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author | Oleg Nesterov <oleg@tv-sign.ru> | 2006-03-28 16:11:13 -0800 |
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committer | Linus Torvalds <torvalds@g5.osdl.org> | 2006-03-28 18:36:42 -0800 |
commit | f63ee72e0fb82e504a0489490babc7612c7cd6c2 (patch) | |
tree | 85167f8016d1f746135bf1777646a58c44376af1 /kernel | |
parent | aa1757f90bea3f598b6e5d04d922a6a60200f1da (diff) | |
download | kernel_samsung_tuna-f63ee72e0fb82e504a0489490babc7612c7cd6c2.zip kernel_samsung_tuna-f63ee72e0fb82e504a0489490babc7612c7cd6c2.tar.gz kernel_samsung_tuna-f63ee72e0fb82e504a0489490babc7612c7cd6c2.tar.bz2 |
[PATCH] introduce lock_task_sighand() helper
Add lock_task_sighand() helper and converts group_send_sig_info() to use
it. Hopefully we will have more users soon.
This patch also removes '!sighand->count' and '!p->usage' checks, I think
they both are bogus, racy and unneeded (but probably it makes sense to
restore them as BUG_ON()s).
->sighand is cleared and it's ->count is decremented in release_task() with
sighand->siglock held, so it is a bug to have '!p->usage || !->count' after
we already locked and verified it is the same. On the other hand, an
already dead task without ->sighand can have a non-zero ->usage due to
ptrace, for example.
If we read the stale value of ->sighand we must see the change after
spin_lock(), because that change was done while holding that same old
->sighand.siglock.
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'kernel')
-rw-r--r-- | kernel/signal.c | 38 |
1 files changed, 24 insertions, 14 deletions
diff --git a/kernel/signal.c b/kernel/signal.c index b0b1ca9..819fa49 100644 --- a/kernel/signal.c +++ b/kernel/signal.c @@ -1120,27 +1120,37 @@ void zap_other_threads(struct task_struct *p) /* * Must be called under rcu_read_lock() or with tasklist_lock read-held. */ +struct sighand_struct *lock_task_sighand(struct task_struct *tsk, unsigned long *flags) +{ + struct sighand_struct *sighand; + + for (;;) { + sighand = rcu_dereference(tsk->sighand); + if (unlikely(sighand == NULL)) + break; + + spin_lock_irqsave(&sighand->siglock, *flags); + if (likely(sighand == tsk->sighand)) + break; + spin_unlock_irqrestore(&sighand->siglock, *flags); + } + + return sighand; +} + int group_send_sig_info(int sig, struct siginfo *info, struct task_struct *p) { unsigned long flags; - struct sighand_struct *sp; int ret; -retry: ret = check_kill_permission(sig, info, p); - if (!ret && sig && (sp = rcu_dereference(p->sighand))) { - spin_lock_irqsave(&sp->siglock, flags); - if (p->sighand != sp) { - spin_unlock_irqrestore(&sp->siglock, flags); - goto retry; - } - if ((atomic_read(&sp->count) == 0) || - (atomic_read(&p->usage) == 0)) { - spin_unlock_irqrestore(&sp->siglock, flags); - return -ESRCH; + + if (!ret && sig) { + ret = -ESRCH; + if (lock_task_sighand(p, &flags)) { + ret = __group_send_sig_info(sig, info, p); + unlock_task_sighand(p, &flags); } - ret = __group_send_sig_info(sig, info, p); - spin_unlock_irqrestore(&sp->siglock, flags); } return ret; |