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authorOleg Nesterov <oleg@redhat.com>2008-11-17 17:39:47 +0300
committerIngo Molnar <mingo@elte.hu>2008-11-17 18:49:35 +0300
commitad133ba3dc283300e5b62b5b7211d2f39fbf6ee7 (patch)
tree4762492d6c564e0ac1ec47122a0d0d49b0d41e90 /kernel/sched_stats.h
parent29d7b90c15035741d15421b36000509212b3e135 (diff)
downloadlinux-ad133ba3dc283300e5b62b5b7211d2f39fbf6ee7.tar.xz
sched, signals: fix the racy usage of ->signal in account_group_xxx/run_posix_cpu_timers
Impact: fix potential NULL dereference Contrary to ad474caca3e2a0550b7ce0706527ad5ab389a4d4 changelog, other acct_group_xxx() helpers can be called after exit_notify() by timer tick. Thanks to Roland for pointing out this. Somehow I missed this simple fact when I read the original patch, and I am afraid I confused Frank during the discussion. Sorry. Fortunately, these helpers work with current, we can check ->exit_state to ensure that ->signal can't go away under us. Also, add the comment and compiler barrier to account_group_exec_runtime(), to make sure we load ->signal only once. Signed-off-by: Oleg Nesterov <oleg@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'kernel/sched_stats.h')
-rw-r--r--kernel/sched_stats.h15
1 files changed, 11 insertions, 4 deletions
diff --git a/kernel/sched_stats.h b/kernel/sched_stats.h
index ee71bec1da66..7dbf72a2b02c 100644
--- a/kernel/sched_stats.h
+++ b/kernel/sched_stats.h
@@ -298,9 +298,11 @@ static inline void account_group_user_time(struct task_struct *tsk,
{
struct signal_struct *sig;
- sig = tsk->signal;
- if (unlikely(!sig))
+ /* tsk == current, ensure it is safe to use ->signal */
+ if (unlikely(tsk->exit_state))
return;
+
+ sig = tsk->signal;
if (sig->cputime.totals) {
struct task_cputime *times;
@@ -325,9 +327,11 @@ static inline void account_group_system_time(struct task_struct *tsk,
{
struct signal_struct *sig;
- sig = tsk->signal;
- if (unlikely(!sig))
+ /* tsk == current, ensure it is safe to use ->signal */
+ if (unlikely(tsk->exit_state))
return;
+
+ sig = tsk->signal;
if (sig->cputime.totals) {
struct task_cputime *times;
@@ -353,8 +357,11 @@ static inline void account_group_exec_runtime(struct task_struct *tsk,
struct signal_struct *sig;
sig = tsk->signal;
+ /* see __exit_signal()->task_rq_unlock_wait() */
+ barrier();
if (unlikely(!sig))
return;
+
if (sig->cputime.totals) {
struct task_cputime *times;