Re: [ 64/66] GFS2: Test bufdata with buffer locked andgfs2_log_lock held

[Ben Hutchings]

On Mon, 2012-11-26 at 15:13 +0000, Steven Whitehouse wrote:
> Hi,
> 
> On Sun, 2012-11-25 at 14:11 +0100, Ben Hutchings wrote:
> > On Wed, 2012-11-14 at 20:11 -0800, Greg Kroah-Hartman wrote:
> > > 3.6-stable review patch.  If anyone has any objections, please let me know.
> > > 
> > > ------------------
> > > 
> > > From: Benjamin Marzinski <bmarzins@xxxxxxxxxx>
> > > 
> > > 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@xxxxxxxxxx>
> > > Signed-off-by: Steven Whitehouse <swhiteho@xxxxxxxxxx>
> > > Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> > [...]
> > 
> > Is this needed for any earlier versions?  It looks applicable to 3.2
> > (with minor changes).
> > 
> > Ben.
> > 
> 
> Potentially yes, although I don't think we've had any reports from that
> far back,

OK, I've queued up this version for 3.2.

Ben.

---
From: Benjamin Marzinski <bmarzins@xxxxxxxxxx>
Date: Wed, 7 Nov 2012 00:38:06 -0600
Subject: 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@xxxxxxxxxx>
Signed-off-by: Steven Whitehouse <swhiteho@xxxxxxxxxx>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 fs/gfs2/lops.c  |   14 ++------------
 fs/gfs2/trans.c |    8 ++++++++
 2 files changed, 10 insertions(+), 12 deletions(-)

--- a/fs/gfs2/lops.c
+++ b/fs/gfs2/lops.c
@@ -165,16 +165,14 @@ static void buf_lo_add(struct gfs2_sbd *
 	struct gfs2_meta_header *mh;
 	struct gfs2_trans *tr;
 
-	lock_buffer(bd->bd_bh);
-	gfs2_log_lock(sdp);
 	if (!list_empty(&bd->bd_list_tr))
-		goto out;
+		return;
 	tr = current->journal_info;
 	tr->tr_touched = 1;
 	tr->tr_num_buf++;
 	list_add(&bd->bd_list_tr, &tr->tr_list_buf);
 	if (!list_empty(&le->le_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);
@@ -185,9 +183,6 @@ static void buf_lo_add(struct gfs2_sbd *
 	sdp->sd_log_num_buf++;
 	list_add(&le->le_list, &sdp->sd_log_le_buf);
 	tr->tr_num_buf_new++;
-out:
-	gfs2_log_unlock(sdp);
-	unlock_buffer(bd->bd_bh);
 }
 
 static void buf_lo_before_commit(struct gfs2_sbd *sdp)
@@ -518,11 +513,9 @@ static void databuf_lo_add(struct gfs2_s
 	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) {
 		if (!list_empty(&bd->bd_list_tr))
-			goto out;
+			return;
 		tr->tr_touched = 1;
 		if (gfs2_is_jdata(ip)) {
 			tr->tr_num_buf++;
@@ -530,7 +523,7 @@ static void databuf_lo_add(struct gfs2_s
 		}
 	}
 	if (!list_empty(&le->le_list))
-		goto out;
+		return;
 
 	set_bit(GLF_LFLUSH, &bd->bd_gl->gl_flags);
 	set_bit(GLF_DIRTY, &bd->bd_gl->gl_flags);
@@ -542,9 +535,6 @@ static void databuf_lo_add(struct gfs2_s
 	} else {
 		list_add_tail(&le->le_list, &sdp->sd_log_le_ordered);
 	}
-out:
-	gfs2_log_unlock(sdp);
-	unlock_buffer(bd->bd_bh);
 }
 
 static void gfs2_check_magic(struct buffer_head *bh)
--- a/fs/gfs2/trans.c
+++ b/fs/gfs2/trans.c
@@ -145,14 +145,22 @@ void gfs2_trans_add_bh(struct gfs2_glock
 	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->bd_le);
+	gfs2_log_unlock(sdp);
+	unlock_buffer(bh);
 }
 
 void gfs2_trans_add_revoke(struct gfs2_sbd *sdp, struct gfs2_bufdata *bd)


-- 
Ben Hutchings
It is easier to change the specification to fit the program than vice versa.

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