diff options
| author | Hugh Dickins <hughd@google.com> | 2011-05-14 12:06:42 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2011-05-14 12:18:55 -0700 |
| commit | 05bf86b4ccfd0f197da61c67bd372111d15a6620 (patch) | |
| tree | 23db61517fad9b68b19fdbe044fa3dbe8fc2bd19 /mm/shmem.c | |
| parent | afa49791caae70cc3fd665a182eea61250795265 (diff) | |
| download | lwn-05bf86b4ccfd0f197da61c67bd372111d15a6620.tar.gz lwn-05bf86b4ccfd0f197da61c67bd372111d15a6620.zip | |
tmpfs: fix race between swapoff and writepage
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>
Cc: stable@kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/shmem.c')
| -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 9e755c166cc5..dfc7069102ee 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) { |