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Commit2ed6edd

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Barret RhodenPeter Zijlstra
Barret Rhoden
authored and
Peter Zijlstra
committed
perf: Add cond_resched() to task_function_call()
Under rare circumstances, task_function_call() can repeatedly fail andcause a soft lockup.There is a slight race where the process is no longer running on the cpuwe targeted by the time remote_function() runs. The code will simplytry again. If we are very unlucky, this will continue to fail, until awatchdog fires. This can happen in a heavily loaded, multi-core virtualmachine.Reported-by: syzbot+bb4935a5c09b5ff79940@syzkaller.appspotmail.comSigned-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
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‎kernel/events/core.c‎

Lines changed: 14 additions & 9 deletions
Original file line numberDiff line numberDiff line change
@@ -95,11 +95,11 @@ static void remote_function(void *data)
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* @info:the function call argument
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*
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* Calls the function @func when the task is currently running. This might
98-
* be on the current CPU, which just calls the function directly
98+
* be on the current CPU, which just calls the function directly. This will
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* retry due to any failures in smp_call_function_single(), such as if the
100+
* task_cpu() goes offline concurrently.
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*
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* returns: @func return value, or
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* -ESRCH - when the process isn't running
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* -EAGAIN - when the process moved away
102+
* returns @func return value or -ESRCH when the process isn't running
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*/
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staticint
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task_function_call(structtask_struct*p,remote_function_ffunc,void*info)
@@ -112,11 +112,16 @@ task_function_call(struct task_struct *p, remote_function_f func, void *info)
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};
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intret;
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do {
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ret=smp_call_function_single(task_cpu(p),remote_function,&data,1);
117-
if (!ret)
118-
ret=data.ret;
119-
}while (ret==-EAGAIN);
115+
for (;;) {
116+
ret=smp_call_function_single(task_cpu(p),remote_function,
117+
&data,1);
118+
ret= !ret ?data.ret :-EAGAIN;
119+
120+
if (ret!=-EAGAIN)
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break;
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cond_resched();
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}
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returnret;
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}

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