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Commit 08d2c30c authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Linus Torvalds
Browse files

signals: send_sig_info: don't take tasklist_lock 



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: default avatarOleg Nesterov <oleg@tv-sign.ru>
Cc: Roland McGrath <roland@redhat.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 3547ff3a

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;

}