[ 3.5.y.z extended stable ] Patch "GFS2: Test bufdata with buffer locked and gfs2_log_lock held" has been added to staging queue

[Herton Ronaldo Krzesinski]

This is a note to let you know that I have just added a patch titled

    GFS2: Test bufdata with buffer locked and gfs2_log_lock held

to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.5.y-queue

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.5.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Herton

------

>From 98ab5107c3429252fb5ca097dcf6c8e1109bdd90 Mon Sep 17 00:00:00 2001
From: Benjamin Marzinski <bmarzins at redhat.com>
Date: Wed, 7 Nov 2012 00:38:06 -0600
Subject: [PATCH] GFS2: Test bufdata with buffer locked and gfs2_log_lock held

commit 96e5d1d3adf56f1c7eeb07258f6a1a0a7ae9c489 upstream.

In gfs2_trans_add_bh(), gfs2 was testing if a there was a bd attached to the
buffer without having the gfs2_log_lock held. It was then assuming it would
stay attached for the rest of the function. However, without either the log
lock being held of the buffer locked, __gfs2_ail_flush() could detach bd at any
time.  This patch moves the locking before the test.  If there isn't a bd
already attached, gfs2 can safely allocate one and attach it before locking.
There is no way that the newly allocated bd could be on the ail list,
and thus no way for __gfs2_ail_flush() to detach it.

Signed-off-by: Benjamin Marzinski <bmarzins at redhat.com>
Signed-off-by: Steven Whitehouse <swhiteho at redhat.com>
Signed-off-by: Herton Ronaldo Krzesinski <herton.krzesinski at canonical.com>
---
 fs/gfs2/lops.c  |   14 ++------------
 fs/gfs2/trans.c |    8 ++++++++
 2 files changed, 10 insertions(+), 12 deletions(-)

diff --git a/fs/gfs2/lops.c b/fs/gfs2/lops.c
index 852c1be..e435b7c 100644
--- a/fs/gfs2/lops.c
+++ b/fs/gfs2/lops.c
@@ -393,12 +393,10 @@ static void buf_lo_add(struct gfs2_sbd *sdp, struct gfs2_bufdata *bd)
 	struct gfs2_meta_header *mh;
 	struct gfs2_trans *tr;

-	lock_buffer(bd->bd_bh);
-	gfs2_log_lock(sdp);
 	tr = current->journal_info;
 	tr->tr_touched = 1;
 	if (!list_empty(&bd->bd_list))
-		goto out;
+		return;
 	set_bit(GLF_LFLUSH, &bd->bd_gl->gl_flags);
 	set_bit(GLF_DIRTY, &bd->bd_gl->gl_flags);
 	gfs2_meta_check(sdp, bd->bd_bh);
@@ -409,9 +407,6 @@ static void buf_lo_add(struct gfs2_sbd *sdp, struct gfs2_bufdata *bd)
 	sdp->sd_log_num_buf++;
 	list_add(&bd->bd_list, &sdp->sd_log_le_buf);
 	tr->tr_num_buf_new++;
-out:
-	gfs2_log_unlock(sdp);
-	unlock_buffer(bd->bd_bh);
 }

 static void gfs2_check_magic(struct buffer_head *bh)
@@ -772,12 +767,10 @@ static void databuf_lo_add(struct gfs2_sbd *sdp, struct gfs2_bufdata *bd)
 	struct address_space *mapping = bd->bd_bh->b_page->mapping;
 	struct gfs2_inode *ip = GFS2_I(mapping->host);

-	lock_buffer(bd->bd_bh);
-	gfs2_log_lock(sdp);
 	if (tr)
 		tr->tr_touched = 1;
 	if (!list_empty(&bd->bd_list))
-		goto out;
+		return;
 	set_bit(GLF_LFLUSH, &bd->bd_gl->gl_flags);
 	set_bit(GLF_DIRTY, &bd->bd_gl->gl_flags);
 	if (gfs2_is_jdata(ip)) {
@@ -788,9 +781,6 @@ static void databuf_lo_add(struct gfs2_sbd *sdp, struct gfs2_bufdata *bd)
 	} else {
 		list_add_tail(&bd->bd_list, &sdp->sd_log_le_ordered);
 	}
-out:
-	gfs2_log_unlock(sdp);
-	unlock_buffer(bd->bd_bh);
 }

 /**
diff --git a/fs/gfs2/trans.c b/fs/gfs2/trans.c
index ad3e2fb..5a14e8c 100644
--- a/fs/gfs2/trans.c
+++ b/fs/gfs2/trans.c
@@ -151,14 +151,22 @@ void gfs2_trans_add_bh(struct gfs2_glock *gl, struct buffer_head *bh, int meta)
 	struct gfs2_sbd *sdp = gl->gl_sbd;
 	struct gfs2_bufdata *bd;

+	lock_buffer(bh);
+	gfs2_log_lock(sdp);
 	bd = bh->b_private;
 	if (bd)
 		gfs2_assert(sdp, bd->bd_gl == gl);
 	else {
+		gfs2_log_unlock(sdp);
+		unlock_buffer(bh);
 		gfs2_attach_bufdata(gl, bh, meta);
 		bd = bh->b_private;
+		lock_buffer(bh);
+		gfs2_log_lock(sdp);
 	}
 	lops_add(sdp, bd);
+	gfs2_log_unlock(sdp);
+	unlock_buffer(bh);
 }

 void gfs2_trans_add_revoke(struct gfs2_sbd *sdp, struct gfs2_bufdata *bd)
--
1.7.9.5