linux-kernel - [PATCH] tmpfs: fix off-by-one in max

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Date:	Sat, 19 Mar 2011 22:33:05 -0700 (PDT)
From:	Hugh Dickins <hughd@...gle.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	Tim Chen <tim.c.chen@...ux.intel.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: [PATCH] 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@...gle.com>
---

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

--- 2.6.38/mm/shmem.c	2011-03-14 18:20:32.000000000 -0700
+++ linux/mm/shmem.c	2011-03-19 22:02:17.000000000 -0700
@@ -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);
@@ -1399,7 +1400,8 @@ 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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