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>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Prasad <prasad@linux.vnet.ibm.com>
Cc: Roland McGrath <roland@redhat.com>
LKML-Reference: <20110119182228.GC12183@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 4 insertions, 5 deletions

diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index 4ec55ef5810c..244ca3acb0ee 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)