events: Protect access via task_subsys_state_check()
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 <ajax@redhat.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: a.p.zijlstra@chello.nl
Cc: paulus@samba.org
Cc: acme@ghostprotocols.net
Link: http://lkml.kernel.org/r/20130419190124.GA8638@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Tested-by: Gustavo Luiz Duarte <gusld@br.ibm.com>
projects / ~andy / linux / commit