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From:   Byron Stanoszek <gandalf@winds.org>
To:     Hugh Dickins <hughd@google.com>,
        Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
Cc:     Byron Stanoszek <gandalf@winds.org>,
        Chris Down <chris@chrisdown.name>
Subject: [PATCH] tmpfs: Restore functionality of nr_inodes=0
Date:   Tue,  1 Sep 2020 23:57:15 -0400
Message-Id: <20200902035715.16414-1-gandalf@winds.org>
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Sender: linux-kernel-owner@vger.kernel.org
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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")
Cc: Chris Down <chris@chrisdown.name>
Signed-off-by: Byron Stanoszek <gandalf@winds.org>
---
 mm/shmem.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/mm/shmem.c b/mm/shmem.c
index 271548ca20f3..8e2b35ba93ad 100644
--- 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)))
-- 
2.28.0