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authorOleg Nesterov <oleg@tv-sign.ru>2007-10-16 23:27:23 -0700
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2007-10-17 08:42:54 -0700
commit6db840fa7887980ef68a649640d506fe069eef0c (patch)
tree6248c1e65b572f1c2b14c46848e5a18df003f60e
parent356d6d5058c8082b9e811838ab2fa27825c947e4 (diff)
exec: RT sub-thread can livelock and monopolize CPU on exec
de_thread() yields waiting for ->group_leader to be a zombie. This deadlocks if an rt-prio execer shares the same cpu with ->group_leader. Change the code to use ->group_exit_task/notify_count mechanics. This patch certainly uglifies the code, perhaps someone can suggest something better. Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru> Cc: Roland McGrath <roland@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--fs/exec.c28
-rw-r--r--kernel/exit.c10
2 files changed, 22 insertions, 16 deletions
diff --git a/fs/exec.c b/fs/exec.c
index ab5a4a3ece46..aa470a93540a 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -801,16 +801,15 @@ static int de_thread(struct task_struct *tsk)
hrtimer_restart(&sig->real_timer);
spin_lock_irq(lock);
}
+
+ sig->notify_count = count;
+ sig->group_exit_task = tsk;
while (atomic_read(&sig->count) > count) {
- sig->group_exit_task = tsk;
- sig->notify_count = count;
__set_current_state(TASK_UNINTERRUPTIBLE);
spin_unlock_irq(lock);
schedule();
spin_lock_irq(lock);
}
- sig->group_exit_task = NULL;
- sig->notify_count = 0;
spin_unlock_irq(lock);
/*
@@ -819,14 +818,17 @@ static int de_thread(struct task_struct *tsk)
* and to assume its PID:
*/
if (!thread_group_leader(tsk)) {
- /*
- * Wait for the thread group leader to be a zombie.
- * It should already be zombie at this point, most
- * of the time.
- */
leader = tsk->group_leader;
- while (leader->exit_state != EXIT_ZOMBIE)
- yield();
+
+ sig->notify_count = -1;
+ for (;;) {
+ write_lock_irq(&tasklist_lock);
+ if (likely(leader->exit_state))
+ break;
+ __set_current_state(TASK_UNINTERRUPTIBLE);
+ write_unlock_irq(&tasklist_lock);
+ schedule();
+ }
/*
* The only record we have of the real-time age of a
@@ -840,8 +842,6 @@ static int de_thread(struct task_struct *tsk)
*/
tsk->start_time = leader->start_time;
- write_lock_irq(&tasklist_lock);
-
BUG_ON(leader->tgid != tsk->tgid);
BUG_ON(tsk->pid == tsk->tgid);
/*
@@ -874,6 +874,8 @@ static int de_thread(struct task_struct *tsk)
write_unlock_irq(&tasklist_lock);
}
+ sig->group_exit_task = NULL;
+ sig->notify_count = 0;
/*
* There may be one thread left which is just exiting,
* but it's safe to stop telling the group to kill themselves.
diff --git a/kernel/exit.c b/kernel/exit.c
index 25f6805be5fe..4c108df88a37 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -92,10 +92,9 @@ static void __exit_signal(struct task_struct *tsk)
* If there is any task waiting for the group exit
* then notify it:
*/
- if (sig->group_exit_task && atomic_read(&sig->count) == sig->notify_count) {
+ if (sig->group_exit_task && atomic_read(&sig->count) == sig->notify_count)
wake_up_process(sig->group_exit_task);
- sig->group_exit_task = NULL;
- }
+
if (tsk == sig->curr_target)
sig->curr_target = next_thread(tsk);
/*
@@ -827,6 +826,11 @@ static void exit_notify(struct task_struct *tsk)
state = EXIT_DEAD;
tsk->exit_state = state;
+ if (thread_group_leader(tsk) &&
+ tsk->signal->notify_count < 0 &&
+ tsk->signal->group_exit_task)
+ wake_up_process(tsk->signal->group_exit_task);
+
write_unlock_irq(&tasklist_lock);
list_for_each_safe(_p, _n, &ptrace_dead) {