xfs: reset ag_max_usable when retrying failed per-ag reservation init

Commit Message

Christoph Hellwig Jan. 24, 2017, 9:07 a.m. UTC

On Mon, Jan 23, 2017 at 01:12:21PM -0800, Darrick J. Wong wrote:
> It's possible for the per-AG reservation initialization to return ENOSPC
> when fdblocks says there isn't free space.  This is a valid state for
> the reservation tracker since subsequent extent freeing activity will
> simply be captured by the reservation mechanism, but if we subsequently
> retry a failed initialization, we need to undo the changes we made to
> ag_max_usable prior to recreating the reservation.

Hmm.  I'd prefer to just not change any fields in __xfs_ag_resv_init
unless it succeeds.  So far untested and un-changelogged patch below,
I'll kick off a test run soon:

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Patch

diff --git a/fs/xfs/libxfs/xfs_ag_resv.c b/fs/xfs/libxfs/xfs_ag_resv.c
index 4773c1e..769d6e3 100644
--- a/fs/xfs/libxfs/xfs_ag_resv.c
+++ b/fs/xfs/libxfs/xfs_ag_resv.c
@@ -201,22 +201,27 @@  __xfs_ag_resv_init(
 	struct xfs_mount		*mp = pag->pag_mount;
 	struct xfs_ag_resv		*resv;
 	int				error;
+	xfs_extlen_t			reserved;
 
-	resv = xfs_perag_resv(pag, type);
 	if (used > ask)
 		ask = used;
-	resv->ar_asked = ask;
-	resv->ar_reserved = resv->ar_orig_reserved = ask - used;
-	mp->m_ag_max_usable -= ask;
-
-	trace_xfs_ag_resv_init(pag, type, ask);
+	reserved = ask - used;
 
-	error = xfs_mod_fdblocks(mp, -(int64_t)resv->ar_reserved, true);
-	if (error)
+	error = xfs_mod_fdblocks(mp, -(int64_t)reserved, true);
+	if (error) {
 		trace_xfs_ag_resv_init_error(pag->pag_mount, pag->pag_agno,
 				error, _RET_IP_);
+		return error;
+	}
 
-	return error;
+	mp->m_ag_max_usable -= ask;
+
+	resv = xfs_perag_resv(pag, type);
+	resv->ar_asked = ask;
+	resv->ar_reserved = resv->ar_orig_reserved = reserved;
+
+	trace_xfs_ag_resv_init(pag, type, ask);
+	return 0;
 }
 
 /* Create a per-AG block reservation. */