path: root/kernel/posix-cpu-timers.c
diff options
authorOleg Nesterov <oleg@redhat.com>2008-11-17 15:39:47 +0100
committerIngo Molnar <mingo@elte.hu>2008-11-17 16:49:35 +0100
commitad133ba3dc283300e5b62b5b7211d2f39fbf6ee7 (patch)
tree4762492d6c564e0ac1ec47122a0d0d49b0d41e90 /kernel/posix-cpu-timers.c
parent29d7b90c15035741d15421b36000509212b3e135 (diff)
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/posix-cpu-timers.c')
1 files changed, 5 insertions, 2 deletions
diff --git a/kernel/posix-cpu-timers.c b/kernel/posix-cpu-timers.c
index 153dcb2639c..895337b16a2 100644
--- a/kernel/posix-cpu-timers.c
+++ b/kernel/posix-cpu-timers.c
@@ -1308,9 +1308,10 @@ static inline int task_cputime_expired(const struct task_cputime *sample,
static inline int fastpath_timer_check(struct task_struct *tsk)
- struct signal_struct *sig = tsk->signal;
+ struct signal_struct *sig;
- if (unlikely(!sig))
+ /* tsk == current, ensure it is safe to use ->signal/sighand */
+ if (unlikely(tsk->exit_state))
return 0;
if (!task_cputime_zero(&tsk->cputime_expires)) {
@@ -1323,6 +1324,8 @@ static inline int fastpath_timer_check(struct task_struct *tsk)
if (task_cputime_expired(&task_sample, &tsk->cputime_expires))
return 1;
+ sig = tsk->signal;
if (!task_cputime_zero(&sig->cputime_expires)) {
struct task_cputime group_sample;