lkml.org 
[lkml]   [2012]   [Sep]   [6]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH tip/core/rcu 11/15] rcu: Avoid spurious RCU CPU stall warnings
From
Date
On Thu, 2012-09-06 at 14:03 -0700, Paul E. McKenney wrote:

> Here are a few other ways that stalls can happen:
>
> o A CPU looping in an RCU read-side critical section.

For a minute? That's a bug.

>
> o A CPU looping with interrupts disabled. This condition can
> result in RCU-sched and RCU-bh stalls.

Also a bug.

>
> o A CPU looping with preemption disabled. This condition can
> result in RCU-sched stalls and, if ksoftirqd is in use, RCU-bh
> stalls.

Bug as well.

>
> o A CPU looping with bottom halves disabled. This condition can
> result in RCU-sched and RCU-bh stalls.

Bug too.

>
> o For !CONFIG_PREEMPT kernels, a CPU looping anywhere in the kernel
> without invoking schedule().

Another bug.

>
> o A CPU-bound real-time task in a CONFIG_PREEMPT kernel, which might
> happen to preempt a low-priority task in the middle of an RCU
> read-side critical section. This is especially damaging if
> that low-priority task is not permitted to run on any other CPU,
> in which case the next RCU grace period can never complete, which
> will eventually cause the system to run out of memory and hang.
> While the system is in the process of running itself out of
> memory, you might see stall-warning messages.

Buggy system.

>
> o A CPU-bound real-time task in a CONFIG_PREEMPT_RT kernel that
> is running at a higher priority than the RCU softirq threads.
> This will prevent RCU callbacks from ever being invoked,
> and in a CONFIG_TREE_PREEMPT_RCU kernel will further prevent
> RCU grace periods from ever completing. Either way, the
> system will eventually run out of memory and hang. In the
> CONFIG_TREE_PREEMPT_RCU case, you might see stall-warning
> messages.

Not really a bug, but the developers need a spanking.

>
> o A hardware or software issue shuts off the scheduler-clock
> interrupt on a CPU that is not in dyntick-idle mode. This
> problem really has happened, and seems to be most likely to
> result in RCU CPU stall warnings for CONFIG_NO_HZ=n kernels.

Driving the bug.

>
> o A bug in the RCU implementation.

Bug in the name.

>
> o A hardware failure. This is quite unlikely, but has occurred
> at least once in real life. A CPU failed in a running system,
> becoming unresponsive, but not causing an immediate crash.
> This resulted in a series of RCU CPU stall warnings, eventually
> leading the realization that the CPU had failed.

Hardware bug.

So, where's the "spurious RCU CPU stall warnings"?

All these cases deserve a warning.

-- Steve




\
 
 \ /
  Last update: 2012-09-07 00:21    [W:0.110 / U:0.136 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site