commit: 05bf86b4ccfd0f197da61c67bd372111d15a6620 From: Hugh Dickins <[email protected]> Date: Sat, 14 May 2011 12:06:42 -0700 Subject: [PATCH] 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 <[email protected]> Cc: [email protected] Signed-off-by: Linus Torvalds <[email protected]> --- mm/shmem.c | 10 ++++------ 1 files changed, 4 insertions(+), 6 deletions(-) diff --git a/mm/shmem.c b/mm/shmem.c index 9e755c1..dfc7069 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) { _______________________________________________ stable mailing list [email protected] http://linux.kernel.org/mailman/listinfo/stable
