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Commit e81b05e5 authored by Barret Rhoden's avatar Barret Rhoden Committed by Greg Kroah-Hartman
Browse files

perf: Add cond_resched() to task_function_call() 



commit 2ed6edd33a214bca02bd2b45e3fc3038a059436b upstream.

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: default avatar <syzbot+bb4935a5c09b5ff79940@syzkaller.appspotmail.com>
Signed-off-by: default avatarBarret Rhoden <brho@google.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200414222920.121401-1-brho@google.com


Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent e0544273

kernel/events/core.c

+14 −9
Original line number Diff line number Diff line
@@ -93,11 +93,11 @@ 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)
@@ -110,11 +110,16 @@ 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;

}