Hi Brian,

On Wed, Feb 03, 2021 at 09:23:59AM -0500, Brian Foster wrote:

On Tue, Jan 26, 2021 at 08:56:21PM +0800, Gao Xiang wrote:

quoted

per-AG resv failure after fixing up freespace is hard to test in an
effective way, so directly add an error injection path to observe
such error handling path works as expected.

Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Gao Xiang <redacted>
---
 fs/xfs/libxfs/xfs_ag.c       | 5 +++++
 fs/xfs/libxfs/xfs_errortag.h | 4 +++-
 fs/xfs/xfs_error.c           | 2 ++
 3 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/fs/xfs/libxfs/xfs_ag.c b/fs/xfs/libxfs/xfs_ag.c
index c6e68e265269..5076913c153f 100644
--- a/fs/xfs/libxfs/xfs_ag.c
+++ b/fs/xfs/libxfs/xfs_ag.c

@@ -23,6 +23,7 @@
 #include "xfs_ag_resv.h"
 #include "xfs_health.h"
 #include "xfs_error.h"
+#include "xfs_errortag.h"
 #include "xfs_bmap.h"
 #include "xfs_defer.h"
 #include "xfs_log_format.h"

@@ -559,6 +560,10 @@ xfs_ag_shrink_space(
 	be32_add_cpu(&agf->agf_length, -len);
 
 	err2 = xfs_ag_resv_init(agibp->b_pag, *tpp);
+
+	if (XFS_TEST_ERROR(false, mp, XFS_ERRTAG_SHRINKFS_AG_RESV_FAIL))
+		err2 = -ENOSPC;
+

Seems reasonable, but I feel like this could be broadened to serve as a
generic perag reservation error tag. I suppose we might not be able to
use it on a clean mount, but perhaps it could be reused for growfs and
remount. Hm?

I think it could be done in that way, yet currently the logic is just to
verify the shrink error handling case above rather than extend to actually
error inject per-AG reservation for now... I could rename the errortag
for later reuse (some better naming? I'm not good at this...) in advance
yet real per-AG reservation error injection might be more complicated
than just error out with -ENOSPC, and it's somewhat out of scope of this
patchset for now...

Thanks,
Gao Xiang

Brian