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

[Greg Kroah-Hartman]

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

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

From: Dave Chinner <dchinner@xxxxxxxxxx>

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@xxxxxxxxxx>
Reviewed-by: Brian Foster <bfoster@xxxxxxxxxx>
Signed-off-by: Dave Chinner <david@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 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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