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perf: Add cond_resched() to task_function_call()

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Under rare circumstances, task_function_call() can repeatedly fail and
cause a soft lockup.

There is a slight race where the process is no longer running on the cpu
we targeted by the time remote_function() runs.  The code will simply
try again.  If we are very unlucky, this will continue to fail, until a
watchdog fires.  This can happen in a heavily loaded, multi-core virtual
machine.

Reported-by: syzbot+bb4935a5c09b5ff79940@syzkaller.appspotmail.com
Signed-off-by: Barret Rhoden <brho@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200414222920.121401-1-brho@google.com
This commit is contained in:
Barret Rhoden 2020-04-14 18:29:20 -04:00 committed by Peter Zijlstra
parent 3a4ac121c2
commit 2ed6edd33a
1 changed files with 14 additions and 9 deletions
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23
kernel/events/core.c
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@ -95,11 +95,11 @@ static void remote_function(void *data)
* @info: the function call argument
*
* Calls the function @func when the task is currently running. This might
* be on the current CPU, which just calls the function directly
* be on the current CPU, which just calls the function directly. This will
* retry due to any failures in smp_call_function_single(), such as if the
* task_cpu() goes offline concurrently.
*
* returns: @func return value, or
* -ESRCH - when the process isn't running
* -EAGAIN - when the process moved away
* returns @func return value or -ESRCH when the process isn't running
*/
static int
task_function_call(struct task_struct *p, remote_function_f func, void *info)
@ -112,11 +112,16 @@ task_function_call(struct task_struct *p, remote_function_f func, void *info)
};
int ret;
do {
ret = smp_call_function_single(task_cpu(p), remote_function, &data, 1);
if (!ret)
ret = data.ret;
} while (ret == -EAGAIN);
for (;;) {
ret = smp_call_function_single(task_cpu(p), remote_function,
&data, 1);
ret = !ret ? data.ret : -EAGAIN;
if (ret != -EAGAIN)
break;
cond_resched();
}
return ret;
}