22 Feb, 2012
35 commits
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synchronize_sched_expedited() is spamming CONFIG_DEBUG_PREEMPT=y
users with an unintended warning from the cpu_is_offline() check: use
raw_smp_processor_id() instead of smp_processor_id() there.Because the warning is under a get_online_cpus(), it is not possible
for any CPUs to go offline, though it is quite possible that the
task might migrate between the raw_smp_processor_id() and the check
of cpu_is_offline(). This is not a problem because the task cannot
migrate from an offline CPU to an online one or vice versa. The point
of the check is to verify that synchronize_sched_expedited() is not
called from an offline CPU, for example, from a CPU_DYING notifier, or,
more important, from an outgoing CPU making its way from its CPU_DYING
notifiers to the idle loop.Signed-off-by: Hugh Dickins
Signed-off-by: Paul E. McKenney -
This commit handles workloads that transition quickly between idle and
non-idle, and where the CPU's callbacks cannot be invoked, but where
RCU does not have anything immediate for the CPU to do. Without this
patch, the RCU_FAST_NO_HZ code can be invoked repeatedly on each entry
to idle. The commit sets the per-CPU rcu_dyntick_holdoff variable to
hold off further attempts for a tick.Reported-by: "Abou Gazala, Neven M"
Signed-off-by: Paul E. McKenney
Signed-off-by: Paul E. McKenney -
If a softirq is pending, the current CPU has RCU callbacks pending,
and RCU does not immediately need anything from this CPU, then the
current code resets the RCU_FAST_NO_HZ state machine. This means that
upon exit from the subsequent softirq handler, RCU_FAST_NO_HZ will
try really hard to force RCU into dyntick-idle mode. And if the same
conditions hold after a few tries (determined by RCU_IDLE_OPT_FLUSHES),
the same situation can repeat, possibly endlessly. This scenario is
not particularly good for battery lifetime.This commit therefore suppresses the early exit from the RCU_FAST_NO_HZ
state machine in the case where there is a softirq pending. This change
forces the state machine to retain its memory, and to enter holdoff if
this condition persists.Reported-by: "Abou Gazala, Neven M"
Signed-off-by: Paul E. McKenney
Signed-off-by: Paul E. McKenney -
RCU, RCU-bh, and RCU-sched read-side critical sections are forbidden
in the inner idle loop, that is, between the rcu_idle_enter() and the
rcu_idle_exit() -- RCU will happily ignore any such read-side critical
sections. However, things like powertop need tracepoints in the inner
idle loop.This commit therefore provides an RCU_NONIDLE() macro that can be used to
wrap code in the idle loop that requires RCU read-side critical sections.Suggested-by: Steven Rostedt
Signed-off-by: Paul E. McKenney
Signed-off-by: Paul E. McKenney
Reviewed-by: Josh Triplett
Acked-by: Deepthi Dharwar -
Use of RCU in the idle loop is incorrect, quite a few instances of
just that have made their way into mainline, primarily event tracing.
The problem with RCU read-side critical sections on CPUs that RCU believes
to be idle is that RCU is completely ignoring the CPU, along with any
attempts and RCU read-side critical sections.The approaches of eliminating the offending uses and of pushing the
definition of idle down beyond the offending uses have both proved
impractical. The new approach is to encapsulate offending uses of RCU
with rcu_idle_exit() and rcu_idle_enter(), but this requires nesting
for code that is invoked both during idle and and during normal execution.
Therefore, this commit modifies rcu_idle_enter() and rcu_idle_exit() to
permit nesting.Signed-off-by: Paul E. McKenney
Signed-off-by: Paul E. McKenney
Reviewed-by: Josh Triplett
Acked-by: Deepthi Dharwar -
There is now an unconditional check for rcu_head misalignment in
__call_rcu(), so remove the old conditional one in debug_rcu_head_queue().Reported-by: Josh Triplett
Signed-off-by: Paul E. McKenney -
The semantic match that finds this problem is as follows:
(http://coccinelle.lip6.fr/)//
@@
expression e,e1;
constant c;
@@*e = c
... when != e = e1
when != &e
when != true IS_ERR(e)
*PTR_ERR(e)
//Signed-off-by: Julia Lawall
Reported-by: Josh Triplett
Signed-off-by: Paul E. McKenney -
Fix a bonehead error introduced when adding event tracing to rcutorture.
Move the traces to follow the NULL-pointer checks.Signed-off-by: Paul E. McKenney
-
The expedited RCU primitives can be quite useful, but they have some
high costs as well. This commit updates and creates docbook comments
calling out the costs, and updates the RCU documentation as well.Signed-off-by: Paul E. McKenney
-
Because newly offlined CPUs continue executing after completing the
CPU_DYING notifiers, they legitimately enter the scheduler and use
RCU while appearing to be offline. This calls for a more sophisticated
approach as follows:1. RCU marks the CPU online during the CPU_UP_PREPARE phase.
2. RCU marks the CPU offline during the CPU_DEAD phase.
3. Diagnostics regarding use of read-side RCU by offline CPUs use
RCU's accounting rather than the cpu_online_map. (Note that
__call_rcu() still uses cpu_online_map to detect illegal
invocations within CPU_DYING notifiers.)4. Offline CPUs are prevented from hanging the system by
force_quiescent_state(), which pays attention to cpu_online_map.
Some additional work (in a later commit) will be needed to
guarantee that force_quiescent_state() waits a full jiffy before
assuming that a CPU is offline, for example, when called from
idle entry. (This commit also makes the one-jiffy wait
explicit, since the old-style implicit wait can now be defeated
by RCU_FAST_NO_HZ and by rcutorture.)This approach avoids the false positives encountered when attempting to
use more exact classification of CPU online/offline state.Signed-off-by: Paul E. McKenney
Signed-off-by: Paul E. McKenney -
It is illegal to use RCU from a CPU that has reported idleness or
offlinedness to RCU. However, it can be quite difficult to determine
from a stack trace whether or not a given CPU is idle or offline.
Therefore, this commit adds idle/offline diagnostics to the lockdep-RCU
error message.Signed-off-by: Paul E. McKenney
Signed-off-by: Paul E. McKenney -
The rcu_prepare_for_idle() function is always called with interrupts
disabled, so there is no reason to disable interrupts again within
rcu_prepare_for_idle(). Therefore, this commit removes all of the
interrupt disabling, also removing a latent disabling-unbalance bug.Signed-off-by: Paul E. McKenney
Signed-off-by: Paul E. McKenney -
Now that TREE_RCU and TREE_PREEMPT_RCU no longer do anything different
for the single-CPU case, there is no need for multiple definitions of
synchronize_sched_expedited(). It is no longer in any sense a plug-in,
so move it from kernel/rcutree_plugin.h to kernel/rcutree.c.Signed-off-by: Paul E. McKenney
Signed-off-by: Paul E. McKenney -
Although it is legal to use RCU during early boot, it is anything
but legal to use RCU at runtime from an offlined CPU. After all, RCU
explicitly ignores offlined CPUs. This commit therefore adds checks
for runtime use of RCU from offlined CPUs.These checks are not perfect, in particular, they can be subverted
through use of things like rcu_dereference_raw(). Note that it is not
possible to put checks in rcu_read_lock() and friends due to the fact
that these primitives are used in code that might be used under either
RCU or lock-based protection, which means that checking rcu_read_lock()
gets you fat piles of false positives.Signed-off-by: Paul E. McKenney
Signed-off-by: Paul E. McKenney -
Add module parameters to rcutorture that induce a CPU stall.
The stall_cpu parameter specifies how long to stall in seconds,
defaulting to zero, which indicates no stalling is to be undertaken.
The stall_cpu_holdoff parameter specifies how many seconds after
insmod (or boot, if rcutorture is built into the kernel) that this
stall is to start. The default value for stall_cpu_holdoff is ten
seconds.Signed-off-by: Paul E. McKenney
Signed-off-by: Paul E. McKenney -
When rcutorture is started automatically at boot time, it might well
also start CPU-hotplug operations at that time, which might not be
desirable. This commit therefore adds an rcutorture parameter that
allows CPU-hotplug operations to be held off for the specified number
of seconds after the start of boot.Signed-off-by: Paul E. McKenney
Signed-off-by: Paul E. McKenney -
There have been situations where RCU CPU stall warnings were caused by
issues in scheduling-clock timer initialization. To make it easier to
track these down, this commit causes the RCU CPU stall-warning messages
to print out the number of scheduling-clock interrupts taken in the
current grace period for each stalled CPU.Signed-off-by: Paul E. McKenney
Signed-off-by: Paul E. McKenney -
The default CONFIG_RCU_CPU_STALL_TIMEOUT value of 60 seconds has served
Linux users well for production use for quite some time. However, for
debugging, there will be more than three minutes between subsequent
stall-warning messages. This can be an annoyingly long wait if you
are trying to work out where the offending infinite loop is hiding.Therefore, this commit provides a rcu_cpu_stall_timeout sysfs
parameter that may be adjusted at boot time and at runtime to speed
up debugging.Signed-off-by: Paul E. McKenney
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Now that both TINY_RCU and TINY_PREEMPT_RCU have been in place for awhile,
it is time to remove UP support from TREE_RCU, which is what this commit
does.Signed-off-by: Paul E. McKenney
Signed-off-by: Paul E. McKenney -
The inner idle loop is an extended quiescent state for all flavors
of RCU, but there have been recent bug involving use of RCU read-side
primitives from within the idle loop. Therefore, this commit enlists
lockdep-RCU to detect attempts to enter the inner idle loop while in
an RCU read-side critical section, emitting a lockdep-RCU splat if so.Signed-off-by: Paul E. McKenney
Signed-off-by: Paul E. McKenney -
The recent updates to RCU_CPU_FAST_NO_HZ have an rcu_needs_cpu() that
does more than just check for callbacks, so get the name for
rcu_preempt_needs_cpu() consistent with that change, now calling it
rcu_preempt_cpu_has_callbacks().Signed-off-by: Paul E. McKenney
Signed-off-by: Paul E. McKenney -
This is a port of commit #82e78d80 from TREE_PREEMPT_RCU to
TINY_PREEMPT_RCU.This commit uses the fact that current->rcu_boost_mutex is set
any time that the RCU_READ_UNLOCK_BOOSTED flag is set in the
current->rcu_read_unlock_special bitmask. This allows tests of
the bit to be changed to tests of the pointer, which in turn allows
the RCU_READ_UNLOCK_BOOSTED flag to be eliminated.Please note that the check of current->rcu_read_unlock_special need not
change because any time that RCU_READ_UNLOCK_BOOSTED was set, so was
RCU_READ_UNLOCK_BLOCKED. Therefore, __rcu_read_unlock() can continue
testing current->rcu_read_unlock_special for non-zero, as before.Signed-off-by: Paul E. McKenney
Signed-off-by: Paul E. McKenney -
This is a port to TINY_RCU of Peter Zijlstra's commit #ec433f0c5
The rcu_read_unlock_special() function relies on in_irq() to exclude
scheduler activity from interrupt level. This fails because exit_irq()
can invoke the scheduler after clearing the preempt_count() bits that
in_irq() uses to determine that it is at interrupt level. This situation
can result in failures as follows:$task IRQ SoftIRQ
rcu_read_lock()
/* do stuff */
|= UNLOCK_BLOCKED
rcu_read_unlock()
--t->rcu_read_lock_nestingirq_enter();
/* do stuff, don't use RCU */
irq_exit();
sub_preempt_count(IRQ_EXIT_OFFSET);
invoke_softirq()ttwu();
spin_lock_irq(&pi->lock)
rcu_read_lock();
/* do stuff */
rcu_read_unlock();
rcu_read_unlock_special()
rcu_report_exp_rnp()
ttwu()
spin_lock_irq(&pi->lock) /* deadlock */rcu_read_unlock_special(t);
This can be triggered 'easily' because invoke_softirq() immediately does
a ttwu() of ksoftirqd/# instead of doing the in-place softirq stuff first,
but even without that the above happens.Cure this by also excluding softirqs from the rcu_read_unlock_special()
handler and ensuring the force_irqthreads ksoftirqd/# wakeup is done
from full softirq context.It is also necessary to delay the ->rcu_read_lock_nesting decrement until
after rcu_read_unlock_special(). This delay is handled by the commit
"Protect __rcu_read_unlock() against scheduler-using irq handlers".Signed-off-by: Peter Zijlstra
Signed-off-by: Paul E. McKenney
Signed-off-by: Paul E. McKenney -
This is a port of commit #b0d3041 from TREE_RCU to TREE_PREEMPT_RCU.
Under some rare but real combinations of configuration parameters, RCU
callbacks are posted during early boot that use kernel facilities that are
not yet initialized. Therefore, when these callbacks are invoked, hard
hangs and crashes ensue. This commit therefore prevents RCU callbacks
from being invoked until after the scheduler is fully up and running,
as in after multiple tasks have been spawned.It might well turn out that a better approach is to identify the specific
RCU callbacks that are causing this problem, but that discussion will
wait until such time as someone really needs an RCU callback to be invoked
(as opposed to merely registered) during early boot.Signed-off-by: Paul E. McKenney
Signed-off-by: Paul E. McKenney -
This is a port of commit #be0e1e21 to TINY_PREEMPT_RCU. This uses
noinline to prevent rcu_read_unlock_special() from being inlined into
__rcu_read_unlock().Signed-off-by: Paul E. McKenney
-
This commit ports commit #10f39bb1b2 (rcu: protect __rcu_read_unlock()
against scheduler-using irq handlers) from TREE_PREEMPT_RCU to
TINY_PREEMPT_RCU. The following is a corresponding port of that
commit message.The addition of RCU read-side critical sections within runqueue and
priority-inheritance critical sections introduced some deadlocks,
for example, involving interrupts from __rcu_read_unlock() where the
interrupt handlers call wake_up(). This situation can cause the
instance of __rcu_read_unlock() invoked from interrupt to do some
of the processing that would otherwise have been carried out by the
task-level instance of __rcu_read_unlock(). When the interrupt-level
instance of __rcu_read_unlock() is called with a scheduler lock held from
interrupt-entry/exit situations where in_irq() returns false, deadlock can
result. Of course, in a UP kernel, there are not really any deadlocks,
but the upper-level critical section can still be be fatally confused
by the lower-level critical section changing things out from under it.This commit resolves these deadlocks by using negative values of the
per-task ->rcu_read_lock_nesting counter to indicate that an instance of
__rcu_read_unlock() is in flight, which in turn prevents instances from
interrupt handlers from doing any special processing. Note that nested
rcu_read_lock()/rcu_read_unlock() pairs are still permitted, but they will
never see ->rcu_read_lock_nesting go to zero, and will therefore never
invoke rcu_read_unlock_special(), thus preventing them from seeing the
RCU_READ_UNLOCK_BLOCKED bit should it be set in ->rcu_read_unlock_special.
This patch also adds a check for ->rcu_read_unlock_special being negative
in rcu_check_callbacks(), thus preventing the RCU_READ_UNLOCK_NEED_QS
bit from being set should a scheduling-clock interrupt occur while
__rcu_read_unlock() is exiting from an outermost RCU read-side critical
section.Of course, __rcu_read_unlock() can be preempted during the time that
->rcu_read_lock_nesting is negative. This could result in the setting
of the RCU_READ_UNLOCK_BLOCKED bit after __rcu_read_unlock() checks it,
and would also result it this task being queued on the corresponding
rcu_node structure's blkd_tasks list. Therefore, some later RCU read-side
critical section would enter rcu_read_unlock_special() to clean up --
which could result in deadlock (OK, OK, fatal confusion) if that RCU
read-side critical section happened to be in the scheduler where the
runqueue or priority-inheritance locks were held.To prevent the possibility of fatal confusion that might result from
preemption during the time that ->rcu_read_lock_nesting is negative,
this commit also makes rcu_preempt_note_context_switch() check for
negative ->rcu_read_lock_nesting, thus refraining from queuing the task
(and from setting RCU_READ_UNLOCK_BLOCKED) if we are already exiting
from the outermost RCU read-side critical section (in other words,
we really are no longer actually in that RCU read-side critical
section). In addition, rcu_preempt_note_context_switch() invokes
rcu_read_unlock_special() to carry out the cleanup in this case, which
clears out the ->rcu_read_unlock_special bits and dequeues the task
(if necessary), in turn avoiding needless delay of the current RCU grace
period and needless RCU priority boosting.It is still illegal to call rcu_read_unlock() while holding a scheduler
lock if the prior RCU read-side critical section has ever had both
preemption and irqs enabled. However, the common use case is legal,
namely where then entire RCU read-side critical section executes with
irqs disabled, for example, when the scheduler lock is held across the
entire lifetime of the RCU read-side critical section.Signed-off-by: Paul E. McKenney
Signed-off-by: Paul E. McKenney -
The grace-period initialization sequence in rcu_start_gp() has a special
case for systems where the rcu_node tree is a single rcu_node structure.
This made sense some years ago when systems were smaller and up to 64
CPUs could share a single rcu_node structure, but now that large systems
are common and a given leaf rcu_node structure can support only 16 CPUs
(due to lock contention on the rcu_node's ->lock field), this optimization
is almost never taken. And even the small mobile platforms that might
make use of it might rather have the kernel text reduction.Therefore, this commit removes the check for single-rcu_node trees.
Signed-off-by: Paul E. McKenney
Reviewed-by: Josh Triplett -
RCU's current CPU-offline code path dumps all of the outgoing CPU's
callbacks onto the RCU_NEXT_TAIL portion of the surviving CPU's
callback list. This means that all the ready-to-invoke callbacks from
the outgoing CPU must wait for another full RCU grace period. This was
just fine when CPU-hotplug events were rare, but there is increasing
evidence that users are planning to make increasing use of CPU hotplug.Therefore, this commit changes the callback-dumping procedure so that
callbacks that are ready to invoke are moved to the RCU_DONE_TAIL
portion of the surviving CPU's callback list. This avoids running
these callbacks through a second unnecessary grace period.Signed-off-by: Paul E. McKenney
Signed-off-by: Paul E. McKenney -
Because quiescent states are now reported from offline CPUs in
CPU_DYING state, there is some possibility that such a CPU might
note the end of a grace period and attempt to start invoking
callbacks. This would be a very bad thing, and is supposed to
be prevented by the fact that the CPU_DYING CPU gets rid of all
its callbacks before reporting the quiescent state. However,
there is other CPU-offline code in the kernel, and it is quite
possible that someone will invoke RCU core processing from that
code. Therefore, this commit adds a warning for this case.Signed-off-by: Paul E. McKenney
Signed-off-by: Paul E. McKenney -
Currently, a given CPU is permitted to remain in dyntick-idle mode
indefinitely if it has only lazy RCU callbacks queued. This is vulnerable
to corner cases in NUMA systems, so limit the time to six seconds by
default. (Currently controlled by a cpp macro.)Signed-off-by: Paul E. McKenney
Signed-off-by: Paul E. McKenney -
Make rcutorture check for CPU-hotplug failures and complain if there
were any.Signed-off-by: Paul E. McKenney
Signed-off-by: Paul E. McKenney -
Move ->qsmaskinit and blkd_tasks[] manipulation to the CPU_DYING
notifier. This simplifies the code by eliminating a potential
deadlock and by reducing the responsibilities of force_quiescent_state().
Also rename functions to make their connection to the CPU-hotplug
stages explicit.Signed-off-by: Paul E. McKenney
Signed-off-by: Paul E. McKenney -
When CONFIG_RCU_FAST_NO_HZ is enabled, RCU will allow a given CPU to
enter dyntick-idle mode even if it still has RCU callbacks queued.
RCU avoids system hangs in this case by scheduling a timer for several
jiffies in the future. However, if all of the callbacks on that CPU
are from kfree_rcu(), there is no reason to wake the CPU up, as it is
not a problem to defer freeing of memory.This commit therefore tracks the number of callbacks on a given CPU
that are from kfree_rcu(), and avoids scheduling the timer if all of
a given CPU's callbacks are from kfree_rcu().Signed-off-by: Paul E. McKenney
Signed-off-by: Paul E. McKenney -
The push for energy efficiency will require that RCU tag rcu_head
structures to indicate whether or not their invocation is time critical.
This tagging is best carried out in the bottom bits of the ->next
pointers in the rcu_head structures. This tagging requires that the
rcu_head structures be properly aligned, so this commit adds the required
diagnostics.Signed-off-by: Paul E. McKenney
Signed-off-by: Paul E. McKenney -
It is illegal to have a grace period within a same-flavor RCU read-side
critical section, so this commit adds lockdep-RCU checks to splat when
such abuse is encountered. This commit does not detect more elaborate
RCU deadlock situations. These situations might be a job for lockdep
enhancements.Signed-off-by: Paul E. McKenney
14 Feb, 2012
2 commits
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* tag 'for-linus' of git://github.com/rustyrussell/linux:
module: fix broken isapnp handling in file2alias
module: make module param bint handle nul value -
Allow bint param accept nul values, just do same as bool param.
Signed-off-by: Dave Young
Cc: Rusty Russell
Signed-off-by: Rusty Russell
12 Feb, 2012
1 commit
-
Says Jens:
"Time to push off some of the pending items. I really wanted to wait
until we had the regression nailed, but alas it's not quite there yet.
But I'm very confident that it's "just" a missing expire on exit, so
fix from Tejun should be fairly trivial. I'm headed out for a week on
the slopes.- Killing the barrier part of mtip32xx. It doesn't really support
barriers, and it doesn't need them (writes are fully ordered).- A few fixes from Dan Carpenter, preventing overflows of integer
multiplication.- A fixup for loop, fixing a previous commit that didn't quite solve
the partial read problem from Dave Young.- A bio integer overflow fix from Kent Overstreet.
- Improvement/fix of the door "keep locked" part of the cdrom shared
code from Paolo Benzini.- A few cfq fixes from Shaohua Li.
- A fix for bsg sysfs warning when removing a file it did not create
from Stanislaw Gruszka.- Two fixes for floppy from Vivek, preventing a crash.
- A few block core fixes from Tejun. One killing the over-optimized
ioc exit path, cleaning that up nicely. Two others fixing an oops
on elevator switch, due to calling into the scheduler merge check
code without holding the queue lock."* 'for-linus' of git://git.kernel.dk/linux-block:
block: fix lockdep warning on io_context release put_io_context()
relay: prevent integer overflow in relay_open()
loop: zero fill bio instead of return -EIO for partial read
bio: don't overflow in bio_get_nr_vecs()
floppy: Fix a crash during rmmod
floppy: Cleanup disk->queue before caling put_disk() if add_disk() was never called
cdrom: move shared static to cdrom_device_info
bsg: fix sysfs link remove warning
block: don't call elevator callbacks for plug merges
block: separate out blk_rq_merge_ok() and blk_try_merge() from elevator functions
mtip32xx: removed the irrelevant argument of mtip_hw_submit_io() and the unused member of struct driver_data
block: strip out locking optimization in put_io_context()
cdrom: use copy_to_user() without the underscores
block: fix ioc locking warning
block: fix NULL icq_cache reference
block,cfq: change code order
11 Feb, 2012
1 commit
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* 'perf-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
perf: Fix double start/stop in x86_pmu_start()
perf evsel: Fix an issue where perf report fails to show the proper percentage
perf tools: Fix prefix matching for kernel maps
perf tools: Fix perf stack to non executable on x86_64
perf: Remove deprecated WARN_ON_ONCE()
10 Feb, 2012
1 commit
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"subbuf_size" and "n_subbufs" come from the user and they need to be
capped to prevent an integer overflow.Signed-off-by: Dan Carpenter
Cc: stable@kernel.org
Signed-off-by: Jens Axboe
