linux-kernel - [PATCH] signals-do_tkill-dont-use-tasklist

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Date:	Fri, 7 Mar 2008 14:05:12 +0300
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Ingo Molnar <mingo@...e.hu>,
	Roland McGrath <roland@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH] signals-do_tkill-dont-use-tasklist_lock-comment

On 03/07, Christoph Hellwig wrote:
>
> On Fri, Mar 07, 2008 at 12:58:13PM +0300, Oleg Nesterov wrote:
> > Note that we don't return an error if lock_task_sighand() fails, we pretend the
> > task dies after receiving the signal. Otherwise, we should fight with the nasty
> > races with mt-exec without having any advantage.
> 
> This should be mentioned in a comment in the code.

Signed-off-by: Oleg Nesterov <oleg@...sign.ru>

--- 25/kernel/signal.c~2__COMMENT	2008-03-07 13:06:17.000000000 +0300
+++ 25/kernel/signal.c	2008-03-07 13:59:09.000000000 +0300
@@ -2201,6 +2201,10 @@ static int do_tkill(int tgid, int pid, i
 		/*
 		 * The null signal is a permissions and process existence
 		 * probe.  No signal is actually delivered.
+		 *
+		 * If lock_task_sighand() fails we pretend the task dies
+		 * after receiving the signal. The window is tiny, and the
+		 * signal is private anyway.
 		 */
 		if (!error && sig && lock_task_sighand(p, &flags)) {
 			error = specific_send_sig_info(sig, &info, p);

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