Messages in this thread | | | Date | Tue, 9 Apr 2024 15:33:36 +0200 | From | Sebastian Andrzej Siewior <> | Subject | Re: [PATCH v3 3/4] perf: Remove perf_swevent_get_recursion_context() from perf_pending_task(). |
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On 2024-04-09 14:00:49 [+0200], Frederic Weisbecker wrote: > Le Tue, Apr 09, 2024 at 12:54:05PM +0200, Sebastian Andrzej Siewior a écrit : > > On 2024-04-09 12:35:46 [+0200], Frederic Weisbecker wrote: > > > > > > @@ -6800,10 +6792,6 @@ static void perf_pending_task(struct callback_head *head) > > > > > > local_dec(&event->ctx->nr_pending); > > > > > > } > > > > > > > > > > > > - if (rctx >= 0) > > > > > > - perf_swevent_put_recursion_context(rctx); > > > > > > - preempt_enable_notrace(); > > > > > > > > > > Well, if a software event happens during perf_sigtrap(), the task work > > > > > may be requeued endlessly and the task may get stuck in task_work_run()... > > > > > > > > The last time I checked it had no users in the task context. How would > > > > that happen? > > > > > > I guess many tracepoint events would do the trick. Such as trace_lock_acquire() > > > for example. > > > > So the perf_trace_buf_alloc() is invoked from that trace point and > > avoids the recursion. And any trace event from within perf_sigtrap() > > would trigger the endless loop? > > No sure I'm following: > > 1) event->perf_event_overflow() -> task_work_add() > //return to userspace > 2) task_work_run() -> perf_pending_task() -> perf_sigtrap() -> tracepoint event > -> perf_event_overflow() -> task_work_add() > 3) task_work_run() -> perf_pending_task() -> etc... > > What am I missing?
Yes, that is what I tried to say. Anyway, I misunderstood the concept before. That means we need to keep that counter here and a migrate_disable() is needed to avoid CPU migration which is sad.
> Thanks.
Sebastian
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