wait_task_stopped(WNOWAIT) unlocks tasklist_lock and re-checks ->exit_code and
->exit_state. This is not needed: both were valid before we dropped the lock,
and without tasklist_lock both are not stable anyway.
Read the exit_code under tasklist and report the cached value without re-check.
In fact this fixes the race with the dying child, we can report a completely
false exit_code if ->exit_state is not visible yet.
Signed-off-by: Oleg Nesterov <[email protected]>
--- 24/kernel/exit.c~2_NOREAP 2007-11-16 18:13:54.000000000 +0300
+++ 24/kernel/exit.c 2007-11-16 18:18:24.000000000 +0300
@@ -1356,10 +1356,10 @@ static int wait_task_stopped(struct task
int noreap, struct siginfo __user *infop,
int __user *stat_addr, struct rusage __user *ru)
{
- int retval, exit_code;
+ int retval, exit_code = p->exit_code;
pid_t pid;
- if (!p->exit_code)
+ if (!exit_code)
return 0;
if (delayed_group_leader && !(p->ptrace & PT_PTRACED) &&
p->signal->group_stop_count > 0)
@@ -1384,9 +1384,6 @@ static int wait_task_stopped(struct task
uid_t uid = p->uid;
int why = (p->ptrace & PT_PTRACED) ? CLD_TRAPPED : CLD_STOPPED;
- exit_code = p->exit_code;
- if (unlikely(!exit_code) || unlikely(p->exit_state))
- goto bail_ref;
return wait_noreap_copyout(p, pid, uid,
why, (exit_code << 8) | 0x7f,
infop, ru);
@@ -1417,7 +1414,6 @@ static int wait_task_stopped(struct task
* resumed, or it resumed and then died.
*/
write_unlock_irq(&tasklist_lock);
-bail_ref:
put_task_struct(p);
/*
* We are returning to the wait loop without having successfully
-
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