netdev - [PATCH] sctp: lock_sock_nested in sctp_sock

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Date:	Fri, 22 Jun 2007 15:14:46 -0700
From:	Zach Brown <zach.brown@...cle.com>
To:	vladislav.yasevich@...com, lksctp-developers@...ts.sourceforge.net
Cc:	netdev@...r.kernel.org, Arjan van de Ven <arjan@...ux.intel.com>
Subject: [PATCH] sctp: lock_sock_nested in sctp_sock_migrate

I'm not sure that I've gotten either the sctp or lockdep details right,
but with this patch I don't get lockdep yelling at me any more :)

------

sctp: lock_sock_nested in sctp_sock_migrate

sctp_sock_migrate() grabs the socket lock on a newly allocated socket while
holding the socket lock on an old socket.  lockdep worries that this might
be a recursive lock attempt.

 task/3026 is trying to acquire lock:
  (sk_lock-AF_INET){--..}, at: [<ffffffff88105b8c>] sctp_sock_migrate+0x2e3/0x327 [sctp]
 but task is already holding lock:
  (sk_lock-AF_INET){--..}, at: [<ffffffff8810891f>] sctp_accept+0xdf/0x1e3 [sctp]

This patch tells lockdep that this locking is safe by using
lock_sock_nested().

Signed-off-by: Zach Brown <zach.brown@...cle.com>

diff -r 8adcfdf2545b net/sctp/socket.c
--- a/net/sctp/socket.c	Fri Jun 22 11:11:33 2007 -0700
+++ b/net/sctp/socket.c	Fri Jun 22 15:05:22 2007 -0700
@@ -6084,8 +6084,11 @@ static void sctp_sock_migrate(struct soc
 	 * queued to the backlog.  This prevents a potential race between
 	 * backlog processing on the old socket and new-packet processing
 	 * on the new socket.
-	 */
-	sctp_lock_sock(newsk);
+	 *
+	 * The caller has just allocated newsk so we can guarantee that other
+	 * paths won't try to lock it and then oldsk.
+	 */
+	lock_sock_nested(newsk, SINGLE_DEPTH_NESTING);
 	sctp_assoc_migrate(assoc, newsk);
 
 	/* If the association on the newsk is already closed before accept()

-
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