From: Paul E. McKenney <paul...@linux.vnet.ibm.com>
The following RCU splat indicates lack of RCU protection:
[ 953.267649] ===============================
[ 953.267652] [ INFO: suspicious RCU usage. ]
[ 953.267657] 3.9.0-0.rc6.git2.4.fc19.ppc64p7 #1 Not tainted
[ 953.267661] -------------------------------
[ 953.267664] include/linux/cgroup.h:534 suspicious rcu_dereference_check()
usage!
[ 953.267669]
[ 953.267669] other info that might help us debug this:
[ 953.267669]
[ 953.267675]
[ 953.267675] rcu_scheduler_active = 1, debug_locks = 0
[ 953.267680] 1 lock held by glxgears/1289:
[ 953.267683] #0: (&sig->cred_guard_mutex){+.+.+.}, at: [<c00000000027f884>]
.prepare_bprm_creds+0x34/0xa0
[ 953.267700]
[ 953.267700] stack backtrace:
[ 953.267704] Call Trace:
[ 953.267709] [c0000001f0d1b6e0] [c000000000016e30] .show_stack+0x130/0x200
(unreliable)
[ 953.267717] [c0000001f0d1b7b0] [c0000000001267f8]
.lockdep_rcu_suspicious+0x138/0x180
[ 953.267724] [c0000001f0d1b840] [c0000000001d43a4]
.perf_event_comm+0x4c4/0x690
[ 953.267731] [c0000001f0d1b950] [c00000000027f6e4] .set_task_comm+0x84/0x1f0
[ 953.267737] [c0000001f0d1b9f0] [c000000000280414] .setup_new_exec+0x94/0x220
[ 953.267744] [c0000001f0d1ba70] [c0000000002f665c]
.load_elf_binary+0x58c/0x19b0
...
This commit therefore adds the required RCU read-side critical
section to perf_event_comm().
Reported-by: Adam Jackson <a...@redhat.com>
Signed-off-by: Paul E. McKenney <paul...@linux.vnet.ibm.com>
Cc: a.p.zijls...@chello.nl
Cc: pau...@samba.org
Cc: a...@ghostprotocols.net
Link: http://lkml.kernel.org/r/20130419190124.ga8...@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mi...@kernel.org>
Tested-by: Gustavo Luiz Duarte <gu...@br.ibm.com>
---
kernel/events/core.c | 2 ++
1 files changed, 2 insertions(+), 0 deletions(-)
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 4d3124b..9fcb094 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -4596,6 +4596,7 @@ void perf_event_comm(struct task_struct *task)
struct perf_event_context *ctx;
int ctxn;
+ rcu_read_lock();
for_each_task_context_nr(ctxn) {
ctx = task->perf_event_ctxp[ctxn];
if (!ctx)
@@ -4603,6 +4604,7 @@ void perf_event_comm(struct task_struct *task)
perf_event_enable_on_exec(ctx);
}
+ rcu_read_unlock();
if (!atomic_read(&nr_comm_events))
return;
--
1.7.1
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