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, 42 insertions, 16 deletions

diff --git a/fs/ext4/balloc.c b/fs/ext4/balloc.c
index 58005c01abb8..1707850301d6 100644
--- a/fs/ext4/balloc.c
+++ b/fs/ext4/balloc.c
@@ -1602,6 +1602,32 @@ out:
         return ret;
 }
 
+int ext4_claim_free_blocks(struct ext4_sb_info *sbi,
+                                                ext4_fsblk_t nblocks)
+{
+        s64 free_blocks;
+        ext4_fsblk_t root_blocks = 0;
+        struct percpu_counter *fbc = &sbi->s_freeblocks_counter;
+
+        free_blocks = percpu_counter_read(fbc);
+
+        if (!capable(CAP_SYS_RESOURCE) &&
+                sbi->s_resuid != current->fsuid &&
+                (sbi->s_resgid == 0 || !in_group_p(sbi->s_resgid)))
+                root_blocks = ext4_r_blocks_count(sbi->s_es);
+
+        if (free_blocks - (nblocks + root_blocks) < EXT4_FREEBLOCKS_WATERMARK)
+                free_blocks = percpu_counter_sum(&sbi->s_freeblocks_counter);
+
+        if (free_blocks < (root_blocks + nblocks))
+                /* we don't have free space */
+                return -ENOSPC;
+
+        /* reduce fs free blocks counter */
+        percpu_counter_sub(fbc, nblocks);
+        return 0;
+}
+
 /**
  * ext4_has_free_blocks()
  * @sbi:        in-core super block structure.
@@ -1623,18 +1649,17 @@ ext4_fsblk_t ext4_has_free_blocks(struct ext4_sb_info *sbi,
                 sbi->s_resuid != current->fsuid &&
                 (sbi->s_resgid == 0 || !in_group_p(sbi->s_resgid)))
                 root_blocks = ext4_r_blocks_count(sbi->s_es);
-#ifdef CONFIG_SMP
-        if (free_blocks - root_blocks < FBC_BATCH)
-                free_blocks =
-                        percpu_counter_sum(&sbi->s_freeblocks_counter);
-#endif
+
+        if (free_blocks - (nblocks + root_blocks) < EXT4_FREEBLOCKS_WATERMARK)
+                free_blocks = percpu_counter_sum_positive(&sbi->s_freeblocks_counter);
+
         if (free_blocks <= root_blocks)
                 /* we don't have free space */
                 return 0;
         if (free_blocks - root_blocks < nblocks)
                 return free_blocks - root_blocks;
         return nblocks;
- }
+}
 
 
 /**
@@ -1713,14 +1738,11 @@ ext4_fsblk_t ext4_old_new_blocks(handle_t *handle, struct inode *inode,
                 /*
                  * With delalloc we already reserved the blocks
                  */
-                *count = ext4_has_free_blocks(sbi, *count);
-        }
-        if (*count == 0) {
-                *errp = -ENOSPC;
-                return 0;       /*return with ENOSPC error */
+                if (ext4_claim_free_blocks(sbi, *count)) {
+                        *errp = -ENOSPC;
+                        return 0;       /*return with ENOSPC error */
+                }
         }
-        num = *count;
-
         /*
          * Check quota for allocation of this block.
          */
@@ -1915,9 +1937,13 @@ allocated:
         le16_add_cpu(&gdp->bg_free_blocks_count, -num);
         gdp->bg_checksum = ext4_group_desc_csum(sbi, group_no, gdp);
         spin_unlock(sb_bgl_lock(sbi, group_no));
-        if (!EXT4_I(inode)->i_delalloc_reserved_flag)
-                percpu_counter_sub(&sbi->s_freeblocks_counter, num);
-
+        if (!EXT4_I(inode)->i_delalloc_reserved_flag && (*count != num)) {
+                /*
+                 * we allocated less blocks than we
+                 * claimed. Add the difference back.
+                 */
+                percpu_counter_add(&sbi->s_freeblocks_counter, *count - num);
+        }
         if (sbi->s_log_groups_per_flex) {
                 ext4_group_t flex_group = ext4_flex_group(sbi, group_no);
                 spin_lock(sb_bgl_lock(sbi, flex_group));