[XFS] Fix block reservation mechanism.

The block reservation mechanism has been broken since the per-cpu
superblock counters were introduced. Make the block reservation code work
with the per-cpu counters by syncing the counters, snapshotting the amount
of available space and then doing a modifcation of the counter state
according to the result. Continue in a loop until we either have no space
available or we reserve some space.

SGI-PV: 956323
SGI-Modid: xfs-linux-melb:xfs-kern:27895a

Signed-off-by: David Chinner <dgc@sgi.com>
Signed-off-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Tim Shimmin <tes@sgi.com>

1 files changed, 49 insertions, 5 deletions

diff --git a/fs/xfs/xfs_fsops.c b/fs/xfs/xfs_fsops.c
index c064e72ada9e..bfde9e6d67e6 100644
--- a/fs/xfs/xfs_fsops.c
+++ b/fs/xfs/xfs_fsops.c
@@ -460,7 +460,7 @@ xfs_fs_counts(
 {
         unsigned long   s;
 
-        xfs_icsb_sync_counters_lazy(mp);
+        xfs_icsb_sync_counters_flags(mp, XFS_ICSB_LAZY_COUNT);
         s = XFS_SB_LOCK(mp);
         cnt->freedata = mp->m_sb.sb_fdblocks - XFS_ALLOC_SET_ASIDE(mp);
         cnt->freertx = mp->m_sb.sb_frextents;
@@ -491,7 +491,7 @@ xfs_reserve_blocks(
         __uint64_t              *inval,
         xfs_fsop_resblks_t      *outval)
 {
-        __int64_t               lcounter, delta;
+        __int64_t               lcounter, delta, fdblks_delta;
         __uint64_t              request;
         unsigned long           s;
 
@@ -504,17 +504,35 @@ xfs_reserve_blocks(
         }
 
         request = *inval;
+
+        /*
+         * With per-cpu counters, this becomes an interesting
+         * problem. we needto work out if we are freeing or allocation
+         * blocks first, then we can do the modification as necessary.
+         *
+         * We do this under the XFS_SB_LOCK so that if we are near
+         * ENOSPC, we will hold out any changes while we work out
+         * what to do. This means that the amount of free space can
+         * change while we do this, so we need to retry if we end up
+         * trying to reserve more space than is available.
+         *
+         * We also use the xfs_mod_incore_sb() interface so that we
+         * don't have to care about whether per cpu counter are
+         * enabled, disabled or even compiled in....
+         */
+retry:
         s = XFS_SB_LOCK(mp);
+        xfs_icsb_sync_counters_flags(mp, XFS_ICSB_SB_LOCKED);
 
         /*
          * If our previous reservation was larger than the current value,
          * then move any unused blocks back to the free pool.
          */
-
+        fdblks_delta = 0;
         if (mp->m_resblks > request) {
                 lcounter = mp->m_resblks_avail - request;
                 if (lcounter  > 0) {            /* release unused blocks */
-                        mp->m_sb.sb_fdblocks += lcounter;
+                        fdblks_delta = lcounter;
                         mp->m_resblks_avail -= lcounter;
                 }
                 mp->m_resblks = request;
@@ -522,24 +540,50 @@ xfs_reserve_blocks(
                 __int64_t       free;
 
                 free =  mp->m_sb.sb_fdblocks - XFS_ALLOC_SET_ASIDE(mp);
+                if (!free)
+                        goto out; /* ENOSPC and fdblks_delta = 0 */
+
                 delta = request - mp->m_resblks;
                 lcounter = free - delta;
                 if (lcounter < 0) {
                         /* We can't satisfy the request, just get what we can */
                         mp->m_resblks += free;
                         mp->m_resblks_avail += free;
+                        fdblks_delta = -free;
                         mp->m_sb.sb_fdblocks = XFS_ALLOC_SET_ASIDE(mp);
                 } else {
+                        fdblks_delta = -delta;
                         mp->m_sb.sb_fdblocks =
                                 lcounter + XFS_ALLOC_SET_ASIDE(mp);
                         mp->m_resblks = request;
                         mp->m_resblks_avail += delta;
                 }
         }
-
+out:
         outval->resblks = mp->m_resblks;
         outval->resblks_avail = mp->m_resblks_avail;
         XFS_SB_UNLOCK(mp, s);
+
+        if (fdblks_delta) {
+                /*
+                 * If we are putting blocks back here, m_resblks_avail is
+                 * already at it's max so this will put it in the free pool.
+                 *
+                 * If we need space, we'll either succeed in getting it
+                 * from the free block count or we'll get an enospc. If
+                 * we get a ENOSPC, it means things changed while we were
+                 * calculating fdblks_delta and so we should try again to
+                 * see if there is anything left to reserve.
+                 *
+                 * Don't set the reserved flag here - we don't want to reserve
+                 * the extra reserve blocks from the reserve.....
+                 */
+                int error;
+                error = xfs_mod_incore_sb(mp, XFS_SBS_FDBLOCKS, fdblks_delta, 0);
+                if (error == ENOSPC)
+                        goto retry;
+        }
+
         return 0;
 }