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exec: make de_thread() killable 

Change de_thread() to use KILLABLE rather than UNINTERRUPTIBLE while
waiting for other threads.  The only complication is that we should
clear ->group_exit_task and ->notify_count before we return, and we
should do this under tasklist_lock.  -EAGAIN is used to match the
initial signal_group_exit() check/return, it doesn't really matter.

This fixes the (unlikely) race with coredump.  de_thread() checks
signal_group_exit() before it starts to kill the subthreads, but this
can't help if another CLONE_VM (but non CLONE_THREAD) task starts the
coredumping after de_thread() unlocks ->siglock.  In this case the
killed sub-thread can block in exit_mm() waiting for coredump_finish(),
execing thread waits for that sub-thead, and the coredumping thread
waits for execing thread.  Deadlock.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Oleg Nesterov 2012-10-08 19:13:01 +02:00 committed by Linus Torvalds
parent b5356a19ce
commit d5bbd43d5f
1 changed files with 14 additions and 2 deletions
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16
fs/exec.c
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@ -878,9 +878,11 @@ static int de_thread(struct task_struct *tsk)
sig->notify_count--;
while (sig->notify_count) {
__set_current_state(TASK_UNINTERRUPTIBLE);
__set_current_state(TASK_KILLABLE);
spin_unlock_irq(lock);
schedule();
if (unlikely(__fatal_signal_pending(tsk)))
goto killed;
spin_lock_irq(lock);
}
spin_unlock_irq(lock);
@ -898,9 +900,11 @@ static int de_thread(struct task_struct *tsk)
write_lock_irq(&tasklist_lock);
if (likely(leader->exit_state))
break;
__set_current_state(TASK_UNINTERRUPTIBLE);
__set_current_state(TASK_KILLABLE);
write_unlock_irq(&tasklist_lock);
schedule();
if (unlikely(__fatal_signal_pending(tsk)))
goto killed;
}
/*
@ -994,6 +998,14 @@ static int de_thread(struct task_struct *tsk)
BUG_ON(!thread_group_leader(tsk));
return 0;
killed:
/* protects against exit_notify() and __exit_signal() */
read_lock(&tasklist_lock);
sig->group_exit_task = NULL;
sig->notify_count = 0;
read_unlock(&tasklist_lock);
return -EAGAIN;
}
char *get_task_comm(char *buf, struct task_struct *tsk)