tmpfs: restore functionality of nr_inodes=0

Commit e809d5f0b5c9 ("tmpfs: per-superblock i_ino support") made changes
to shmem_reserve_inode() in mm/shmem.c, however the original test for
(sbinfo->max_inodes) got dropped.  This causes mounting tmpfs with option
nr_inodes=0 to fail:

  # mount -ttmpfs -onr_inodes=0 none /ext0
  mount: /ext0: mount(2) system call failed: Cannot allocate memory.

This patch restores the nr_inodes=0 functionality.

Fixes: e809d5f0b5c9 ("tmpfs: per-superblock i_ino support")
Signed-off-by: Byron Stanoszek <gandalf@winds.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Hugh Dickins <hughd@google.com>
Acked-by: Chris Down <chris@chrisdown.name>
Link: https://lkml.kernel.org/r/20200902035715.16414-1-gandalf@winds.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/shmem.c b/mm/shmem.c
index 271548c..8e2b35b 100644 (file)
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -279,11 +279,13 @@ static int shmem_reserve_inode(struct super_block *sb, ino_t *inop)
 
        if (!(sb->s_flags & SB_KERNMOUNT)) {
                spin_lock(&sbinfo->stat_lock);
-               if (!sbinfo->free_inodes) {
-                       spin_unlock(&sbinfo->stat_lock);
-                       return -ENOSPC;
+               if (sbinfo->max_inodes) {
+                       if (!sbinfo->free_inodes) {
+                               spin_unlock(&sbinfo->stat_lock);
+                               return -ENOSPC;
+                       }
+                       sbinfo->free_inodes--;
                }
-               sbinfo->free_inodes--;
                if (inop) {
                        ino = sbinfo->next_ino++;
                        if (unlikely(is_zero_ino(ino)))