_irq()
smp_call_function_single_async()However, if we look closely, the block layer does check that the target
CPU is online before firing the IPI. So in this case, it is actually
the unfortunate ordering/timing of events in the stop-machine phase that
leads to receiving IPIs after the target CPU has gone offline.In reality, getting a late IPI on an offline CPU is not too bad by
itself (this can happen even due to hardware latencies in IPI
send-receive). It is a bug only if the target CPU really went offline
without executing all the callbacks queued on its list. (Note that a
CPU is free to execute its pending smp-call-function callbacks in a
batch, without waiting for the corresponding IPIs to arrive for each one
of those callbacks).So, fixing this issue can be broken up into two parts:
1. Ensure that a CPU goes offline only after executing all the
callbacks queued on it.2. Modify the warning condition in the smp-call-function IPI handler
code such that it warns only if an offline CPU got an IPI *and* that
CPU had gone offline with callbacks still pending in its queue.Achieving part 1 is straight-forward - just flush (execute) all the
queued callbacks on the outgoing CPU in the CPU_DYING stage[1],
including those callbacks for which the source CPU's IPIs might not have
been received on the outgoing CPU yet. Once we do this, an IPI that
arrives late on the CPU going offline (either due to the race mentioned
above, or due to hardware latencies) will be completely harmless, since
the outgoing CPU would have executed all the queued callbacks before
going offline.Overall, this fix (parts 1 and 2 put together) additionally guarantees
that we will see a warning only when the *IPI-sender code* is buggy -
that is, if it queues the callback _after_ the target CPU has gone
offline.[1]. The CPU_DYING part needs a little more explanation: by the time we
execute the CPU_DYING notifier callbacks, the CPU would have already
been marked offline. But we want to flush out the pending callbacks at
this stage, ignoring the fact that the CPU is offline. So restructure
the IPI handler code so that we can by-pass the "is-cpu-offline?" check
in this particular case. (Of course, the right solution here is to fix
CPU hotplug to mark the CPU offline _after_ invoking the CPU_DYING
notifiers, but this requires a lot of audit to ensure that this change
doesn't break any existing code; hence lets go with the solution
proposed above until that is done).[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: Srivatsa S. Bhat
Suggested-by: Frederic Weisbecker
Cc: "Paul E. McKenney"
Cc: Borislav Petkov
Cc: Christoph Hellwig
Cc: Frederic Weisbecker
Cc: Gautham R Shenoy
Cc: Ingo Molnar
Cc: Mel Gorman
Cc: Mike Galbraith
Cc: Oleg Nesterov
Cc: Peter Zijlstra
Cc: Rafael J. Wysocki
Cc: Rik van Riel
Cc: Rusty Russell
Cc: Steven Rostedt
Cc: Tejun Heo
Cc: Thomas Gleixner
Tested-by: Sachin Kamat
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds
16 Jun, 2014
1 commit
-
irq work currently only supports local callbacks. However its code
is mostly ready to run remote callbacks and we have some potential user.The full nohz subsystem currently open codes its own remote irq work
on top of the scheduler ipi when it wants a CPU to reevaluate its next
tick. However this ad hoc solution bloats the scheduler IPI.Lets just extend the irq work subsystem to support remote queuing on top
of the generic SMP IPI to handle this kind of user. This shouldn't add
noticeable overhead.Suggested-by: Peter Zijlstra
Acked-by: Peter Zijlstra
Cc: Andrew Morton
Cc: Eric Dumazet
Cc: Ingo Molnar
Cc: Kevin Hilman
Cc: Paul E. McKenney
Cc: Peter Zijlstra
Cc: Thomas Gleixner
Cc: Viresh Kumar
Signed-off-by: Frederic Weisbecker
07 Jun, 2014
1 commit
-
There is a longstanding problem related to CPU hotplug which causes IPIs
to be delivered to offline CPUs, and the smp-call-function IPI handler
code prints out a warning whenever this is detected. Every once in a
while this (usually harmless) warning gets reported on LKML, but so far
it has not been completely fixed. Usually the solution involves finding
out the IPI sender and fixing it by adding appropriate synchronization
with CPU hotplug.However, while going through one such internal bug reports, I found that
there is a significant bug in the receiver side itself (more
specifically, in stop-machine) that can lead to this problem even when
the sender code is perfectly fine. This patchset fixes that
synchronization problem in the CPU hotplug stop-machine code.Patch 1 adds some additional debug code to the smp-call-function
framework, to help debug such issues easily.Patch 2 modifies the stop-machine code to ensure that any IPIs that were
sent while the target CPU was online, would be noticed and handled by
that CPU without fail before it goes offline. Thus, this avoids
scenarios where IPIs are received on offline CPUs (as long as the sender
uses proper hotplug synchronization).In fact, I debugged the problem by using Patch 1, and found that the
payload of the IPI was always the block layer's trigger_softirq()
function. But I was not able to find anything wrong with the block
layer code. That's when I started looking at the stop-machine code and
realized that there is a race-window which makes the IPI _receiver_ the
culprit, not the sender. Patch 2 fixes that race and hence this should
put an end to most of the hard-to-debug IPI-to-offline-CPU issues.This patch (of 2):
Today the smp-call-function code just prints a warning if we get an IPI
on an offline CPU. This info is sufficient to let us know that
something went wrong, but often it is very hard to debug exactly who
sent the IPI and why, from this info alone.In most cases, we get the warning about the IPI to an offline CPU,
immediately after the CPU going offline comes out of the stop-machine
phase and reenables interrupts. Since all online CPUs participate in
stop-machine, the information regarding the sender of the IPI is already
lost by the time we exit the stop-machine loop. So even if we dump the
stack on each CPU at this point, we won't find anything useful since all
of them will show the stack-trace of the stopper thread. So we need a
better way to figure out who sent the IPI and why.To achieve this, when we detect an IPI targeted to an offline CPU, loop
through the call-single-data linked list and print out the payload
(i.e., the name of the function which was supposed to be executed by the
target CPU). This would give us an insight as to who might have sent
the IPI and help us debug this further.[akpm@linux-foundation.org: correctly suppress warning output on second and later occurrences]
Signed-off-by: Srivatsa S. Bhat
Cc: Peter Zijlstra
Cc: Thomas Gleixner
Cc: Ingo Molnar
Cc: Tejun Heo
Cc: Rusty Russell
Cc: Frederic Weisbecker
Cc: Christoph Hellwig
Cc: Mel Gorman
Cc: Rik van Riel
Cc: Borislav Petkov
Cc: Steven Rostedt
Cc: Mike Galbraith
Cc: Gautham R Shenoy
Cc: "Paul E. McKenney"
Cc: Oleg Nesterov
Cc: Rafael J. Wysocki
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds
25 Feb, 2014
6 commits
-
The name __smp_call_function_single() doesn't tell much about the
properties of this function, especially when compared to
smp_call_function_single().The comments above the implementation are also misleading. The main
point of this function is actually not to be able to embed the csd
in an object. This is actually a requirement that result from the
purpose of this function which is to raise an IPI asynchronously.As such it can be called with interrupts disabled. And this feature
comes at the cost of the caller who then needs to serialize the
IPIs on this csd.Lets rename the function and enhance the comments so that they reflect
these properties.Suggested-by: Christoph Hellwig
Cc: Andrew Morton
Cc: Christoph Hellwig
Cc: Ingo Molnar
Cc: Jan Kara
Cc: Jens Axboe
Signed-off-by: Frederic Weisbecker
Signed-off-by: Jens Axboe -
The main point of calling __smp_call_function_single() is to send
an IPI in a pure asynchronous way. By embedding a csd in an object,
a caller can send the IPI without waiting for a previous one to complete
as is required by smp_call_function_single() for example. As such,
sending this kind of IPI can be safe even when irqs are disabled.This flexibility comes at the expense of the caller who then needs to
synchronize the csd lifecycle by himself and make sure that IPIs on a
single csd are serialized.This is how __smp_call_function_single() works when wait = 0 and this
usecase is relevant.Now there don't seem to be any usecase with wait = 1 that can't be
covered by smp_call_function_single() instead, which is safer. Lets look
at the two possible scenario:1) The user calls __smp_call_function_single(wait = 1) on a csd embedded
in an object. It looks like a nice and convenient pattern at the first
sight because we can then retrieve the object from the IPI handler easily.But actually it is a waste of memory space in the object since the csd
can be allocated from the stack by smp_call_function_single(wait = 1)
and the object can be passed an the IPI argument.Besides that, embedding the csd in an object is more error prone
because the caller must take care of the serialization of the IPIs
for this csd.2) The user calls __smp_call_function_single(wait = 1) on a csd that
is allocated on the stack. It's ok but smp_call_function_single()
can do it as well and it already takes care of the allocation on the
stack. Again it's more simple and less error prone.Therefore, using the underscore prepend API version with wait = 1
is a bad pattern and a sign that the caller can do safer and more
simple.There was a single user of that which has just been converted.
So lets remove this option to discourage further users.Cc: Andrew Morton
Cc: Christoph Hellwig
Cc: Ingo Molnar
Cc: Jan Kara
Cc: Jens Axboe
Signed-off-by: Frederic Weisbecker
Signed-off-by: Jens Axboe -
Move this function closer to __smp_call_function_single(). These functions
have very similar behavior and should be displayed in the same block
for clarity.Reviewed-by: Jan Kara
Cc: Andrew Morton
Cc: Christoph Hellwig
Cc: Ingo Molnar
Cc: Jan Kara
Cc: Jens Axboe
Signed-off-by: Frederic Weisbecker
Signed-off-by: Jens Axboe -
__smp_call_function_single() and smp_call_function_single() share some
code that can be factorized: execute inline when the target is local,
check if the target is online, lock the csd, call generic_exec_single().Lets move the common parts to generic_exec_single().
Reviewed-by: Jan Kara
Cc: Andrew Morton
Cc: Christoph Hellwig
Cc: Ingo Molnar
Cc: Jan Kara
Cc: Jens Axboe
Signed-off-by: Frederic Weisbecker
Signed-off-by: Jens Axboe -
Align __smp_call_function_single() with smp_call_function_single() so
that it also checks whether requested cpu is still online.Signed-off-by: Jan Kara
Cc: Andrew Morton
Cc: Christoph Hellwig
Cc: Ingo Molnar
Cc: Jens Axboe
Signed-off-by: Frederic Weisbecker
Signed-off-by: Jens Axboe -
The IPI function llist iteration is open coded. Lets simplify this
with using an llist iterator.Also we want to keep the iteration safe against possible
csd.llist->next value reuse from the IPI handler. At least the block
subsystem used to do such things so lets stay careful and use
llist_for_each_entry_safe().Signed-off-by: Jan Kara
Cc: Andrew Morton
Cc: Christoph Hellwig
Cc: Ingo Molnar
Cc: Jens Axboe
Signed-off-by: Frederic Weisbecker
Signed-off-by: Jens Axboe
31 Jan, 2014
2 commits
-
After commit 9a46ad6d6df3 ("smp: make smp_call_function_many() use logic
similar to smp_call_function_single()"), cfd->cpumask is accessed only
in smp_call_function_many(). So there is no more need to copy it into
cfd->cpumask_ipi before putting csd into the list. The cpumask_ipi
field is obsolete and can be removed.Signed-off-by: Roman Gushchin
Cc: Ingo Molnar
Cc: Christoph Hellwig
Cc: Wang YanQing
Cc: Xie XiuQi
Cc: Shaohua Li
Cc: Peter Zijlstra
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds -
Make smp_call_function_single and friends more efficient by using a
lockless list.Signed-off-by: Christoph Hellwig
Reviewed-by: Jan Kara
Cc: Jens Axboe
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds
15 Nov, 2013
2 commits
-
Signed-off-by: Christoph Hellwig
Cc: Jan Kara
Cc: Jens Axboe
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds -
We've switched over every architecture that supports SMP to it, so
remove the new useless config variable.Signed-off-by: Christoph Hellwig
Cc: Jan Kara
Cc: Jens Axboe
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds
14 Nov, 2013
1 commit
-
Pull block IO core updates from Jens Axboe:
"This is the pull request for the core changes in the block layer for
3.13. It contains:- The new blk-mq request interface.
This is a new and more scalable queueing model that marries the
best part of the request based interface we currently have (which
is fully featured, but scales poorly) and the bio based "interface"
which the new drivers for high IOPS devices end up using because
it's much faster than the request based one.The bio interface has no block layer support, since it taps into
the stack much earlier. This means that drivers end up having to
implement a lot of functionality on their own, like tagging,
timeout handling, requeue, etc. The blk-mq interface provides all
these. Some drivers even provide a switch to select bio or rq and
has code to handle both, since things like merging only works in
the rq model and hence is faster for some workloads. This is a
huge mess. Conversion of these drivers nets us a substantial code
reduction. Initial results on converting SCSI to this model even
shows an 8x improvement on single queue devices. So while the
model was intended to work on the newer multiqueue devices, it has
substantial improvements for "classic" hardware as well. This code
has gone through extensive testing and development, it's now ready
to go. A pull request is coming to convert virtio-blk to this
model will be will be coming as well, with more drivers scheduled
for 3.14 conversion.- Two blktrace fixes from Jan and Chen Gang.
- A plug merge fix from Alireza Haghdoost.
- Conversion of __get_cpu_var() from Christoph Lameter.
- Fix for sector_div() with 64-bit divider from Geert Uytterhoeven.
- A fix for a race between request completion and the timeout
handling from Jeff Moyer. This is what caused the merge conflict
with blk-mq/core, in case you are looking at that.- A dm stacking fix from Mike Snitzer.
- A code consolidation fix and duplicated code removal from Kent
Overstreet.- A handful of block bug fixes from Mikulas Patocka, fixing a loop
crash and memory corruption on blk cg.- Elevator switch bug fix from Tomoki Sekiyama.
A heads-up that I had to rebase this branch. Initially the immutable
bio_vecs had been queued up for inclusion, but a week later, it became
clear that it wasn't fully cooked yet. So the decision was made to
pull this out and postpone it until 3.14. It was a straight forward
rebase, just pruning out the immutable series and the later fixes of
problems with it. The rest of the patches applied directly and no
further changes were made"* 'for-3.13/core' of git://git.kernel.dk/linux-block: (31 commits)
block: replace IS_ERR and PTR_ERR with PTR_ERR_OR_ZERO
block: replace IS_ERR and PTR_ERR with PTR_ERR_OR_ZERO
block: Do not call sector_div() with a 64-bit divisor
kernel: trace: blktrace: remove redundent memcpy() in compat_blk_trace_setup()
block: Consolidate duplicated bio_trim() implementations
block: Use rw_copy_check_uvector()
block: Enable sysfs nomerge control for I/O requests in the plug list
block: properly stack underlying max_segment_size to DM device
elevator: acquire q->sysfs_lock in elevator_change()
elevator: Fix a race in elevator switching and md device initialization
block: Replace __get_cpu_var uses
bdi: test bdi_init failure
block: fix a probe argument to blk_register_region
loop: fix crash if blk_alloc_queue fails
blk-core: Fix memory corruption if blkcg_init_queue fails
block: fix race between request completion and timeout handling
blktrace: Send BLK_TN_PROCESS events to all running traces
blk-mq: don't disallow request merges for req->special being set
blk-mq: mq plug list breakage
blk-mq: fix for flush deadlock
...
25 Oct, 2013
2 commits
-
blk-mq reuses the request potentially immediately, since the most
cache hot is always given out first. This means that rq->csd could
be reused between csd->func() being called and csd_unlock() being
called. This isn't a problem, since we never use wait == 1 for
the smp call function. Add CSD_FLAG_WAIT to be able to tell the
difference, retaining the warning for other cases.Cc: Ingo Molnar
Signed-off-by: Jens Axboe -
The blk-mq core and the blk-mq null driver uses it.
Reviewed-by: Christoph Hellwig
Acked-by: Ingo Molnar
Signed-off-by: Jens Axboe
01 Oct, 2013
1 commit
-
Turn it into (for example):
[ 0.073380] x86: Booting SMP configuration:
[ 0.074005] .... node #0, CPUs: #1 #2 #3 #4 #5 #6 #7
[ 0.603005] .... node #1, CPUs: #8 #9 #10 #11 #12 #13 #14 #15
[ 1.200005] .... node #2, CPUs: #16 #17 #18 #19 #20 #21 #22 #23
[ 1.796005] .... node #3, CPUs: #24 #25 #26 #27 #28 #29 #30 #31
[ 2.393005] .... node #4, CPUs: #32 #33 #34 #35 #36 #37 #38 #39
[ 2.996005] .... node #5, CPUs: #40 #41 #42 #43 #44 #45 #46 #47
[ 3.600005] .... node #6, CPUs: #48 #49 #50 #51 #52 #53 #54 #55
[ 4.202005] .... node #7, CPUs: #56 #57 #58 #59 #60 #61 #62 #63
[ 4.811005] .... node #8, CPUs: #64 #65 #66 #67 #68 #69 #70 #71
[ 5.421006] .... node #9, CPUs: #72 #73 #74 #75 #76 #77 #78 #79
[ 6.032005] .... node #10, CPUs: #80 #81 #82 #83 #84 #85 #86 #87
[ 6.648006] .... node #11, CPUs: #88 #89 #90 #91 #92 #93 #94 #95
[ 7.262005] .... node #12, CPUs: #96 #97 #98 #99 #100 #101 #102 #103
[ 7.865005] .... node #13, CPUs: #104 #105 #106 #107 #108 #109 #110 #111
[ 8.466005] .... node #14, CPUs: #112 #113 #114 #115 #116 #117 #118 #119
[ 9.073006] .... node #15, CPUs: #120 #121 #122 #123 #124 #125 #126 #127
[ 9.679901] x86: Booted up 16 nodes, 128 CPUsand drop useless elements.
Change num_digits() to hpa's division-avoiding, cell-phone-typed
version which he went at great lengths and pains to submit on a
Saturday evening.Signed-off-by: Borislav Petkov
Cc: huawei.libin@huawei.com
Cc: wangyijing@huawei.com
Cc: fenghua.yu@intel.com
Cc: guohanjun@huawei.com
Cc: paul.gortmaker@windriver.com
Cc: Linus Torvalds
Cc: Andrew Morton
Cc: Peter Zijlstra
Cc: Thomas Gleixner
Link: http://lkml.kernel.org/r/20130930095624.GB16383@pd.tnic
Signed-off-by: Ingo Molnar
12 Sep, 2013
2 commits
-
As in commit f21afc25f9ed ("smp.h: Use local_irq_{save,restore}() in
!SMP version of on_each_cpu()"), we don't want to enable irqs if they
are not already enabled.I don't know of any bugs currently caused by this unconditional
local_irq_enable(), but I want to use this function in MIPS/OCTEON early
boot (when we have early_boot_irqs_disabled). This also makes this
function have similar semantics to on_each_cpu() which is good in
itself.Signed-off-by: David Daney
Cc: Gilad Ben-Yossef
Cc: Christoph Lameter
Cc: Chris Metcalf
Cc: Peter Zijlstra
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds -
When failure occurs in hotplug_cfd(), need release related resources, or
will cause memory leak.Signed-off-by: Chen Gang
Acked-by: Wang YanQing
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds
04 Sep, 2013
1 commit
-
Pull scheduler changes from Ingo Molnar:
"Various optimizations, cleanups and smaller fixes - no major changes
in scheduler behavior"* 'sched-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
sched/fair: Fix the sd_parent_degenerate() code
sched/fair: Rework and comment the group_imb code
sched/fair: Optimize find_busiest_queue()
sched/fair: Make group power more consistent
sched/fair: Remove duplicate load_per_task computations
sched/fair: Shrink sg_lb_stats and play memset games
sched: Clean-up struct sd_lb_stat
sched: Factor out code to should_we_balance()
sched: Remove one division operation in find_busiest_queue()
sched/cputime: Use this_cpu_add() in task_group_account_field()
cpumask: Fix cpumask leak in partition_sched_domains()
sched/x86: Optimize switch_mm() for multi-threaded workloads
generic-ipi: Kill unnecessary variable - csd_flags
numa: Mark __node_set() as __always_inline
sched/fair: Cleanup: remove duplicate variable declaration
sched/__wake_up_sync_key(): Fix nr_exclusive tasks which lead to WF_SYNC clearing
19 Aug, 2013
1 commit
-
Fix locking description: after commit 8969a5ede0f9e17da4b9437
("generic-ipi: remove kmalloc()"), wait = 0 can be guaranteed
because we don't kmalloc() anymore.Signed-off-by: Xie XiuQi
Cc: Sheng Yang
Cc: Peter Zijlstra
Cc: Jens Axboe
Cc: Rusty Russell
Link: http://lkml.kernel.org/r/51F5E6F8.1000801@huawei.com
Signed-off-by: Ingo Molnar
31 Jul, 2013
1 commit
-
After commit 8969a5ede0f9e17da4b943712429aef2c9bcd82b
("generic-ipi: remove kmalloc()"), wait = 0 can be guaranteed,
and all callsites of generic_exec_single() do an unconditional
csd_lock() now.So csd_flags is unnecessary now. Remove it.
Signed-off-by: Xie XiuQi
Signed-off-by: Peter Zijlstra
Cc: Oleg Nesterov
Cc: Linus Torvalds
Cc: Nick Piggin
Cc: Jens Axboe
Cc: "Paul E. McKenney"
Cc: Rusty Russell
Link: http://lkml.kernel.org/r/51F72DA1.7010401@huawei.com
Signed-off-by: Ingo Molnar