linux-kernel - [PATCH] rcu: Fix wrong check in list_splice_init

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Message-Id: <1311102626-14831-1-git-send-email-schnhrr@cs.tu-berlin.de>
Date:	Tue, 19 Jul 2011 21:10:26 +0200
From:	Jan H. Schönherr <schnhrr@...tu-berlin.de>
To:	Dipankar Sarma <dipankar@...ibm.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	Corey Minyard <minyard@....org>,
	Chris Mason <chris.mason@...cle.com>,
	linux-kernel@...r.kernel.org,
	Jan H. Schönherr <schnhrr@...tu-berlin.de>
Subject: [PATCH] rcu: Fix wrong check in list_splice_init_rcu()

Hi.

If I don't miss something obvious, the following patch would
be a good idea.

There are currently two users of list_splice_init_rcu(): IPMI and btrfs.
For these, list_splice_init_rcu() is currently a NOP.

If I interpret the code correctly, this fixes a memory leak for
IPMI and something probably worse for btrfs.

The call from within btrfs was introduced only after v2.6.39 with commit
1f78160 ("Btrfs: using rcu lock in the reader side of devices list") by
converting a list_splice_init() call.

Therefore, this patch might be a candidate for v3.0.

Regards
Jan

----8<----
From: Jan H. Schönherr <schnhrr@...tu-berlin.de>

Splicing something into an empty list should work, while there is
nothing to do if the source list is empty.

Signed-off-by: Jan H. Schönherr <schnhrr@...tu-berlin.de>
---
 include/linux/rculist.h |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/include/linux/rculist.h b/include/linux/rculist.h
index e3beb31..d079290 100644
--- a/include/linux/rculist.h
+++ b/include/linux/rculist.h
@@ -183,7 +183,7 @@ static inline void list_splice_init_rcu(struct list_head *list,
 	struct list_head *last = list->prev;
 	struct list_head *at = head->next;

-	if (list_empty(head))
+	if (list_empty(list))
 		return;

 	/* "first" and "last" tracking list, so initialize it. */
-- 
1.7.6

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