Messages in this thread Patch in this message | | | Date | Thu, 13 Sep 2018 09:46:07 +0200 | From | Jiri Olsa <> | Subject | Re: [PATCH] perf: Prevent recursion in ring buffer |
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On Thu, Sep 13, 2018 at 09:07:40AM +0200, Peter Zijlstra wrote: > On Wed, Sep 12, 2018 at 09:33:17PM +0200, Jiri Olsa wrote: > > Some of the scheduling tracepoints allow the perf_tp_event > > code to write to ring buffer under different cpu than the > > code is running on. > > ARGH.. that is indeed borken. > > > diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c > > index 4a9937076331..0c976ac414c5 100644 > > --- a/kernel/events/ring_buffer.c > > +++ b/kernel/events/ring_buffer.c > > @@ -101,6 +101,7 @@ static void perf_output_put_handle(struct perf_output_handle *handle) > > > > out: > > preempt_enable(); > > + atomic_set(&rb->recursion, 0); > > } > > > > static __always_inline bool > > @@ -145,6 +146,12 @@ __perf_output_begin(struct perf_output_handle *handle, > > goto out; > > } > > > > + if (atomic_cmpxchg(&rb->recursion, 0, 1) != 0) { > > + if (rb->nr_pages) > > + local_inc(&rb->lost); > > + goto out; > > + } > > + > > handle->rb = rb; > > handle->event = event; > > > > @@ -286,6 +293,7 @@ ring_buffer_init(struct ring_buffer *rb, long watermark, int flags) > > rb->overwrite = 1; > > > > atomic_set(&rb->refcount, 1); > > + atomic_set(&rb->recursion, 0); > > > > INIT_LIST_HEAD(&rb->event_list); > > spin_lock_init(&rb->event_lock); > > That's not a recursion count, that's a test-and-set spinlock, and you > got the memory ordering wrong for that. > > Also, we tried very hard to avoid atomic ops in the ring-buffer and you > just wrecked that. Worse, you wrecked previously working interrupt > nesting output. > > Let me have a look at this.
I was first thinking to just leave it on the current cpu, but not sure current users would be ok with that ;-)
jirka
--- diff --git a/kernel/events/core.c b/kernel/events/core.c index abaed4f8bb7f..9b534a2ecf17 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -8308,6 +8308,8 @@ void perf_tp_event(u16 event_type, u64 count, void *record, int entry_size, continue; if (event->attr.config != entry->type) continue; + if (event->cpu != smp_processor_id()) + continue; if (perf_tp_event_match(event, &data, regs)) perf_swevent_event(event, count, &data, regs); }
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