linux-kernel - [PATCH 3.19 014/175] xfs: only trace buffer items if they exist

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Message-Id: <20150304061028.727665091@linuxfoundation.org>
Date:	Tue,  3 Mar 2015 22:13:12 -0800
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Dave Chinner <dchinner@...hat.com>,
	Brian Foster <bfoster@...hat.com>,
	Dave Chinner <david@...morbit.com>
Subject: [PATCH 3.19 014/175] xfs: only trace buffer items if they exist

3.19-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Dave Chinner <dchinner@...hat.com>

commit e9892d3cc853afdda2cc69e2576d9ddb5fafad71 upstream.

The commit 2d3d0c5 ("xfs: lobotomise xfs_trans_read_buf_map()") left
a landmine in the tracing code: trace_xfs_trans_buf_read() is now
call on all buffers that are read through this interface rather than
just buffers in transactions. For buffers outside transaction
context, bp->b_fspriv is null, and so the buf log item tracing
functions cannot be called. This causes a NULL pointer dereference
in the trace_xfs_trans_buf_read() function when tracing is turned
on.

Signed-off-by: Dave Chinner <dchinner@...hat.com>
Reviewed-by: Brian Foster <bfoster@...hat.com>
Signed-off-by: Dave Chinner <david@...morbit.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 fs/xfs/xfs_trans_buf.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

--- a/fs/xfs/xfs_trans_buf.c
+++ b/fs/xfs/xfs_trans_buf.c
@@ -327,9 +327,10 @@ xfs_trans_read_buf_map(
 		return -EIO;
 	}

-	if (tp)
+	if (tp) {
 		_xfs_trans_bjoin(tp, bp, 1);
-	trace_xfs_trans_read_buf(bp->b_fspriv);
+		trace_xfs_trans_read_buf(bp->b_fspriv);
+	}
 	*bpp = bp;
 	return 0;

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