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authorOleg Nesterov <oleg@redhat.com>2015-05-30 22:04:25 +0200
committerIngo Molnar <mingo@kernel.org>2015-06-19 09:38:45 +0200
commit2f993cf093643b98477c421fa2b9a98dcc940323 (patch)
treec9c0dd52b28e7ae4b8f10a76ee2196df0277561d
parent17fda38f15953c398a2a0ae427928873c5c8c47c (diff)
perf: Fix ring_buffer_attach() RCU sync, again
While looking for other users of get_state/cond_sync. I Found ring_buffer_attach() and it looks obviously buggy? Don't we need to ensure that we have "synchronize" _between_ list_del() and list_add() ? IOW. Suppose that ring_buffer_attach() preempts right_after get_state_synchronize_rcu() and gp completes before spin_lock(). In this case cond_synchronize_rcu() does nothing and we reuse ->rb_entry without waiting for gp in between? It also moves the ->rcu_pending check under "if (rb)", to make it more readable imo. Signed-off-by: Oleg Nesterov <oleg@redhat.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Andy Lutomirski <luto@amacapital.net> Cc: Borislav Petkov <bp@alien8.de> Cc: Brian Gerst <brgerst@gmail.com> Cc: Denys Vlasenko <dvlasenk@redhat.com> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: dave@stgolabs.net Cc: der.herr@hofr.at Cc: josh@joshtriplett.org Cc: tj@kernel.org Fixes: b69cf53640da ("perf: Fix a race between ring_buffer_detach() and ring_buffer_attach()") Link: http://lkml.kernel.org/r/20150530200425.GA15748@redhat.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
-rw-r--r--kernel/events/core.c14
1 files changed, 7 insertions, 7 deletions
diff --git a/kernel/events/core.c b/kernel/events/core.c
index eddf1ed4155e..0ceb386777ae 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -4331,20 +4331,20 @@ static void ring_buffer_attach(struct perf_event *event,
WARN_ON_ONCE(event->rcu_pending);
old_rb = event->rb;
- event->rcu_batches = get_state_synchronize_rcu();
- event->rcu_pending = 1;
-
spin_lock_irqsave(&old_rb->event_lock, flags);
list_del_rcu(&event->rb_entry);
spin_unlock_irqrestore(&old_rb->event_lock, flags);
- }
- if (event->rcu_pending && rb) {
- cond_synchronize_rcu(event->rcu_batches);
- event->rcu_pending = 0;
+ event->rcu_batches = get_state_synchronize_rcu();
+ event->rcu_pending = 1;
}
if (rb) {
+ if (event->rcu_pending) {
+ cond_synchronize_rcu(event->rcu_batches);
+ event->rcu_pending = 0;
+ }
+
spin_lock_irqsave(&rb->event_lock, flags);
list_add_rcu(&event->rb_entry, &rb->event_list);
spin_unlock_irqrestore(&rb->event_lock, flags);