Messages in this thread | | | Date | Sun, 18 Jan 2015 15:13:21 +0100 | From | Ingo Molnar <> | Subject | Re: perf fuzzer crash [PATCH] perf: Get group events reference before moving the group |
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* Peter Zijlstra <peterz@infradead.org> wrote:
> --- a/kernel/events/core.c > +++ b/kernel/events/core.c > @@ -42,6 +42,7 @@ > #include <linux/module.h> > #include <linux/mman.h> > #include <linux/compat.h> > +#include <linux/percpu-rwsem.h> > > #include "internal.h" > > @@ -122,6 +123,42 @@ static int cpu_function_call(int cpu, int (*func) (void *info), void *info) > return data.ret; > } > > +/* > + * Required to migrate events between contexts. > + * > + * Migrating events between contexts is rather tricky; there is no real > + * serialization around the perf_event::ctx pointer. > + * > + * So what we do is hold this rwsem over the remove_from_context and > + * install_in_context. The remove_from_context ensures the event is inactive > + * and will not be used from IRQ/NMI context anymore, and the remaining > + * sites can acquire the rwsem read side. > + */ > +static struct percpu_rw_semaphore perf_rwsem; > + > +static inline struct perf_event_context *perf_event_ctx(struct perf_event *event) > +{ > +#ifdef CONFIG_LOCKDEP > + /* > + * Assert the locking rules outlined above; in order to dereference > + * event->ctx we must either be attached to the context or hold > + * perf_rwsem. > + * > + * XXX not usable from IPIs because the lockdep held lock context > + * will be wrong; maybe add trylock variants to the percpu_rw_semaphore > + */ > + WARN_ON_ONCE(!(event->attach_state & PERF_ATTACH_CONTEXT) || > + (debug_locks && !lockdep_is_held(&perf_rwsem.rw_sem))); > +#endif > + > + return event->ctx; > +} > + > +static inline struct perf_event_context *__perf_event_ctx(struct perf_event *event) > +{ > + return event->ctx; > +}
So if this approach is acceptable I'd also rename event->ctx to event->__ctx, to make sure it's not used accidentally without serialization in any old (or new) perf related patches.
Thanks,
Ingo
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