Messages in this thread | | | Date | Tue, 16 Aug 2022 17:39:54 +0100 | From | Mark Rutland <> | Subject | Re: [PATCH v3] perf/core: Fix reentry problem in perf_output_read_group |
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On Tue, Aug 16, 2022 at 05:31:27PM +0200, Peter Zijlstra wrote: > On Tue, Aug 16, 2022 at 03:54:19PM +0100, Mark Rutland wrote: > > > diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h > > > index ee8b9ecdc03b..d4d53b9ba71e 100644 > > > --- a/include/linux/perf_event.h > > > +++ b/include/linux/perf_event.h > > > @@ -631,7 +631,12 @@ struct pmu_event_list { > > > struct list_head list; > > > }; > > > > > > +/* > > > + * Iterating the sibling list requires this list to be stable; by ensuring IRQs > > > + * are disabled IPIs from perf_{install_in,remove_from}_context() are held off. > > > + */ > > > #define for_each_sibling_event(sibling, event) \ > > > + lockdep_assert_irqs_disabled(); \ > > > if ((event)->group_leader == (event)) \ > > > list_for_each_entry((sibling), &(event)->sibling_list, sibling_list) > > > > > > > I had a go with v6.0-rc1 and Vince's perf fuzzer immediately triggered a bunch > > of cases (dump below). > > > > I had thought holding the context mutex protected some of these cases, even > > with IRQs unmasked? > > Ah yes.. duh. How's this then? > > > diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h > index ee8b9ecdc03b..4d9cf508c510 100644 > --- a/include/linux/perf_event.h > +++ b/include/linux/perf_event.h > @@ -631,7 +631,21 @@ struct pmu_event_list { > struct list_head list; > }; > > +#ifdef CONFIG_LOCKDEP > +#define LOCKDEP_ASSERT_EVENT_CTX(event) \ > + WARN_ON_ONCE(__lockdep_enabled && \ > + (this_cpu_read(hardirqs_enabled) || \ > + lockdep_is_held(&(event)->ctx->mutex) != LOCK_STATE_HELD))
Uh, should that `||` be `&&`, or am I missing the plot?
This'll warn if IRQs are enabled regardless of whether the mutex is held.
Thanks, Mark.
> +#else > +#define LOCKDEP_ASSERT_EVENT_CTX(event) > +#endif > + > +/* > + * Iterating the sibling list requires this list to be stable; by ensuring IRQs > + * are disabled IPIs from perf_{install_in,remove_from}_context() are held off. > + */ > #define for_each_sibling_event(sibling, event) \ > + LOCKDEP_ASSERT_EVENT_CTX(event); \ > if ((event)->group_leader == (event)) \ > list_for_each_entry((sibling), &(event)->sibling_list, sibling_list) >
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