signals: send_sig_info: don't take tasklist_lock (08d2c30c) · Commits · 戴 / test

The comment in send_sig_info() is wrong, tasklist_lock can't help. The caller must ensure the task can't go away, otherwise ->sighand can be NULL even before we take the lock. p->sighand could be changed by exec(), but I can't imagine how it is possible to prevent exit(), but not exec(). Since the things seem to work, I assume all callers are correct. However, drm_vbl_send_signals() looks broken. block_all_signals() which is solely used by drm is definitely broken. 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>

kernel/signal.c

+1 −10

Original line number	Diff line number	Diff line
		@@ -1138,8 +1138,7 @@ static int kill_something_info(int sig, struct siginfo *info, int pid)
		*/

		/*
		* These two are the most common entry points. They send a signal
		* just to the specific thread.
		* The caller must ensure the task can't exit.
		*/
		int
		send_sig_info(int sig, struct siginfo info, struct task_struct p)
		@@ -1154,17 +1153,9 @@ send_sig_info(int sig, struct siginfo info, struct task_struct p)
		if (!valid_signal(sig))
		return -EINVAL;

		/*
		* We need the tasklist lock even for the specific
		* thread case (when we don't need to follow the group
		* lists) in order to avoid races with "p->sighand"
		* going away or changing from under us.
		*/
		read_lock(&tasklist_lock);
		spin_lock_irqsave(&p->sighand->siglock, flags);
		ret = specific_send_sig_info(sig, info, p);
		spin_unlock_irqrestore(&p->sighand->siglock, flags);
		read_unlock(&tasklist_lock);
		return ret;
		}

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