Hi,
Testing 2.6.39-rc5 is giving me the following stall:
[ 5767.731001] INFO: rcu_sched_state detected stall on CPU 1 (t=60001 jiffies)
[ 5767.732001] INFO: rcu_sched_state detected stalls on CPUs/tasks: { 1} (detected by 0, t=60002 jiffies)
[ 5947.763001] INFO: rcu_sched_state detected stall on CPU 1 (t=240032 jiffies)
[ 5947.764001] INFO: rcu_sched_state detected stalls on CPUs/tasks: { 1} (detected by 0, t=240034 jiffies)
[ 6024.489362] libceph: mon0 172.17.40.34:6789 socket closed
[ 6121.281139] INFO: task mcelog:6513 blocked for more than 120 seconds.
[ 6121.287575] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[ 6121.295397] ffff880177aefce8 0000000000000082 ffffffff810339b6 ffff880226d35a40
[ 6121.302840] ffff88018226c3b0 ffff88018226c3b0 0000000000011e80 ffff880226d35a40
[ 6121.310284] ffff88018226c760 ffff880177aefe80 ffff880177aefd18 ffffffff813af047
[ 6121.317725] Call Trace:
[ 6121.320176] [<ffffffff810339b6>] ? calc_load_account_idle+0xe/0x1d
[ 6121.326437] [<ffffffff813af047>] schedule+0x159/0x193
[ 6121.331569] [<ffffffff813af449>] schedule_timeout+0x36/0xe2
[ 6121.337223] [<ffffffff810ad9eb>] ? trace_hardirqs_on+0x9/0x20
[ 6121.343047] [<ffffffff813aee2b>] do_wait_for_common+0x97/0xe3
[ 6121.348967] [<ffffffff8103e8fa>] ? try_to_wake_up+0x200/0x200
[ 6121.354794] [<ffffffff8107a4bf>] ? __raw_spin_lock_irq+0x17/0x2f
[ 6121.360878] [<ffffffff813af2a9>] wait_for_common+0x36/0x4d
[ 6121.366441] [<ffffffff813af378>] wait_for_completion+0x1d/0x1f
[ 6121.372356] [<ffffffff8109ae6d>] synchronize_sched+0x40/0x49
[ 6121.378096] [<ffffffff810635b8>] ? find_get_pid+0x1b/0x1b
[ 6121.383574] [<ffffffff81015fe5>] mce_read+0x17f/0x25d
[ 6121.388707] [<ffffffff81111af5>] ? rw_verify_area+0xac/0xdb
[ 6121.394358] [<ffffffff811121f1>] vfs_read+0xa9/0xe1
[ 6121.399317] [<ffffffff8111248d>] sys_read+0x4c/0x70
[ 6121.404278] [<ffffffff813b6deb>] system_call_fastpath+0x16/0x1b
[ 6127.795001] INFO: rcu_sched_state detected stall on CPU 1 (t=420064 jiffies)
[ 6127.796001] INFO: rcu_sched_state detected stalls on CPUs/tasks: { 1} (detected by 0, t=420066 jiffies)
[ 6241.410171] INFO: task mcelog:6513 blocked for more than 120 seconds.
Reverting commit a4dd99250dc makes the stalls go away:
rcu: create new rcu_access_index() and use in mce
The MCE subsystem needs to sample an RCU-protected index outside of
any protection for that index. If this was a pointer, we would use
rcu_access_pointer(), but there is no corresponding rcu_access_index().
This commit therefore creates an rcu_access_index() and applies it
to MCE.
Signed-off-by: Paul E. McKenney <[email protected]>
Tested-by: Zdenek Kabelac <[email protected]>
Here's some bits from my config that might be relevant:
# RCU Subsystem
CONFIG_TREE_RCU=y
# CONFIG_PREEMPT_RCU is not set
# CONFIG_RCU_TRACE is not set
CONFIG_RCU_FANOUT=64
# CONFIG_RCU_FANOUT_EXACT is not set
# CONFIG_RCU_FAST_NO_HZ is not set
# CONFIG_TREE_RCU_TRACE is not set
CONFIG_PREEMPT_NOTIFIERS=y
# CONFIG_PREEMPT_NONE is not set
CONFIG_PREEMPT_VOLUNTARY=y
# CONFIG_PREEMPT is not set
CONFIG_X86_MCE=y
CONFIG_X86_MCE_INTEL=y
CONFIG_X86_MCE_AMD=y
CONFIG_X86_MCE_THRESHOLD=y
# CONFIG_X86_MCE_INJECT is not set
CONFIG_EDAC_DECODE_MCE=y
# CONFIG_EDAC_MCE_INJ is not set
CONFIG_EDAC_MCE=y
# CONFIG_SPARSE_RCU_POINTER is not set
# CONFIG_RCU_TORTURE_TEST is not set
CONFIG_RCU_CPU_STALL_DETECTOR=y
CONFIG_RCU_CPU_STALL_TIMEOUT=60
CONFIG_RCU_CPU_STALL_DETECTOR_RUNNABLE=y
Please let me know if there is anything I can do to help sort this out.
-- Jim
On Wed, Apr 27, 2011 at 01:59:01PM -0600, Jim Schutt wrote:
> Hi,
>
> Testing 2.6.39-rc5 is giving me the following stall:
>
> [ 5767.731001] INFO: rcu_sched_state detected stall on CPU 1 (t=60001 jiffies)
> [ 5767.732001] INFO: rcu_sched_state detected stalls on CPUs/tasks: { 1} (detected by 0, t=60002 jiffies)
> [ 5947.763001] INFO: rcu_sched_state detected stall on CPU 1 (t=240032 jiffies)
> [ 5947.764001] INFO: rcu_sched_state detected stalls on CPUs/tasks: { 1} (detected by 0, t=240034 jiffies)
> [ 6024.489362] libceph: mon0 172.17.40.34:6789 socket closed
> [ 6121.281139] INFO: task mcelog:6513 blocked for more than 120 seconds.
> [ 6121.287575] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> [ 6121.295397] ffff880177aefce8 0000000000000082 ffffffff810339b6 ffff880226d35a40
> [ 6121.302840] ffff88018226c3b0 ffff88018226c3b0 0000000000011e80 ffff880226d35a40
> [ 6121.310284] ffff88018226c760 ffff880177aefe80 ffff880177aefd18 ffffffff813af047
> [ 6121.317725] Call Trace:
> [ 6121.320176] [<ffffffff810339b6>] ? calc_load_account_idle+0xe/0x1d
> [ 6121.326437] [<ffffffff813af047>] schedule+0x159/0x193
> [ 6121.331569] [<ffffffff813af449>] schedule_timeout+0x36/0xe2
> [ 6121.337223] [<ffffffff810ad9eb>] ? trace_hardirqs_on+0x9/0x20
> [ 6121.343047] [<ffffffff813aee2b>] do_wait_for_common+0x97/0xe3
> [ 6121.348967] [<ffffffff8103e8fa>] ? try_to_wake_up+0x200/0x200
> [ 6121.354794] [<ffffffff8107a4bf>] ? __raw_spin_lock_irq+0x17/0x2f
> [ 6121.360878] [<ffffffff813af2a9>] wait_for_common+0x36/0x4d
> [ 6121.366441] [<ffffffff813af378>] wait_for_completion+0x1d/0x1f
> [ 6121.372356] [<ffffffff8109ae6d>] synchronize_sched+0x40/0x49
> [ 6121.378096] [<ffffffff810635b8>] ? find_get_pid+0x1b/0x1b
> [ 6121.383574] [<ffffffff81015fe5>] mce_read+0x17f/0x25d
> [ 6121.388707] [<ffffffff81111af5>] ? rw_verify_area+0xac/0xdb
> [ 6121.394358] [<ffffffff811121f1>] vfs_read+0xa9/0xe1
> [ 6121.399317] [<ffffffff8111248d>] sys_read+0x4c/0x70
> [ 6121.404278] [<ffffffff813b6deb>] system_call_fastpath+0x16/0x1b
> [ 6127.795001] INFO: rcu_sched_state detected stall on CPU 1 (t=420064 jiffies)
> [ 6127.796001] INFO: rcu_sched_state detected stalls on CPUs/tasks: { 1} (detected by 0, t=420066 jiffies)
> [ 6241.410171] INFO: task mcelog:6513 blocked for more than 120 seconds.
>
> Reverting commit a4dd99250dc makes the stalls go away:
>
> rcu: create new rcu_access_index() and use in mce
>
> The MCE subsystem needs to sample an RCU-protected index outside of
> any protection for that index. If this was a pointer, we would use
> rcu_access_pointer(), but there is no corresponding rcu_access_index().
> This commit therefore creates an rcu_access_index() and applies it
> to MCE.
>
> Signed-off-by: Paul E. McKenney <[email protected]>
> Tested-by: Zdenek Kabelac <[email protected]>
Wow! This is just instructions, just wrapping the access in
ACCESS_ONCE().
Was the original RCU CPU stall repeatable?
Thanx, Paul
> Here's some bits from my config that might be relevant:
>
> # RCU Subsystem
> CONFIG_TREE_RCU=y
> # CONFIG_PREEMPT_RCU is not set
> # CONFIG_RCU_TRACE is not set
> CONFIG_RCU_FANOUT=64
> # CONFIG_RCU_FANOUT_EXACT is not set
> # CONFIG_RCU_FAST_NO_HZ is not set
> # CONFIG_TREE_RCU_TRACE is not set
> CONFIG_PREEMPT_NOTIFIERS=y
> # CONFIG_PREEMPT_NONE is not set
> CONFIG_PREEMPT_VOLUNTARY=y
> # CONFIG_PREEMPT is not set
> CONFIG_X86_MCE=y
> CONFIG_X86_MCE_INTEL=y
> CONFIG_X86_MCE_AMD=y
> CONFIG_X86_MCE_THRESHOLD=y
> # CONFIG_X86_MCE_INJECT is not set
> CONFIG_EDAC_DECODE_MCE=y
> # CONFIG_EDAC_MCE_INJ is not set
> CONFIG_EDAC_MCE=y
> # CONFIG_SPARSE_RCU_POINTER is not set
> # CONFIG_RCU_TORTURE_TEST is not set
> CONFIG_RCU_CPU_STALL_DETECTOR=y
> CONFIG_RCU_CPU_STALL_TIMEOUT=60
> CONFIG_RCU_CPU_STALL_DETECTOR_RUNNABLE=y
>
> Please let me know if there is anything I can do to help sort this out.
>
> -- Jim
>
Paul E. McKenney wrote:
> On Wed, Apr 27, 2011 at 01:59:01PM -0600, Jim Schutt wrote:
>> Hi,
>>
>> Testing 2.6.39-rc5 is giving me the following stall:
>>
>> [ 5767.731001] INFO: rcu_sched_state detected stall on CPU 1 (t=60001 jiffies)
>> [ 5767.732001] INFO: rcu_sched_state detected stalls on CPUs/tasks: { 1} (detected by 0, t=60002 jiffies)
>> [ 5947.763001] INFO: rcu_sched_state detected stall on CPU 1 (t=240032 jiffies)
>> [ 5947.764001] INFO: rcu_sched_state detected stalls on CPUs/tasks: { 1} (detected by 0, t=240034 jiffies)
>> [ 6024.489362] libceph: mon0 172.17.40.34:6789 socket closed
>> [ 6121.281139] INFO: task mcelog:6513 blocked for more than 120 seconds.
>> [ 6121.287575] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
>> [ 6121.295397] ffff880177aefce8 0000000000000082 ffffffff810339b6 ffff880226d35a40
>> [ 6121.302840] ffff88018226c3b0 ffff88018226c3b0 0000000000011e80 ffff880226d35a40
>> [ 6121.310284] ffff88018226c760 ffff880177aefe80 ffff880177aefd18 ffffffff813af047
>> [ 6121.317725] Call Trace:
>> [ 6121.320176] [<ffffffff810339b6>] ? calc_load_account_idle+0xe/0x1d
>> [ 6121.326437] [<ffffffff813af047>] schedule+0x159/0x193
>> [ 6121.331569] [<ffffffff813af449>] schedule_timeout+0x36/0xe2
>> [ 6121.337223] [<ffffffff810ad9eb>] ? trace_hardirqs_on+0x9/0x20
>> [ 6121.343047] [<ffffffff813aee2b>] do_wait_for_common+0x97/0xe3
>> [ 6121.348967] [<ffffffff8103e8fa>] ? try_to_wake_up+0x200/0x200
>> [ 6121.354794] [<ffffffff8107a4bf>] ? __raw_spin_lock_irq+0x17/0x2f
>> [ 6121.360878] [<ffffffff813af2a9>] wait_for_common+0x36/0x4d
>> [ 6121.366441] [<ffffffff813af378>] wait_for_completion+0x1d/0x1f
>> [ 6121.372356] [<ffffffff8109ae6d>] synchronize_sched+0x40/0x49
>> [ 6121.378096] [<ffffffff810635b8>] ? find_get_pid+0x1b/0x1b
>> [ 6121.383574] [<ffffffff81015fe5>] mce_read+0x17f/0x25d
>> [ 6121.388707] [<ffffffff81111af5>] ? rw_verify_area+0xac/0xdb
>> [ 6121.394358] [<ffffffff811121f1>] vfs_read+0xa9/0xe1
>> [ 6121.399317] [<ffffffff8111248d>] sys_read+0x4c/0x70
>> [ 6121.404278] [<ffffffff813b6deb>] system_call_fastpath+0x16/0x1b
>> [ 6127.795001] INFO: rcu_sched_state detected stall on CPU 1 (t=420064 jiffies)
>> [ 6127.796001] INFO: rcu_sched_state detected stalls on CPUs/tasks: { 1} (detected by 0, t=420066 jiffies)
>> [ 6241.410171] INFO: task mcelog:6513 blocked for more than 120 seconds.
>>
>> Reverting commit a4dd99250dc makes the stalls go away:
>>
>> rcu: create new rcu_access_index() and use in mce
>>
>> The MCE subsystem needs to sample an RCU-protected index outside of
>> any protection for that index. If this was a pointer, we would use
>> rcu_access_pointer(), but there is no corresponding rcu_access_index().
>> This commit therefore creates an rcu_access_index() and applies it
>> to MCE.
>>
>> Signed-off-by: Paul E. McKenney <[email protected]>
>> Tested-by: Zdenek Kabelac <[email protected]>
>
> Wow! This is just instructions, just wrapping the access in
> ACCESS_ONCE().
>
> Was the original RCU CPU stall repeatable?
Yes. I saw it on two different machines.
Both were running as Ceph clients, doing sustained
streaming writes, if that helps any.
I can attempt to repeat with any extra debugging
you'd like me to try.
-- Jim
>
> Thanx, Paul
>
>> Here's some bits from my config that might be relevant:
>>
>> # RCU Subsystem
>> CONFIG_TREE_RCU=y
>> # CONFIG_PREEMPT_RCU is not set
>> # CONFIG_RCU_TRACE is not set
>> CONFIG_RCU_FANOUT=64
>> # CONFIG_RCU_FANOUT_EXACT is not set
>> # CONFIG_RCU_FAST_NO_HZ is not set
>> # CONFIG_TREE_RCU_TRACE is not set
>> CONFIG_PREEMPT_NOTIFIERS=y
>> # CONFIG_PREEMPT_NONE is not set
>> CONFIG_PREEMPT_VOLUNTARY=y
>> # CONFIG_PREEMPT is not set
>> CONFIG_X86_MCE=y
>> CONFIG_X86_MCE_INTEL=y
>> CONFIG_X86_MCE_AMD=y
>> CONFIG_X86_MCE_THRESHOLD=y
>> # CONFIG_X86_MCE_INJECT is not set
>> CONFIG_EDAC_DECODE_MCE=y
>> # CONFIG_EDAC_MCE_INJ is not set
>> CONFIG_EDAC_MCE=y
>> # CONFIG_SPARSE_RCU_POINTER is not set
>> # CONFIG_RCU_TORTURE_TEST is not set
>> CONFIG_RCU_CPU_STALL_DETECTOR=y
>> CONFIG_RCU_CPU_STALL_TIMEOUT=60
>> CONFIG_RCU_CPU_STALL_DETECTOR_RUNNABLE=y
>>
>> Please let me know if there is anything I can do to help sort this out.
>>
>> -- Jim
>>
>
Jim Schutt wrote:
> Paul E. McKenney wrote:
>> On Wed, Apr 27, 2011 at 01:59:01PM -0600, Jim Schutt wrote:
>>> Hi,
>>>
>>> Testing 2.6.39-rc5 is giving me the following stall:
>>>
>>> [ 5767.731001] INFO: rcu_sched_state detected stall on CPU 1
>>> (t=60001 jiffies)
>>> [ 5767.732001] INFO: rcu_sched_state detected stalls on
>>> CPUs/tasks: { 1} (detected by 0, t=60002 jiffies)
>>> [ 5947.763001] INFO: rcu_sched_state detected stall on CPU 1
>>> (t=240032 jiffies)
>>> [ 5947.764001] INFO: rcu_sched_state detected stalls on
>>> CPUs/tasks: { 1} (detected by 0, t=240034 jiffies)
>>> [ 6024.489362] libceph: mon0 172.17.40.34:6789 socket closed
>>> [ 6121.281139] INFO: task mcelog:6513 blocked for more than 120
>>> seconds.
>>> [ 6121.287575] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs"
>>> disables this message.
>>> [ 6121.295397] ffff880177aefce8 0000000000000082
>>> ffffffff810339b6 ffff880226d35a40
>>> [ 6121.302840] ffff88018226c3b0 ffff88018226c3b0
>>> 0000000000011e80 ffff880226d35a40
>>> [ 6121.310284] ffff88018226c760 ffff880177aefe80
>>> ffff880177aefd18 ffffffff813af047
>>> [ 6121.317725] Call Trace:
>>> [ 6121.320176] [<ffffffff810339b6>] ?
>>> calc_load_account_idle+0xe/0x1d
>>> [ 6121.326437] [<ffffffff813af047>] schedule+0x159/0x193
>>> [ 6121.331569] [<ffffffff813af449>] schedule_timeout+0x36/0xe2
>>> [ 6121.337223] [<ffffffff810ad9eb>] ? trace_hardirqs_on+0x9/0x20
>>> [ 6121.343047] [<ffffffff813aee2b>] do_wait_for_common+0x97/0xe3
>>> [ 6121.348967] [<ffffffff8103e8fa>] ? try_to_wake_up+0x200/0x200
>>> [ 6121.354794] [<ffffffff8107a4bf>] ? __raw_spin_lock_irq+0x17/0x2f
>>> [ 6121.360878] [<ffffffff813af2a9>] wait_for_common+0x36/0x4d
>>> [ 6121.366441] [<ffffffff813af378>] wait_for_completion+0x1d/0x1f
>>> [ 6121.372356] [<ffffffff8109ae6d>] synchronize_sched+0x40/0x49
>>> [ 6121.378096] [<ffffffff810635b8>] ? find_get_pid+0x1b/0x1b
>>> [ 6121.383574] [<ffffffff81015fe5>] mce_read+0x17f/0x25d
>>> [ 6121.388707] [<ffffffff81111af5>] ? rw_verify_area+0xac/0xdb
>>> [ 6121.394358] [<ffffffff811121f1>] vfs_read+0xa9/0xe1
>>> [ 6121.399317] [<ffffffff8111248d>] sys_read+0x4c/0x70
>>> [ 6121.404278] [<ffffffff813b6deb>] system_call_fastpath+0x16/0x1b
>>> [ 6127.795001] INFO: rcu_sched_state detected stall on CPU 1
>>> (t=420064 jiffies)
>>> [ 6127.796001] INFO: rcu_sched_state detected stalls on
>>> CPUs/tasks: { 1} (detected by 0, t=420066 jiffies)
>>> [ 6241.410171] INFO: task mcelog:6513 blocked for more than 120
>>> seconds.
>>>
>>> Reverting commit a4dd99250dc makes the stalls go away:
>>>
>>> rcu: create new rcu_access_index() and use in mce
>>>
>>> The MCE subsystem needs to sample an RCU-protected index outside of
>>> any protection for that index. If this was a pointer, we would use
>>> rcu_access_pointer(), but there is no corresponding
>>> rcu_access_index().
>>> This commit therefore creates an rcu_access_index() and applies it
>>> to MCE.
>>>
>>> Signed-off-by: Paul E. McKenney <[email protected]>
>>> Tested-by: Zdenek Kabelac <[email protected]>
>>
>> Wow! This is just instructions, just wrapping the access in
>> ACCESS_ONCE().
>>
>> Was the original RCU CPU stall repeatable?
>
> Yes. I saw it on two different machines.
> Both were running as Ceph clients, doing sustained
> streaming writes, if that helps any.
>
> I can attempt to repeat with any extra debugging
> you'd like me to try.
Evidently I cannot reproduce this after all, so my revert
test was incorrect.
If I can learn how to reproduce this I'll post with details;
in the meantime ignore this, and sorry for the noise.
-- Jim
>
> -- Jim
>
>>
>> Thanx, Paul
>>
On Thu, Apr 28, 2011 at 10:06:57AM -0600, Jim Schutt wrote:
> Jim Schutt wrote:
> >Paul E. McKenney wrote:
> >>On Wed, Apr 27, 2011 at 01:59:01PM -0600, Jim Schutt wrote:
> >>>Hi,
> >>>
> >>>Testing 2.6.39-rc5 is giving me the following stall:
> >>>
> >>> [ 5767.731001] INFO: rcu_sched_state detected stall on CPU
> >>>1 (t=60001 jiffies)
> >>> [ 5767.732001] INFO: rcu_sched_state detected stalls on
> >>>CPUs/tasks: { 1} (detected by 0, t=60002 jiffies)
> >>> [ 5947.763001] INFO: rcu_sched_state detected stall on CPU
> >>>1 (t=240032 jiffies)
> >>> [ 5947.764001] INFO: rcu_sched_state detected stalls on
> >>>CPUs/tasks: { 1} (detected by 0, t=240034 jiffies)
> >>> [ 6024.489362] libceph: mon0 172.17.40.34:6789 socket closed
> >>> [ 6121.281139] INFO: task mcelog:6513 blocked for more
> >>>than 120 seconds.
> >>> [ 6121.287575] "echo 0 >
> >>>/proc/sys/kernel/hung_task_timeout_secs" disables this
> >>>message.
> >>> [ 6121.295397] ffff880177aefce8 0000000000000082
> >>>ffffffff810339b6 ffff880226d35a40
> >>> [ 6121.302840] ffff88018226c3b0 ffff88018226c3b0
> >>>0000000000011e80 ffff880226d35a40
> >>> [ 6121.310284] ffff88018226c760 ffff880177aefe80
> >>>ffff880177aefd18 ffffffff813af047
> >>> [ 6121.317725] Call Trace:
> >>> [ 6121.320176] [<ffffffff810339b6>] ?
> >>>calc_load_account_idle+0xe/0x1d
> >>> [ 6121.326437] [<ffffffff813af047>] schedule+0x159/0x193
> >>> [ 6121.331569] [<ffffffff813af449>] schedule_timeout+0x36/0xe2
> >>> [ 6121.337223] [<ffffffff810ad9eb>] ? trace_hardirqs_on+0x9/0x20
> >>> [ 6121.343047] [<ffffffff813aee2b>] do_wait_for_common+0x97/0xe3
> >>> [ 6121.348967] [<ffffffff8103e8fa>] ? try_to_wake_up+0x200/0x200
> >>> [ 6121.354794] [<ffffffff8107a4bf>] ? __raw_spin_lock_irq+0x17/0x2f
> >>> [ 6121.360878] [<ffffffff813af2a9>] wait_for_common+0x36/0x4d
> >>> [ 6121.366441] [<ffffffff813af378>] wait_for_completion+0x1d/0x1f
> >>> [ 6121.372356] [<ffffffff8109ae6d>] synchronize_sched+0x40/0x49
> >>> [ 6121.378096] [<ffffffff810635b8>] ? find_get_pid+0x1b/0x1b
> >>> [ 6121.383574] [<ffffffff81015fe5>] mce_read+0x17f/0x25d
> >>> [ 6121.388707] [<ffffffff81111af5>] ? rw_verify_area+0xac/0xdb
> >>> [ 6121.394358] [<ffffffff811121f1>] vfs_read+0xa9/0xe1
> >>> [ 6121.399317] [<ffffffff8111248d>] sys_read+0x4c/0x70
> >>> [ 6121.404278] [<ffffffff813b6deb>] system_call_fastpath+0x16/0x1b
> >>> [ 6127.795001] INFO: rcu_sched_state detected stall on CPU
> >>>1 (t=420064 jiffies)
> >>> [ 6127.796001] INFO: rcu_sched_state detected stalls on
> >>>CPUs/tasks: { 1} (detected by 0, t=420066 jiffies)
> >>> [ 6241.410171] INFO: task mcelog:6513 blocked for more
> >>>than 120 seconds.
> >>>
> >>>Reverting commit a4dd99250dc makes the stalls go away:
> >>>
> >>> rcu: create new rcu_access_index() and use in mce
> >>>
> >>> The MCE subsystem needs to sample an RCU-protected index outside of
> >>> any protection for that index. If this was a pointer, we would use
> >>> rcu_access_pointer(), but there is no corresponding
> >>>rcu_access_index().
> >>> This commit therefore creates an rcu_access_index() and applies it
> >>> to MCE.
> >>>
> >>> Signed-off-by: Paul E. McKenney <[email protected]>
> >>> Tested-by: Zdenek Kabelac <[email protected]>
> >>
> >>Wow! This is just instructions, just wrapping the access in
> >>ACCESS_ONCE().
> >>
> >>Was the original RCU CPU stall repeatable?
> >
> >Yes. I saw it on two different machines.
> >Both were running as Ceph clients, doing sustained
> >streaming writes, if that helps any.
> >
> >I can attempt to repeat with any extra debugging
> >you'd like me to try.
>
> Evidently I cannot reproduce this after all, so my revert
> test was incorrect.
>
> If I can learn how to reproduce this I'll post with details;
> in the meantime ignore this, and sorry for the noise.
OK -- I must confess that I could not understand how this change
could cause the problem! ;-)
Thanx, Paul