From b91fc39f4ad7503419dd617df78401fa36266cb3 Mon Sep 17 00:00:00 2001 From: Arnaldo Carvalho de Melo Date: Mon, 6 Apr 2015 20:43:22 -0300 Subject: perf machine: Protect the machine->threads with a rwlock In addition to using refcounts for the struct thread lifetime management, we need to protect access to machine->threads from concurrent access. That happens in 'perf top', where a thread processes events, inserting and deleting entries from that rb_tree while another thread decays hist_entries, that end up dropping references and ultimately deleting threads from the rb_tree and releasing its resources when no further hist_entry (or other data structures, like in 'perf sched') references it. So the rule is the same for refcounts + protected trees in the kernel, get the tree lock, find object, bump the refcount, drop the tree lock, return, use object, drop the refcount if no more use of it is needed, keep it if storing it in some other data structure, drop when releasing that data structure. I.e. pair "t = machine__find(new)_thread()" with a "thread__put(t)", and "perf_event__preprocess_sample(&al)" with "addr_location__put(&al)". The addr_location__put() one is because as we return references to several data structures, we may end up adding more reference counting for the other data structures and then we'll drop it at addr_location__put() time. Acked-by: David Ahern Cc: Adrian Hunter Cc: Borislav Petkov Cc: Don Zickus Cc: Frederic Weisbecker Cc: Jiri Olsa Cc: Namhyung Kim Cc: Stephane Eranian Link: http://lkml.kernel.org/n/tip-bs9rt4n0jw3hi9f3zxyy3xln@git.kernel.org Signed-off-by: Arnaldo Carvalho de Melo --- tools/perf/util/event.c | 15 +++++++++++++++ 1 file changed, 15 insertions(+) (limited to 'tools/perf/util/event.c') diff --git a/tools/perf/util/event.c b/tools/perf/util/event.c index db526091f580..a513a51f7330 100644 --- a/tools/perf/util/event.c +++ b/tools/perf/util/event.c @@ -919,6 +919,10 @@ void thread__find_addr_location(struct thread *thread, al->sym = NULL; } +/* + * Callers need to drop the reference to al->thread, obtained in + * machine__findnew_thread() + */ int perf_event__preprocess_sample(const union perf_event *event, struct machine *machine, struct addr_location *al, @@ -979,6 +983,17 @@ int perf_event__preprocess_sample(const union perf_event *event, return 0; } +/* + * The preprocess_sample method will return with reference counts for the + * in it, when done using (and perhaps getting ref counts if needing to + * keep a pointer to one of those entries) it must be paired with + * addr_location__put(), so that the refcounts can be decremented. + */ +void addr_location__put(struct addr_location *al) +{ + thread__zput(al->thread); +} + bool is_bts_event(struct perf_event_attr *attr) { return attr->type == PERF_TYPE_HARDWARE && -- cgit v1.2.3