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

Kamal Mostafa kamal at canonical.com
Thu Oct 9 21:03:03 UTC 2014 -stable review patch.  If anyone has any objections, please let me know.


From: Peter Zijlstra <peterz at infradead.org>

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 at redhat.com>
Reported-by: Oleg Nesterov <oleg at redhat.com>
Reported-by: Sylvain 'ythier' Hitier <sylvain.hitier at gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz at infradead.org>
Cc: Ingo Molnar <mingo at kernel.org>
Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
 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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