ext4: Make sure all the block allocation paths reserve blocks

With delayed allocation we need to make sure block are reserved before
we attempt to allocate them. Otherwise we get block allocation failure
(ENOSPC) during writepages which cannot be handled. This would mean
silent data loss (We do a printk stating data will be lost). This patch
updates the DIO and fallocate code path to do block reservation before
block allocation. This is needed to make sure parallel DIO and fallocate
request doesn't take block out of delayed reserve space.

When free blocks count go below a threshold we switch to a slow patch
which looks at other CPU's accumulated percpu counter values.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

1 files changed, 13 insertions, 10 deletions

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 0db2ccfa0da..2c10b5058a8 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -2975,9 +2975,15 @@ ext4_mb_mark_diskspace_used(struct ext4_allocation_context *ac,
          * at write_begin() time for delayed allocation
          * do not double accounting
          */
-        if (!(ac->ac_flags & EXT4_MB_DELALLOC_RESERVED))
-                percpu_counter_sub(&sbi->s_freeblocks_counter,
-                                        ac->ac_b_ex.fe_len);
+        if (!(ac->ac_flags & EXT4_MB_DELALLOC_RESERVED) &&
+                        ac->ac_o_ex.fe_len != ac->ac_b_ex.fe_len) {
+                /*
+                 * we allocated less blocks than we calimed
+                 * Add the difference back
+                 */
+                percpu_counter_add(&sbi->s_freeblocks_counter,
+                                ac->ac_o_ex.fe_len - ac->ac_b_ex.fe_len);
+        }
 
         if (sbi->s_log_groups_per_flex) {
                 ext4_group_t flex_group = ext4_flex_group(sbi,
@@ -4389,14 +4395,11 @@ ext4_fsblk_t ext4_mb_new_blocks(handle_t *handle,
                 /*
                  * With delalloc we already reserved the blocks
                  */
-                ar->len = ext4_has_free_blocks(sbi, ar->len);
-        }
-
-        if (ar->len == 0) {
-                *errp = -ENOSPC;
-                return 0;
+                if (ext4_claim_free_blocks(sbi, ar->len)) {
+                        *errp = -ENOSPC;
+                        return 0;
+                }
         }
-
         while (ar->len && DQUOT_ALLOC_BLOCK(ar->inode, ar->len)) {
                 ar->flags |= EXT4_MB_HINT_NOPREALLOC;
                 ar->len--;