linux-kernel - [48/71] tmpfs: fix off-by-one in max

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Message-Id: <20110519180558.894710041@clark.kroah.org>
Date:	Thu, 19 May 2011 11:05:16 -0700
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Hugh Dickins <hughd@...gle.com>,
	Tim Chen <tim.c.chen@...ux.intel.com>
Subject: [48/71] tmpfs: fix off-by-one in max_blocks checks

2.6.38-stable review patch.  If anyone has any objections, please let us know.

------------------

From: Hugh Dickins <hughd@...gle.com>

commit fc5da22ae35d4720be59af8787a8a6d5e4da9517 upstream.

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@...gle.com>
Cc: Tim Chen <tim.c.chen@...ux.intel.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 mm/shmem.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -422,7 +422,8 @@ static swp_entry_t *shmem_swp_alloc(stru
 		 * 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);
@@ -1404,7 +1405,8 @@ 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;


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