[PATCH 3.13 158/163] perf: fix perf bug in fork()

From: Kamal Mostafa
Date: Thu Oct 09 2014 - 17:12:14 EST -stable review patch. If anyone has any objections, please let me know.


From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>

commit 6c72e3501d0d62fc064d3680e5234f3463ec5a86 upstream.

Oleg noticed that a cleanup by Sylvain actually uncovered a bug; by
calling perf_event_free_task() when failing sched_fork() we will not yet
have done the memset() on ->perf_event_ctxp[] and will therefore try and
'free' the inherited contexts, which are still in use by the parent
process. This is bad..

Suggested-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Reported-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Reported-by: Sylvain 'ythier' Hitier <sylvain.hitier@xxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Kamal Mostafa <kamal@xxxxxxxxxxxxx>
kernel/events/core.c | 4 +++-
kernel/fork.c | 5 +++--
2 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 38f0d1b..6acd7d9 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -7808,8 +7808,10 @@ int perf_event_init_task(struct task_struct *child)

for_each_task_context_nr(ctxn) {
ret = perf_event_init_context(child, ctxn);
- if (ret)
+ if (ret) {
+ perf_event_free_task(child);
return ret;
+ }

return 0;
diff --git a/kernel/fork.c b/kernel/fork.c
index d0ca776..5726bf1 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1323,7 +1323,7 @@ static struct task_struct *copy_process(unsigned long clone_flags,
goto bad_fork_cleanup_policy;
retval = audit_alloc(p);
if (retval)
- goto bad_fork_cleanup_policy;
+ goto bad_fork_cleanup_perf;
/* copy all the process information */
retval = copy_semundo(clone_flags, p);
if (retval)
@@ -1522,8 +1522,9 @@ bad_fork_cleanup_semundo:

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