tmpfs: fix off-by-one in max_blocks checks

If you fill up a tmpfs, df was showing

  tmpfs                   460800         -         -   -  /tmp

because of an off-by-one in the max_blocks checks.  Fix it so df shows

  tmpfs                   460800    460800         0 100% /tmp

Signed-off-by: Hugh Dickins <hughd@google.com>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 4 insertions, 2 deletions

diff --git a/mm/shmem.c b/mm/shmem.c
index 58da7c150ba6..8fa27e4e582a 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -421,7 +421,8 @@ static swp_entry_t *shmem_swp_alloc(struct shmem_inode_info *info, unsigned long
                  * a waste to allocate index if we cannot allocate data.
                  */
                 if (sbinfo->max_blocks) {
-                        if (percpu_counter_compare(&sbinfo->used_blocks, (sbinfo->max_blocks - 1)) > 0)
+                        if (percpu_counter_compare(&sbinfo->used_blocks,
+                                                sbinfo->max_blocks - 1) >= 0)
                                 return ERR_PTR(-ENOSPC);
                         percpu_counter_inc(&sbinfo->used_blocks);
                         spin_lock(&inode->i_lock);
@@ -1397,7 +1398,8 @@ repeat:
                 shmem_swp_unmap(entry);
                 sbinfo = SHMEM_SB(inode->i_sb);
                 if (sbinfo->max_blocks) {
-                        if ((percpu_counter_compare(&sbinfo->used_blocks, sbinfo->max_blocks) > 0) ||
+                        if (percpu_counter_compare(&sbinfo->used_blocks,
+                                                sbinfo->max_blocks) >= 0 ||
                             shmem_acct_block(info->flags)) {
                                 spin_unlock(&info->lock);
                                 error = -ENOSPC;