26 Jan, 2017
2 commits
-
commit 52d7e48b86fc108e45a656d8e53e4237993c481d upstream.
The current preemptible RCU implementation goes through three phases
during bootup. In the first phase, there is only one CPU that is running
with preemption disabled, so that a no-op is a synchronous grace period.
In the second mid-boot phase, the scheduler is running, but RCU has
not yet gotten its kthreads spawned (and, for expedited grace periods,
workqueues are not yet running. During this time, any attempt to do
a synchronous grace period will hang the system (or complain bitterly,
depending). In the third and final phase, RCU is fully operational and
everything works normally.This has been OK for some time, but there has recently been some
synchronous grace periods showing up during the second mid-boot phase.
This code worked "by accident" for awhile, but started failing as soon
as expedited RCU grace periods switched over to workqueues in commit
8b355e3bc140 ("rcu: Drive expedited grace periods from workqueue").
Note that the code was buggy even before this commit, as it was subject
to failure on real-time systems that forced all expedited grace periods
to run as normal grace periods (for example, using the rcu_normal ksysfs
parameter). The callchain from the failure case is as follows:early_amd_iommu_init()
|-> acpi_put_table(ivrs_base);
|-> acpi_tb_put_table(table_desc);
|-> acpi_tb_invalidate_table(table_desc);
|-> acpi_tb_release_table(...)
|-> acpi_os_unmap_memory
|-> acpi_os_unmap_iomem
|-> acpi_os_map_cleanup
|-> synchronize_rcu_expeditedThe kernel showing this callchain was built with CONFIG_PREEMPT_RCU=y,
which caused the code to try using workqueues before they were
initialized, which did not go well.This commit therefore reworks RCU to permit synchronous grace periods
to proceed during this mid-boot phase. This commit is therefore a
fix to a regression introduced in v4.9, and is therefore being put
forward post-merge-window in v4.10.This commit sets a flag from the existing rcu_scheduler_starting()
function which causes all synchronous grace periods to take the expedited
path. The expedited path now checks this flag, using the requesting task
to drive the expedited grace period forward during the mid-boot phase.
Finally, this flag is updated by a core_initcall() function named
rcu_exp_runtime_mode(), which causes the runtime codepaths to be used.Note that this arrangement assumes that tasks are not sent POSIX signals
(or anything similar) from the time that the first task is spawned
through core_initcall() time.Fixes: 8b355e3bc140 ("rcu: Drive expedited grace periods from workqueue")
Reported-by: "Zheng, Lv"
Reported-by: Borislav Petkov
Signed-off-by: Paul E. McKenney
Tested-by: Stan Kain
Tested-by: Ivan
Tested-by: Emanuel Castelo
Tested-by: Bruno Pesavento
Tested-by: Borislav Petkov
Tested-by: Frederic Bezies
Signed-off-by: Greg Kroah-Hartman -
commit f466ae66fa6a599f9a53b5f9bafea4b8cfffa7fb upstream.
It is now legal to invoke synchronize_sched() at early boot, which causes
Tiny RCU's synchronize_sched() to emit spurious splats. This commit
therefore removes the cond_resched() from Tiny RCU's synchronize_sched().Fixes: 8b355e3bc140 ("rcu: Drive expedited grace periods from workqueue")
Signed-off-by: Paul E. McKenney
Signed-off-by: Greg Kroah-Hartman
16 Oct, 2016
1 commit
-
Pull gcc plugins update from Kees Cook:
"This adds a new gcc plugin named "latent_entropy". It is designed to
extract as much possible uncertainty from a running system at boot
time as possible, hoping to capitalize on any possible variation in
CPU operation (due to runtime data differences, hardware differences,
SMP ordering, thermal timing variation, cache behavior, etc).At the very least, this plugin is a much more comprehensive example
for how to manipulate kernel code using the gcc plugin internals"* tag 'gcc-plugins-v4.9-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux:
latent_entropy: Mark functions with __latent_entropy
gcc-plugins: Add latent_entropy plugin
11 Oct, 2016
1 commit
-
The __latent_entropy gcc attribute can be used only on functions and
variables. If it is on a function then the plugin will instrument it for
gathering control-flow entropy. If the attribute is on a variable then
the plugin will initialize it with random contents. The variable must
be an integer, an integer array type or a structure with integer fields.These specific functions have been selected because they are init
functions (to help gather boot-time entropy), are called at unpredictable
times, or they have variable loops, each of which provide some level of
latent entropy.Signed-off-by: Emese Revfy
[kees: expanded commit message]
Signed-off-by: Kees Cook
04 Oct, 2016
1 commit
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Pull locking updates from Ingo Molnar:
"The main changes in this cycle were:- rwsem micro-optimizations (Davidlohr Bueso)
- Improve the implementation and optimize the performance of
percpu-rwsems. (Peter Zijlstra.)- Convert all lglock users to better facilities such as percpu-rwsems
or percpu-spinlocks and remove lglocks. (Peter Zijlstra)- Remove the ticket (spin)lock implementation. (Peter Zijlstra)
- Korean translation of memory-barriers.txt and related fixes to the
English document. (SeongJae Park)- misc fixes and cleanups"
* 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (24 commits)
x86/cmpxchg, locking/atomics: Remove superfluous definitions
x86, locking/spinlocks: Remove ticket (spin)lock implementation
locking/lglock: Remove lglock implementation
stop_machine: Remove stop_cpus_lock and lg_double_lock/unlock()
fs/locks: Use percpu_down_read_preempt_disable()
locking/percpu-rwsem: Add down_read_preempt_disable()
fs/locks: Replace lg_local with a per-cpu spinlock
fs/locks: Replace lg_global with a percpu-rwsem
locking/percpu-rwsem: Add DEFINE_STATIC_PERCPU_RWSEMand percpu_rwsem_assert_held()
locking/pv-qspinlock: Use cmpxchg_release() in __pv_queued_spin_unlock()
locking/rwsem, x86: Drop a bogus cc clobber
futex: Add some more function commentry
locking/hung_task: Show all locks
locking/rwsem: Scan the wait_list for readers only once
locking/rwsem: Remove a few useless comments
locking/rwsem: Return void in __rwsem_mark_wake()
locking, rcu, cgroup: Avoid synchronize_sched() in __cgroup_procs_write()
locking/Documentation: Add Korean translation
locking/Documentation: Fix a typo of example result
locking/Documentation: Fix wrong section reference
...
15 Sep, 2016
1 commit
-
…ug.2016.08.22c' and 'torture.2016.08.22c' into HEAD
doc.2016.08.22c: Documentation updates
exp.2016.08.22c: Expedited grace-period updates
fixes.2016.09.14a: Miscellaneous fixes
hotplug.2016.08.22c: CPU-hotplug changes
torture.2016.08.22c: Torture-test changes
23 Aug, 2016
14 commits
-
A few rcuperf dmesg output messages have no space between the flag and
the start of the message. In contrast, every other messages consistently
supplies a single space. This difference makes rcuperf dmesg output
hard to read and to mechanically parse. This commit therefore fixes
this problem by modifying a pr_alert() call and PERFOUT_STRING() macro
function to provide that single space.Signed-off-by: SeongJae Park
Signed-off-by: Paul E. McKenney -
Tests for rcu_barrier() were introduced by commit fae4b54f28f0 ("rcu:
Introduce rcutorture testing for rcu_barrier()"). This commit updated
the documentation to say that the "rtbe" field in rcutorture's dmesg
output indicates test failure. However, the code was not updated, only
the documentation. This commit therefore updates the code to match the
updated documentation.Signed-off-by: SeongJae Park
Signed-off-by: Paul E. McKenney -
This commit adds a dump of the scheduler state for stalled rcutorture
writer tasks. This addition provides yet more debug for the intermittent
"failures to proceed", where grace periods move ahead but the rcutorture
writer tasks fail to do so.Signed-off-by: Paul E. McKenney
-
Install the callbacks via the state machine and let the core invoke
the callbacks on the already online CPUs.Cc: Josh Triplett
Cc: "Paul E. McKenney"
Cc: Steven Rostedt
Cc: Mathieu Desnoyers
Cc: Lai Jiangshan
Signed-off-by: Sebastian Andrzej Siewior
Signed-off-by: Paul E. McKenney -
Up to now, RCU has assumed that the CPU-online process makes it from
CPU_UP_PREPARE to set_cpu_online() within one jiffy. Given the recent
rise of virtualized environments, this assumption is very clearly
obsolete. Failing to meet this deadline can result in RCU paying
attention to an incoming CPU for one jiffy, then ignoring it until the
grace period following the one in which that CPU sets itself online.
This situation might prove to be fatally disappointing to any RCU
read-side critical sections that had the misfortune to execute during
the time in which RCU was ignoring the slow-to-come-online CPU.This commit therefore updates RCU's internal CPU state-tracking
information at notify_cpu_starting() time, thus providing RCU with
an exact transition of the CPU's state from offline to online.Note that this means that incoming CPUs must not use RCU read-side
critical section (other than those of SRCU) until notify_cpu_starting()
time. Note also that the CPU_STARTING notifiers -are- allowed to use
RCU read-side critical sections. (Of course, CPU-hotplug notifiers are
rapidly becoming obsolete, so you need to act fast!)If a given architecture or CPU family needs to use RCU read-side
critical sections earlier, the call to rcu_cpu_starting() from
notify_cpu_starting() will need to be architecture-specific, with
architectures that need early use being required to hand-place
the call to rcu_cpu_starting() at some point preceding the call to
notify_cpu_starting().Signed-off-by: Paul E. McKenney
-
Currently, __note_gp_changes() checks to see if the CPU has slept through
multiple grace periods. If it has, it resynchronizes that CPU's view
of the grace-period state, which includes whether or not the current
grace period needs a quiescent state from this CPU. The fact of this
need (or lack thereof) needs to be in two places, rdp->cpu_no_qs.b.norm
and rdp->core_needs_qs. The former tells RCU's context-switch code to
go get a quiescent state and the latter says that it needs to be reported.
The current code unconditionally sets the former to true, but correctly
sets the latter.This does not result in failures, but it does unnecessarily increase
the amount of work done on average at context-switch time. This commit
therefore correctly sets both fields.Signed-off-by: Paul E. McKenney
-
The Kconfig currently controlling compilation of tree.c is:
init/Kconfig:config TREE_RCU
init/Kconfig: bool...and update.c and sync.c are "obj-y" meaning that none are ever
built as a module by anyone.Since MODULE_ALIAS is a no-op for non-modular code, we can remove
them from these files.We leave moduleparam.h behind since the files instantiate some boot
time configuration parameters with module_param() still.Cc: "Paul E. McKenney"
Cc: Josh Triplett
Cc: Steven Rostedt
Cc: Mathieu Desnoyers
Cc: Lai Jiangshan
Signed-off-by: Paul Gortmaker
Signed-off-by: Paul E. McKenney -
Commit abedf8e2419f ("rcu: Use simple wait queues where possible in
rcutree") converts Tree RCU's wait queues to simple wait queues,
but it incorrectly reverts the commit 2aa792e6faf1 ("rcu: Use
rcu_gp_kthread_wake() to wake up grace period kthreads"). This can
result in redundant self-wakeups.This commit therefore replaces the simple wait-queue wakeups with
rcu_gp_kthread_wake(), thus avoiding the redundant wakeups.Signed-off-by: Jisheng Zhang
Signed-off-by: Paul E. McKenney -
This commit improves the accuracy of the interaction between CPU hotplug
operations and RCU's expedited grace periods by using RCU's online-CPU
state to determine when failed IPIs should be retried.Signed-off-by: Paul E. McKenney
-
The expedited RCU grace periods currently rely on a failure indication
from smp_call_function_single() to determine that a given CPU is offline.
This works after a fashion, but is more contorted and less precise than
relying on RCU's internal state. This commit therefore takes a first
step towards relying on internal state.Signed-off-by: Paul E. McKenney
-
The expedited RCU CPU stall warnings currently responds to neither the
panic_on_rcu_stall sysctl setting nor the rcupdate.rcu_cpu_stall_suppress
kernel boot parameter. This commit therefore updates the expedited code
to respond to these two controls.Signed-off-by: Paul E. McKenney
-
Now that RCU expedited grace periods are always driven by a workqueue,
there is no need to account for signal reception, and thus no need
to disable expedited RCU CPU stall warnings due to signal reception.
This commit therefore removes the signal-reception checks, leaving a
WARN_ON() to catch possible future bugs.Signed-off-by: Paul E. McKenney
-
The current implementation of expedited grace periods has the user
task drive the grace period. This works, but has downsides: (1) The
user task must awaken tasks piggybacking on this grace period, which
can result in latencies rivaling that of the grace period itself, and
(2) User tasks can receive signals, which interfere with RCU CPU stall
warnings.This commit therefore uses workqueues to drive the grace periods, so
that the user task need not do the awakening. A subsequent commit
will remove the now-unnecessary code allowing for signals.Signed-off-by: Paul E. McKenney
-
The functions synchronize_rcu_expedited() and synchronize_sched_expedited()
have nearly identical code. This commit therefore consolidates this code
into a new _synchronize_rcu_expedited() function.Signed-off-by: Paul E. McKenney
22 Aug, 2016
1 commit
-
Carrying out the following steps results in a softlockup in the
RCU callback-offload (rcuo) kthreads:1. Connect to ixgbevf, and set the speed to 10Gb/s.
2. Use ifconfig to bring the nic up and down repeatedly.[ 317.005148] IPv6: ADDRCONF(NETDEV_CHANGE): eth2: link becomes ready
[ 368.106005] BUG: soft lockup - CPU#1 stuck for 22s! [rcuos/1:15]
[ 368.106005] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[ 368.106005] task: ffff88057dd8a220 ti: ffff88057dd9c000 task.ti: ffff88057dd9c000
[ 368.106005] RIP: 0010:[] [] fib_table_lookup+0x14/0x390
[ 368.106005] RSP: 0018:ffff88061fc83ce8 EFLAGS: 00000286
[ 368.106005] RAX: 0000000000000001 RBX: 00000000020155c0 RCX: 0000000000000001
[ 368.106005] RDX: ffff88061fc83d50 RSI: ffff88061fc83d70 RDI: ffff880036d11a00
[ 368.106005] RBP: ffff88061fc83d08 R08: 0000000000000001 R09: 0000000000000000
[ 368.106005] R10: ffff880036d11a00 R11: ffffffff819e0900 R12: ffff88061fc83c58
[ 368.106005] R13: ffffffff816154dd R14: ffff88061fc83d08 R15: 00000000020155c0
[ 368.106005] FS: 0000000000000000(0000) GS:ffff88061fc80000(0000) knlGS:0000000000000000
[ 368.106005] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 368.106005] CR2: 00007f8c2aee9c40 CR3: 000000057b222000 CR4: 00000000000407e0
[ 368.106005] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 368.106005] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
[ 368.106005] Stack:
[ 368.106005] 00000000010000c0 ffff88057b766000 ffff8802e380b000 ffff88057af03e00
[ 368.106005] ffff88061fc83dc0 ffffffff815349a6 ffff88061fc83d40 ffffffff814ee146
[ 368.106005] ffff8802e380af00 00000000e380af00 ffffffff819e0900 020155c0010000c0
[ 368.106005] Call Trace:
[ 368.106005]
[ 368.106005]
[ 368.106005] [] ip_route_input_noref+0x516/0xbd0
[ 368.106005] [] ? skb_release_data+0xd6/0x110
[ 368.106005] [] ? kfree_skb+0x3a/0xa0
[ 368.106005] [] ip_rcv_finish+0x29f/0x350
[ 368.106005] [] ip_rcv+0x234/0x380
[ 368.106005] [] __netif_receive_skb_core+0x676/0x870
[ 368.106005] [] __netif_receive_skb+0x18/0x60
[ 368.106005] [] process_backlog+0xae/0x180
[ 368.106005] [] net_rx_action+0x152/0x240
[ 368.106005] [] __do_softirq+0xef/0x280
[ 368.106005] [] call_softirq+0x1c/0x30
[ 368.106005]
[ 368.106005]
[ 368.106005] [] do_softirq+0x65/0xa0
[ 368.106005] [] local_bh_enable+0x94/0xa0
[ 368.106005] [] rcu_nocb_kthread+0x232/0x370
[ 368.106005] [] ? wake_up_bit+0x30/0x30
[ 368.106005] [] ? rcu_start_gp+0x40/0x40
[ 368.106005] [] kthread+0xcf/0xe0
[ 368.106005] [] ? kthread_create_on_node+0x140/0x140
[ 368.106005] [] ret_from_fork+0x58/0x90
[ 368.106005] [] ? kthread_create_on_node+0x140/0x140==================================cut here==============================
It turns out that the rcuos callback-offload kthread is busy processing
a very large quantity of RCU callbacks, and it is not reliquishing the
CPU while doing so. This commit therefore adds an cond_resched_rcu_qs()
within the loop to allow other tasks to run.Signed-off-by: Ding Tianhong
[ paulmck: Substituted cond_resched_rcu_qs for cond_resched. ]
Signed-off-by: Paul E. McKenney
18 Aug, 2016
1 commit
-
The current percpu-rwsem read side is entirely free of serializing insns
at the cost of having a synchronize_sched() in the write path.The latency of the synchronize_sched() is too high for cgroups. The
commit 1ed1328792ff talks about the write path being a fairly cold path
but this is not the case for Android which moves task to the foreground
cgroup and back around binder IPC calls from foreground processes to
background processes, so it is significantly hotter than human initiated
operations.Switch cgroup_threadgroup_rwsem into the slow mode for now to avoid the
problem, hopefully it should not be that slow after another commit:80127a39681b ("locking/percpu-rwsem: Optimize readers and reduce global impact").
We could just add rcu_sync_enter() into cgroup_init() but we do not want
another synchronize_sched() at boot time, so this patch adds the new helper
which doesn't block but currently can only be called before the first use.Reported-by: John Stultz
Reported-by: Dmitry Shmidt
Signed-off-by: Peter Zijlstra (Intel)
Signed-off-by: Oleg Nesterov
Signed-off-by: Peter Zijlstra (Intel)
Cc: Andrew Morton
Cc: Colin Cross
Cc: Linus Torvalds
Cc: Paul E. McKenney
Cc: Peter Zijlstra
Cc: Rom Lemarchand
Cc: Tejun Heo
Cc: Thomas Gleixner
Cc: Todd Kjos
Link: http://lkml.kernel.org/r/20160811165413.GA22807@redhat.com
Signed-off-by: Ingo Molnar
10 Aug, 2016
1 commit
-
Currently the percpu-rwsem switches to (global) atomic ops while a
writer is waiting; which could be quite a while and slows down
releasing the readers.This patch cures this problem by ordering the reader-state vs
reader-count (see the comments in __percpu_down_read() and
percpu_down_write()). This changes a global atomic op into a full
memory barrier, which doesn't have the global cacheline contention.This also enables using the percpu-rwsem with rcu_sync disabled in order
to bias the implementation differently, reducing the writer latency by
adding some cost to readers.Signed-off-by: Peter Zijlstra (Intel)
Reviewed-by: Oleg Nesterov
Cc: Andrew Morton
Cc: Linus Torvalds
Cc: Paul E. McKenney
Cc: Paul McKenney
Cc: Peter Zijlstra
Cc: Thomas Gleixner
Cc: linux-kernel@vger.kernel.org
[ Fixed modular build. ]
Signed-off-by: Ingo Molnar
30 Jul, 2016
1 commit
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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
...
26 Jul, 2016
1 commit
-
Pull locking updates from Ingo Molnar:
"The locking tree was busier in this cycle than the usual pattern - a
couple of major projects happened to coincide.The main changes are:
- implement the atomic_fetch_{add,sub,and,or,xor}() API natively
across all SMP architectures (Peter Zijlstra)- add atomic_fetch_{inc/dec}() as well, using the generic primitives
(Davidlohr Bueso)- optimize various aspects of rwsems (Jason Low, Davidlohr Bueso,
Waiman Long)- optimize smp_cond_load_acquire() on arm64 and implement LSE based
atomic{,64}_fetch_{add,sub,and,andnot,or,xor}{,_relaxed,_acquire,_release}()
on arm64 (Will Deacon)- introduce smp_acquire__after_ctrl_dep() and fix various barrier
mis-uses and bugs (Peter Zijlstra)- after discovering ancient spin_unlock_wait() barrier bugs in its
implementation and usage, strengthen its semantics and update/fix
usage sites (Peter Zijlstra)- optimize mutex_trylock() fastpath (Peter Zijlstra)
- ... misc fixes and cleanups"
* 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (67 commits)
locking/atomic: Introduce inc/dec variants for the atomic_fetch_$op() API
locking/barriers, arch/arm64: Implement LDXR+WFE based smp_cond_load_acquire()
locking/static_keys: Fix non static symbol Sparse warning
locking/qspinlock: Use __this_cpu_dec() instead of full-blown this_cpu_dec()
locking/atomic, arch/tile: Fix tilepro build
locking/atomic, arch/m68k: Remove comment
locking/atomic, arch/arc: Fix build
locking/Documentation: Clarify limited control-dependency scope
locking/atomic, arch/rwsem: Employ atomic_long_fetch_add()
locking/atomic, arch/qrwlock: Employ atomic_fetch_add_acquire()
locking/atomic, arch/mips: Convert to _relaxed atomics
locking/atomic, arch/alpha: Convert to _relaxed atomics
locking/atomic: Remove the deprecated atomic_{set,clear}_mask() functions
locking/atomic: Remove linux/atomic.h:atomic_fetch_or()
locking/atomic: Implement atomic{,64,_long}_fetch_{add,sub,and,andnot,or,xor}{,_relaxed,_acquire,_release}()
locking/atomic: Fix atomic64_relaxed() bits
locking/atomic, arch/xtensa: Implement atomic_fetch_{add,sub,and,or,xor}()
locking/atomic, arch/x86: Implement atomic{,64}_fetch_{add,sub,and,or,xor}()
locking/atomic, arch/tile: Implement atomic{,64}_fetch_{add,sub,and,or,xor}()
locking/atomic, arch/sparc: Implement atomic{,64}_fetch_{add,sub,and,or,xor}()
...
15 Jul, 2016
1 commit
-
Straight forward conversion to the state machine. Though the question arises
whether this needs really all these state transitions to work.Signed-off-by: Thomas Gleixner
Signed-off-by: Anna-Maria Gleixner
Reviewed-by: Sebastian Andrzej Siewior
Cc: Linus Torvalds
Cc: Paul E. McKenney
Cc: Peter Zijlstra
Cc: rt@linutronix.de
Link: http://lkml.kernel.org/r/20160713153337.982013161@linutronix.de
Signed-off-by: Ingo Molnar
16 Jun, 2016
5 commits
-
doc.2016.06.15a: Documentation updates
fixes.2016.06.15b: Documentation updates
torture.2016.06.14a: Documentation updates -
In many cases in the RCU tree code, we iterate over the set of cpus for
a leaf node described by rcu_node::grplo and rcu_node::grphi, checking
per-cpu data for each cpu in this range. However, if the set of possible
cpus is sparse, some cpus described in this range are not possible, and
thus no per-cpu region will have been allocated (or initialised) for
them by the generic percpu code.Erroneous accesses to a per-cpu area for these !possible cpus may fault
or may hit other data depending on the addressed generated when the
erroneous per cpu offset is applied. In practice, both cases have been
observed on arm64 hardware (the former being silent, but detectable with
additional patches).To avoid issues resulting from this, we must iterate over the set of
*possible* cpus for a given leaf node. This patch add a new helper,
for_each_leaf_node_possible_cpu, to enable this. As iteration is often
intertwined with rcu_node local bitmask manipulation, a new
leaf_node_cpu_bit helper is added to make this simpler and more
consistent. The RCU tree code is made to use both of these where
appropriate.Without this patch, running reboot at a shell can result in an oops
like:[ 3369.075979] Unable to handle kernel paging request at virtual address ffffff8008b21b4c
[ 3369.083881] pgd = ffffffc3ecdda000
[ 3369.087270] [ffffff8008b21b4c] *pgd=00000083eca48003, *pud=00000083eca48003, *pmd=0000000000000000
[ 3369.096222] Internal error: Oops: 96000007 [#1] PREEMPT SMP
[ 3369.101781] Modules linked in:
[ 3369.104825] CPU: 2 PID: 1817 Comm: NetworkManager Tainted: G W 4.6.0+ #3
[ 3369.121239] task: ffffffc0fa13e000 ti: ffffffc3eb940000 task.ti: ffffffc3eb940000
[ 3369.128708] PC is at sync_rcu_exp_select_cpus+0x188/0x510
[ 3369.134094] LR is at sync_rcu_exp_select_cpus+0x104/0x510
[ 3369.139479] pc : [] lr : [] pstate: 200001c5
[ 3369.146860] sp : ffffffc3eb9435a0
[ 3369.150162] x29: ffffffc3eb9435a0 x28: ffffff8008be4f88
[ 3369.155465] x27: ffffff8008b66c80 x26: ffffffc3eceb2600
[ 3369.160767] x25: 0000000000000001 x24: ffffff8008be4f88
[ 3369.166070] x23: ffffff8008b51c3c x22: ffffff8008b66c80
[ 3369.171371] x21: 0000000000000001 x20: ffffff8008b21b40
[ 3369.176673] x19: ffffff8008b66c80 x18: 0000000000000000
[ 3369.181975] x17: 0000007fa951a010 x16: ffffff80086a30f0
[ 3369.187278] x15: 0000007fa9505590 x14: 0000000000000000
[ 3369.192580] x13: ffffff8008b51000 x12: ffffffc3eb940000
[ 3369.197882] x11: 0000000000000006 x10: ffffff8008b51b78
[ 3369.203184] x9 : 0000000000000001 x8 : ffffff8008be4000
[ 3369.208486] x7 : ffffff8008b21b40 x6 : 0000000000001003
[ 3369.213788] x5 : 0000000000000000 x4 : ffffff8008b27280
[ 3369.219090] x3 : ffffff8008b21b4c x2 : 0000000000000001
[ 3369.224406] x1 : 0000000000000001 x0 : 0000000000000140
...
[ 3369.972257] [] sync_rcu_exp_select_cpus+0x188/0x510
[ 3369.978685] [] synchronize_rcu_expedited+0x64/0xa8
[ 3369.985026] [] synchronize_net+0x24/0x30
[ 3369.990499] [] dev_deactivate_many+0x28c/0x298
[ 3369.996493] [] __dev_close_many+0x60/0xd0
[ 3370.002052] [] __dev_close+0x28/0x40
[ 3370.007178] [] __dev_change_flags+0x8c/0x158
[ 3370.012999] [] dev_change_flags+0x20/0x60
[ 3370.018558] [] do_setlink+0x288/0x918
[ 3370.023771] [] rtnl_newlink+0x398/0x6a8
[ 3370.029158] [] rtnetlink_rcv_msg+0xe4/0x220
[ 3370.034891] [] netlink_rcv_skb+0xc4/0xf8
[ 3370.040364] [] rtnetlink_rcv+0x2c/0x40
[ 3370.045663] [] netlink_unicast+0x160/0x238
[ 3370.051309] [] netlink_sendmsg+0x2f0/0x358
[ 3370.056956] [] sock_sendmsg+0x18/0x30
[ 3370.062168] [] ___sys_sendmsg+0x26c/0x280
[ 3370.067728] [] __sys_sendmsg+0x44/0x88
[ 3370.073027] [] SyS_sendmsg+0x10/0x20
[ 3370.078153] [] el0_svc_naked+0x24/0x28Signed-off-by: Mark Rutland
Reported-by: Dennis Chen
Cc: Catalin Marinas
Cc: Josh Triplett
Cc: Lai Jiangshan
Cc: Mathieu Desnoyers
Cc: Steve Capper
Cc: Steven Rostedt
Cc: Will Deacon
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Paul E. McKenney -
It is not always easy to determine the cause of an RCU stall just by
analysing the RCU stall messages, mainly when the problem is caused
by the indirect starvation of rcu threads. For example, when preempt_rcu
is not awakened due to the starvation of a timer softirq.We have been hard coding panic() in the RCU stall functions for
some time while testing the kernel-rt. But this is not possible in
some scenarios, like when supporting customers.This patch implements the sysctl kernel.panic_on_rcu_stall. If
set to 1, the system will panic() when an RCU stall takes place,
enabling the capture of a vmcore. The vmcore provides a way to analyze
all kernel/tasks states, helping out to point to the culprit and the
solution for the stall.The kernel.panic_on_rcu_stall sysctl is disabled by default.
Changes from v1:
- Fixed a typo in the git log
- The if(sysctl_panic_on_rcu_stall) panic() is in a static function
- Fixed the CONFIG_TINY_RCU compilation issue
- The var sysctl_panic_on_rcu_stall is now __read_mostlyCc: Jonathan Corbet
Cc: "Paul E. McKenney"
Cc: Josh Triplett
Cc: Steven Rostedt
Cc: Mathieu Desnoyers
Cc: Lai Jiangshan
Acked-by: Christian Borntraeger
Reviewed-by: Josh Triplett
Reviewed-by: Arnaldo Carvalho de Melo
Tested-by: "Luis Claudio R. Goncalves"
Signed-off-by: Daniel Bristot de Oliveira
Signed-off-by: Paul E. McKenney -
In the area in hot pursuit of a bug, so might as well clean it up.
Signed-off-by: Paul E. McKenney
-
Currently, if the very first call to call_rcu_tasks() has irqs disabled,
it will create the rcu_tasks_kthread with irqs disabled, which will
result in a splat in the memory allocator, which kthread_run() invokes
with the expectation that irqs are enabled.This commit fixes this problem by deferring kthread creation if called
with irqs disabled. The first call to call_rcu_tasks() that has irqs
enabled will create the kthread.This bug was detected by rcutorture changes that were motivated by
Iftekhar Ahmed's mutation-testing efforts.Signed-off-by: Paul E. McKenney
15 Jun, 2016
9 commits
-
Fix to return a negative error code -ENOMEM from kcalloc() error
handling case instead of 0, as done elsewhere in this function.Signed-off-by: Wei Yongjun
Signed-off-by: Paul E. McKenney -
0day found a boot warning triggered in rcu_perf_writer() on !SMP kernel:
WARN_ON(rcu_gp_is_normal() && gp_exp);
, the root cause of which is trying to measure expedited grace
periods(by setting gp_exp to true by default) when all the grace periods
are normal(TINY RCU only has normal grace periods).However, such a mis-setting would only result in failing to measure the
performance for a specific kind of grace periods, therefore using a
WARN_ON to check this is a little overkilling. We could handle this
inside rcuperf module via some error messages to tell users about the
mis-settings.Therefore this patch removes the WARN_ON in rcu_perf_writer() and
handles those checkings in rcu_perf_init() with plain if() code.Moreover, this patch changes the default value of gp_exp to 1) align
with rcutorture tests and 2) make the default setting work for all RCU
implementations by default.Suggested-by: Paul E. McKenney
Signed-off-by: Boqun Feng
Fixes: http://lkml.kernel.org/r/57411b10.mFvG0+AgcrMXGtcj%fengguang.wu@intel.com
Signed-off-by: Paul E. McKenney -
This commit removes CONFIG_RCU_TORTURE_TEST_RUNNABLE in favor of the
already-existing rcutorture.torture_runnable kernel boot parameter.
It also converts an #ifdef into IS_ENABLED(), saving a few lines of code.Signed-off-by: Paul E. McKenney
-
This commit applies the infamous IS_ENABLED() macro to eliminate a #ifdef.
It also eliminates the RCU_PERF_TEST_RUNNABLE Kconfig option in favor
of the already-existing rcuperf.perf_runnable kernel boot parameter.Signed-off-by: Paul E. McKenney
-
People have been having some difficulty finding their way around the
RCU code. This commit therefore pulls some of the expedited grace-period
code from tree_plugin.h to a new tree_exp.h file. This commit is strictly
code movement.Signed-off-by: Paul E. McKenney
-
People have been having some difficulty finding their way around the
RCU code. This commit therefore pulls some of the expedited grace-period
code from tree.c to a new tree_exp.h file. This commit is strictly code
movement, with the exception of a forward declaration that was added
for the sync_sched_exp_online_cleanup() function.A subsequent commit will move the remaining expedited grace-period code
from tree_plugin.h to tree_exp.h.Signed-off-by: Paul E. McKenney
-
I think you'll find this condition is superfluous, as the whole function
is under #ifdef of that same.Signed-off-by: Peter Zijlstra (Intel)
Signed-off-by: Paul E. McKenney -
In the past, RCU grace-period initialization excluded CPU-hotplug
operations, but this is no longer the case. This commit therefore
removed an outdated comment in rcu_gp_init() claiming that these
are excluded.Reported-by: Lihao Liang
Signed-off-by: Paul E. McKenney -
The comment header for rcu_scheduler_active states that it is used
to optimize synchronize_sched() at early boot. This is incorrect.
The synchronize_sched() function instead checks the number of online
CPUs. This commit therefore replaces the comment's synchronize_sched()
with synchronize_rcu(), which really does use rcu_scheduler_active for
this purpose.Reported-by: Lihao Liang
Signed-off-by: Paul E. McKenney
