diff options
| author | Oleg Nesterov <oleg@redhat.com> | 2008-11-17 15:39:47 +0100 |
|---|---|---|
| committer | Ingo Molnar <mingo@elte.hu> | 2008-11-17 16:49:35 +0100 |
| commit | ad133ba3dc283300e5b62b5b7211d2f39fbf6ee7 (patch) | |
| tree | 4762492d6c564e0ac1ec47122a0d0d49b0d41e90 | |
| parent | 29d7b90c15035741d15421b36000509212b3e135 (diff) | |
| download | linux-ad133ba3dc283300e5b62b5b7211d2f39fbf6ee7.tar.bz2 | |
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>
| -rw-r--r-- | kernel/posix-cpu-timers.c | 7 | ||||
| -rw-r--r-- | kernel/sched_stats.h | 15 |
2 files changed, 16 insertions, 6 deletions
diff --git a/kernel/posix-cpu-timers.c b/kernel/posix-cpu-timers.c index 153dcb2639c3..895337b16a24 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; 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; |