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Date: Tue, 22 Aug 2006 21:22:13 +0400
From: Oleg Nesterov <oleg@tv-sign.ru>
To: Andrew Morton <akpm@osdl.org>
Cc: Jens Axboe <axboe@suse.de>, linux-kernel@vger.kernel.org,
       Greg KH <greg@kroah.com>
Subject: [PATCH] elv_unregister: fix possible crash on module unload
Message-ID: <20060822172213.GA401@oleg>
References: <20060820204345.GA5750@oleg> <20060820205034.GA5755@oleg> <20060821154841.e6ea500a.akpm@osdl.org>
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An exiting task or process which didn't do I/O yet have no io context,
elv_unregister() should check it is not NULL.

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

--- 2.6.18-rc4/block/elevator.c~8_crash	2006-07-16 01:53:08.000000000 +0400
+++ 2.6.18-rc4/block/elevator.c	2006-08-22 21:13:06.000000000 +0400
@@ -765,7 +765,8 @@ void elv_unregister(struct elevator_type
 		read_lock(&tasklist_lock);
 		do_each_thread(g, p) {
 			task_lock(p);
-			e->ops.trim(p->io_context);
+			if (p->io_context)
+				e->ops.trim(p->io_context);
 			task_unlock(p);
 		} while_each_thread(g, p);
 		read_unlock(&tasklist_lock);