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authorPeter Zijlstra <peterz@infradead.org>2013-07-12 11:08:33 +0200
committerIngo Molnar <mingo@kernel.org>2013-07-12 11:11:09 +0200
commit058ebd0eba3aff16b144eabf4510ed9510e1416e (patch)
tree1e35463a05e5b6109baf409a947d661a638d140b /kernel/events
parent06f417968beac6e6b614e17b37d347aa6a6b1d30 (diff)
downloadblackbird-op-linux-058ebd0eba3aff16b144eabf4510ed9510e1416e.tar.gz
blackbird-op-linux-058ebd0eba3aff16b144eabf4510ed9510e1416e.zip
perf: Fix perf_lock_task_context() vs RCU
Jiri managed to trigger this warning: [] ====================================================== [] [ INFO: possible circular locking dependency detected ] [] 3.10.0+ #228 Tainted: G W [] ------------------------------------------------------- [] p/6613 is trying to acquire lock: [] (rcu_node_0){..-...}, at: [<ffffffff810ca797>] rcu_read_unlock_special+0xa7/0x250 [] [] but task is already holding lock: [] (&ctx->lock){-.-...}, at: [<ffffffff810f2879>] perf_lock_task_context+0xd9/0x2c0 [] [] which lock already depends on the new lock. [] [] the existing dependency chain (in reverse order) is: [] [] -> #4 (&ctx->lock){-.-...}: [] -> #3 (&rq->lock){-.-.-.}: [] -> #2 (&p->pi_lock){-.-.-.}: [] -> #1 (&rnp->nocb_gp_wq[1]){......}: [] -> #0 (rcu_node_0){..-...}: Paul was quick to explain that due to preemptible RCU we cannot call rcu_read_unlock() while holding scheduler (or nested) locks when part of the read side critical section was preemptible. Therefore solve it by making the entire RCU read side non-preemptible. Also pull out the retry from under the non-preempt to play nice with RT. Reported-by: Jiri Olsa <jolsa@redhat.com> Helped-out-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: <stable@kernel.org> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel/events')
-rw-r--r--kernel/events/core.c15
1 files changed, 14 insertions, 1 deletions
diff --git a/kernel/events/core.c b/kernel/events/core.c
index ef5e7cc686e3..eba8fb5834ae 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -947,8 +947,18 @@ perf_lock_task_context(struct task_struct *task, int ctxn, unsigned long *flags)
{
struct perf_event_context *ctx;
- rcu_read_lock();
retry:
+ /*
+ * One of the few rules of preemptible RCU is that one cannot do
+ * rcu_read_unlock() while holding a scheduler (or nested) lock when
+ * part of the read side critical section was preemptible -- see
+ * rcu_read_unlock_special().
+ *
+ * Since ctx->lock nests under rq->lock we must ensure the entire read
+ * side critical section is non-preemptible.
+ */
+ preempt_disable();
+ rcu_read_lock();
ctx = rcu_dereference(task->perf_event_ctxp[ctxn]);
if (ctx) {
/*
@@ -964,6 +974,8 @@ retry:
raw_spin_lock_irqsave(&ctx->lock, *flags);
if (ctx != rcu_dereference(task->perf_event_ctxp[ctxn])) {
raw_spin_unlock_irqrestore(&ctx->lock, *flags);
+ rcu_read_unlock();
+ preempt_enable();
goto retry;
}
@@ -973,6 +985,7 @@ retry:
}
}
rcu_read_unlock();
+ preempt_enable();
return ctx;
}
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