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signals: send_sig_info: don't take tasklist_lock

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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>
This commit is contained in:
Oleg Nesterov
2008-04-30 00:52:51 -07:00
committed by Linus Torvalds
parent 3547ff3aef
commit 08d2c30ce9
1 changed files with 1 additions and 10 deletions
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11
kernel/signal.c
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@@ -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 * The caller must ensure the task can't exit.
* just to the specific thread.
*/ */
int int
send_sig_info(int sig, struct siginfo *info, struct task_struct *p) 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)) if (!valid_signal(sig))
return -EINVAL; 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); spin_lock_irqsave(&p->sighand->siglock, flags);
ret = specific_send_sig_info(sig, info, p); ret = specific_send_sig_info(sig, info, p);
spin_unlock_irqrestore(&p->sighand->siglock, flags); spin_unlock_irqrestore(&p->sighand->siglock, flags);
read_unlock(&tasklist_lock);
return ret; return ret;
} }