From 547679087bc60277d11b11631d826895762c4505 Mon Sep 17 00:00:00 2001 From: Oleg Nesterov Date: Tue, 28 Mar 2006 16:11:30 -0800 Subject: [PATCH] [PATCH] send_sigqueue: simplify and fix the race send_sigqueue() checks PF_EXITING, then locks p->sighand->siglock. This is unsafe: 'p' can exit in between and set ->sighand = NULL. The race is theoretical, the window is tiny and irqs are disabled by the caller, so I don't think we need the fix for -stable tree. Convert send_sigqueue() to use lock_task_sighand() helper. Also, delete 'p->flags & PF_EXITING' re-check, it is unneeded and the comment is wrong. Signed-off-by: Oleg Nesterov Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/signal.c | 41 ++++------------------------------------- 1 file changed, 4 insertions(+), 37 deletions(-) diff --git a/kernel/signal.c b/kernel/signal.c index 0528a959daa..4922928d91f 100644 --- a/kernel/signal.c +++ b/kernel/signal.c @@ -1309,12 +1309,10 @@ void sigqueue_free(struct sigqueue *q) __sigqueue_free(q); } -int -send_sigqueue(int sig, struct sigqueue *q, struct task_struct *p) +int send_sigqueue(int sig, struct sigqueue *q, struct task_struct *p) { unsigned long flags; int ret = 0; - struct sighand_struct *sh; BUG_ON(!(q->flags & SIGQUEUE_PREALLOC)); @@ -1328,48 +1326,17 @@ send_sigqueue(int sig, struct sigqueue *q, struct task_struct *p) */ rcu_read_lock(); - if (unlikely(p->flags & PF_EXITING)) { + if (!likely(lock_task_sighand(p, &flags))) { ret = -1; goto out_err; } -retry: - sh = rcu_dereference(p->sighand); - - spin_lock_irqsave(&sh->siglock, flags); - if (p->sighand != sh) { - /* We raced with exec() in a multithreaded process... */ - spin_unlock_irqrestore(&sh->siglock, flags); - goto retry; - } - - /* - * We do the check here again to handle the following scenario: - * - * CPU 0 CPU 1 - * send_sigqueue - * check PF_EXITING - * interrupt exit code running - * __exit_signal - * lock sighand->siglock - * unlock sighand->siglock - * lock sh->siglock - * add(tsk->pending) flush_sigqueue(tsk->pending) - * - */ - - if (unlikely(p->flags & PF_EXITING)) { - ret = -1; - goto out; - } - if (unlikely(!list_empty(&q->list))) { /* * If an SI_TIMER entry is already queue just increment * the overrun count. */ - if (q->info.si_code != SI_TIMER) - BUG(); + BUG_ON(q->info.si_code != SI_TIMER); q->info.si_overrun++; goto out; } @@ -1385,7 +1352,7 @@ retry: signal_wake_up(p, sig == SIGKILL); out: - spin_unlock_irqrestore(&sh->siglock, flags); + unlock_task_sighand(p, &flags); out_err: rcu_read_unlock();