aboutsummaryrefslogtreecommitdiff
diff options
context:
space:
mode:
authorHugh Dickins <hughd@google.com>2011-05-11 15:13:38 -0700
committerGreg Kroah-Hartman <gregkh@suse.de>2011-05-21 15:13:24 -0700
commite69ce03f62c57295465701bb86e0bca560944764 (patch)
tree27fd7cad0efec148f2e134a5d56b0d3bcac8e94f
parenta1cae297f2bfede2268dee6ce994ef3d861db9ac (diff)
downloadlinux-2.6.38-lt-ux500-e69ce03f62c57295465701bb86e0bca560944764.tar.gz
tmpfs: fix spurious ENOSPC when racing with unswap
commit 59a16ead572330deb38e5848151d30ed1af754bc upstream. Testing the shmem_swaplist replacements for igrab() revealed another bug: writes to /dev/loop0 on a tmpfs file which fills its filesystem were sometimes failing with "Buffer I/O error"s. These came from ENOSPC failures of shmem_getpage(), when racing with swapoff: the same could happen when racing with another shmem_getpage(), pulling the page in from swap in between our find_lock_page() and our taking the info->lock (though not in the single-threaded loop case). This is unacceptable, and surprising that I've not noticed it before: it dates back many years, but (presumably) was made a lot easier to reproduce in 2.6.36, which sited a page preallocation in the race window. Fix it by rechecking the page cache before settling on an ENOSPC error. Signed-off-by: Hugh Dickins <hughd@google.com> Cc: Konstantin Khlebnikov <khlebnikov@openvz.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
-rw-r--r--mm/shmem.c32
1 files changed, 22 insertions, 10 deletions
diff --git a/mm/shmem.c b/mm/shmem.c
index b44006dc002..3ca83506129 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1407,20 +1407,14 @@ repeat:
if (sbinfo->max_blocks) {
if (percpu_counter_compare(&sbinfo->used_blocks,
sbinfo->max_blocks) >= 0 ||
- shmem_acct_block(info->flags)) {
- spin_unlock(&info->lock);
- error = -ENOSPC;
- goto failed;
- }
+ shmem_acct_block(info->flags))
+ goto nospace;
percpu_counter_inc(&sbinfo->used_blocks);
spin_lock(&inode->i_lock);
inode->i_blocks += BLOCKS_PER_PAGE;
spin_unlock(&inode->i_lock);
- } else if (shmem_acct_block(info->flags)) {
- spin_unlock(&info->lock);
- error = -ENOSPC;
- goto failed;
- }
+ } else if (shmem_acct_block(info->flags))
+ goto nospace;
if (!filepage) {
int ret;
@@ -1500,6 +1494,24 @@ done:
error = 0;
goto out;
+nospace:
+ /*
+ * Perhaps the page was brought in from swap between find_lock_page
+ * and taking info->lock? We allow for that at add_to_page_cache_lru,
+ * but must also avoid reporting a spurious ENOSPC while working on a
+ * full tmpfs. (When filepage has been passed in to shmem_getpage, it
+ * is already in page cache, which prevents this race from occurring.)
+ */
+ if (!filepage) {
+ struct page *page = find_get_page(mapping, idx);
+ if (page) {
+ spin_unlock(&info->lock);
+ page_cache_release(page);
+ goto repeat;
+ }
+ }
+ spin_unlock(&info->lock);
+ error = -ENOSPC;
failed:
if (*pagep != filepage) {
unlock_page(filepage);