diff options
| author | Hugh Dickins <hughd@google.com> | 2011-05-14 12:06:42 -0700 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@suse.de> | 2011-05-21 15:13:23 -0700 |
| commit | 3c249016aed25db602d4849c2690521cf5e1ff2f (patch) | |
| tree | fab2efbc5acbba49a2d744ea722fd0795f0a98c8 | |
| parent | a621088213d3272950a85875afc25cc87b01b560 (diff) | |
tmpfs: fix race between swapoff and writepage
commit 05bf86b4ccfd0f197da61c67bd372111d15a6620 upstream.
Shame on me! Commit b1dea800ac39 "tmpfs: fix race between umount and
writepage" fixed the advertized race, but introduced another: as even
its comment makes clear, we cannot safely rely on a peek at list_empty()
while holding no lock - until info->swapped is set, shmem_unuse_inode()
may delete any formerly-swapped inode from the shmem_swaplist, which
in this case would leave a swap area impossible to swapoff.
Although I don't relish taking the mutex every time, I don't care much
for the alternatives either; and at least the peek at list_empty() in
shmem_evict_inode() (a hotter path since most inodes would never have
been swapped) remains safe, because we already truncated the whole file.
Signed-off-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
| -rw-r--r-- | mm/shmem.c | 10 |
1 files changed, 4 insertions, 6 deletions
diff --git a/mm/shmem.c b/mm/shmem.c index bd376ba6fd3..436fef08356 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -1037,7 +1037,6 @@ static int shmem_writepage(struct page *page, struct writeback_control *wbc) struct address_space *mapping; unsigned long index; struct inode *inode; - bool unlock_mutex = false; BUG_ON(!PageLocked(page)); mapping = page->mapping; @@ -1072,15 +1071,14 @@ static int shmem_writepage(struct page *page, struct writeback_control *wbc) * we've taken the spinlock, because shmem_unuse_inode() will * prune a !swapped inode from the swaplist under both locks. */ - if (swap.val && list_empty(&info->swaplist)) { + if (swap.val) { mutex_lock(&shmem_swaplist_mutex); - /* move instead of add in case we're racing */ - list_move_tail(&info->swaplist, &shmem_swaplist); - unlock_mutex = true; + if (list_empty(&info->swaplist)) + list_add_tail(&info->swaplist, &shmem_swaplist); } spin_lock(&info->lock); - if (unlock_mutex) + if (swap.val) mutex_unlock(&shmem_swaplist_mutex); if (index >= info->next_index) { |