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

Greg Kroah-Hartman
2015-03-04T06:55:56Z

From: Dave Chinner <dchinner@redhat.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@redhat.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.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;