sched: run_posix_cpu_timers: Don't check ->exit_state, use lock_task_sighand()

run_posix_cpu_timers() doesn't work if current has already passed
exit_notify(). This was needed to prevent the races with do_wait().

Since ea6d290c ->signal is always valid and can't go away. We can
remove the "tsk->exit_state == 0" in fastpath_timer_check() and
convert run_posix_cpu_timers() to use lock_task_sighand().

Note: it makes sense to take group_leader's sighand instead, the
sub-thread still uses CPU after release_task(). But we need more
changes to do this.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <20100610231018.GA25942@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 4 insertions, 6 deletions

diff --git a/kernel/posix-cpu-timers.c b/kernel/posix-cpu-timers.c
index bf2a6502860a..d5dbef5e89e6 100644
--- a/kernel/posix-cpu-timers.c
+++ b/kernel/posix-cpu-timers.c
@@ -1272,10 +1272,6 @@ static inline int fastpath_timer_check(struct task_struct *tsk)
 {
         struct signal_struct *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)) {
                 struct task_cputime task_sample = {
                         .utime = tsk->utime,
@@ -1308,6 +1304,7 @@ void run_posix_cpu_timers(struct task_struct *tsk)
 {
         LIST_HEAD(firing);
         struct k_itimer *timer, *next;
+        unsigned long flags;
 
         BUG_ON(!irqs_disabled());
 
@@ -1318,7 +1315,8 @@ void run_posix_cpu_timers(struct task_struct *tsk)
         if (!fastpath_timer_check(tsk))
                 return;
 
-        spin_lock(&tsk->sighand->siglock);
+        if (!lock_task_sighand(tsk, &flags))
+                return;
         /*
          * Here we take off tsk->signal->cpu_timers[N] and
          * tsk->cpu_timers[N] all the timers that are firing, and
@@ -1340,7 +1338,7 @@ void run_posix_cpu_timers(struct task_struct *tsk)
          * that gets the timer lock before we do will give it up and
          * spin until we've taken care of that timer below.
          */
-        spin_unlock(&tsk->sighand->siglock);
+        unlock_task_sighand(tsk, &flags);
 
         /*
          * Now that all the timers on our list have the firing flag,