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Subject[PATCH 2/2] perf: fix perf_event_init_task()/perf_event_free_task() interaction
perf_event_init_task() should clear child->perf_event_ctxp[] before
anything else. Otherwise, if perf_event_init_context(perf_hw_context)
fails, perf_event_free_task() can free perf_event_ctxp[perf_sw_context]
copied from parent->perf_event_ctxp[] by dup_task_struct().

Also move the initialization of perf_event_mutex and perf_event_list
from perf_event_init_context() to perf_event_init_context().

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---

kernel/perf_event.c | 9 ++++-----
1 file changed, 4 insertions(+), 5 deletions(-)

--- git/kernel/perf_event.c~4_perf_event_init_task 2011-01-19 17:41:16.000000000 +0100
+++ git/kernel/perf_event.c 2011-01-19 18:49:23.000000000 +0100
@@ -6446,11 +6446,6 @@ int perf_event_init_context(struct task_
unsigned long flags;
int ret = 0;

- child->perf_event_ctxp[ctxn] = NULL;
-
- mutex_init(&child->perf_event_mutex);
- INIT_LIST_HEAD(&child->perf_event_list);
-
if (likely(!parent->perf_event_ctxp[ctxn]))
return 0;

@@ -6540,6 +6535,10 @@ int perf_event_init_task(struct task_str
{
int ctxn, ret;

+ memset(child->perf_event_ctxp, 0, sizeof(child->perf_event_ctxp));
+ mutex_init(&child->perf_event_mutex);
+ INIT_LIST_HEAD(&child->perf_event_list);
+
for_each_task_context_nr(ctxn) {
ret = perf_event_init_context(child, ctxn);
if (ret)


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