[PATCH RFC] fs: xfs: Fix xfs_trans_read_buf event tracing

[Pratyush Anand]

My root file system is xfs. As soon as I enable event for
xfs_trans_read_buf `echo xfs:xfs_trans_read_buf >>
/sys/kernel/debug/tracing/set_event`, I see a kernel panic.

A little bit of debugging shows that bp->b_fspriv is NULL many a time
when trace_xfs_trans_read_buf(bp->b_fspriv) is called.

I do not have any idea about xfs filesystem. So, I am not sure, if it
is expected to have bp->b_fspriv = NULL at this location.

This patch fixes the issue, until we have a better fix.

Signed-off-by: Pratyush Anand <panand at redhat.com>
---
 fs/xfs/xfs_trans_buf.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/xfs/xfs_trans_buf.c b/fs/xfs/xfs_trans_buf.c
index 0a4d4ab6d9a9..0b67a20643bf 100644
--- a/fs/xfs/xfs_trans_buf.c
+++ b/fs/xfs/xfs_trans_buf.c
@@ -329,7 +329,8 @@ xfs_trans_read_buf_map(
 
 	if (tp)
 		_xfs_trans_bjoin(tp, bp, 1);
-	trace_xfs_trans_read_buf(bp->b_fspriv);
+	if (bp->b_fspriv)
+		trace_xfs_trans_read_buf(bp->b_fspriv);
 	*bpp = bp;
 	return 0;
 
-- 
2.1.0