Messages in this thread Patch in this message | | | Date | Tue, 14 Apr 2020 15:03:51 -0400 | Subject | perf: add cond_resched() to task_function_call() | From | Barret Rhoden <> |
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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> --- kernel/events/core.c | 12 ++++++++---- 1 file changed, 8 insertions(+), 4 deletions(-)
diff --git a/kernel/events/core.c b/kernel/events/core.c index 55e44417f66d..65c2c05e24c2 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -99,7 +99,7 @@ static void remote_function(void *data) * * returns: @func return value, or * -ESRCH - when the process isn't running - * -EAGAIN - when the process moved away + * -ENXIO - when the cpu the process was on has gone offline */ static int task_function_call(struct task_struct *p, remote_function_f func, void *info) @@ -112,11 +112,15 @@ 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); + while (1) { + ret = smp_call_function_single(task_cpu(p), remote_function, + &data, 1); if (!ret) ret = data.ret; - } while (ret == -EAGAIN); + if (ret != -EAGAIN) + break; + cond_resched(); + } return ret; } -- 2.26.0.110.g2183baf09c-goog
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