[tip:perf/urgent] perf: Fix perf_event_init_task()/perf_event_free_task() interaction

[tip-bot for Oleg Nesterov]

Commit-ID:  8550d7cb6ed6c89add49c3b6ad4c753ab8a3d7f9
Gitweb:     http://git.kernel.org/tip/8550d7cb6ed6c89add49c3b6ad4c753ab8a3d7f9
Author:     Oleg Nesterov <oleg@xxxxxxxxxx>
AuthorDate: Wed, 19 Jan 2011 19:22:28 +0100
Committer:  Ingo Molnar <mingo@xxxxxxx>
CommitDate: Wed, 19 Jan 2011 20:04:28 +0100

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@xxxxxxxxxx>
Acked-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Cc: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Cc: Frederic Weisbecker <fweisbec@xxxxxxxxx>
Cc: Paul Mackerras <paulus@xxxxxxxxx>
Cc: Prasad <prasad@xxxxxxxxxxxxxxxxxx>
Cc: Roland McGrath <roland@xxxxxxxxxx>
LKML-Reference: <20110119182228.GC12183@xxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxx>
---
 kernel/perf_event.c |    9 ++++-----
 1 files changed, 4 insertions(+), 5 deletions(-)

diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index 4ec55ef..244ca3a 100644
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -6446,11 +6446,6 @@ int perf_event_init_context(struct task_struct *child, int ctxn)
 	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;
 
@@ -6539,6 +6534,10 @@ int perf_event_init_task(struct task_struct *child)
 {
 	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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