From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758778Ab1ENTGy (ORCPT ); Sat, 14 May 2011 15:06:54 -0400 Received: from smtp-out.google.com ([74.125.121.67]:2853 "EHLO smtp-out.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757904Ab1ENTGt (ORCPT ); Sat, 14 May 2011 15:06:49 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=google.com; s=beta; h=date:from:x-x-sender:to:cc:subject:message-id:user-agent :mime-version:content-type; b=Gt6hCkflT/jOQJ+GrqMp4QlqVqXJoi0xKhloIMD1tfB2MmGOdTCts1R3Zxol2kl/P0 zHMjWeKWEHx3yaUXIpsw== Date: Sat, 14 May 2011 12:06:42 -0700 (PDT) From: Hugh Dickins X-X-Sender: hugh@sister.anvils To: Linus Torvalds cc: Konstantin Khlebnikov , Andrew Morton , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH] tmpfs: fix race between swapoff and writepage Message-ID: User-Agent: Alpine 2.00 (LSU 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-System-Of-Record: true Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 Cc: stable@kernel.org --- mm/shmem.c | 10 ++++------ 1 file changed, 4 insertions(+), 6 deletions(-) --- 2.6.39-rc7+/mm/shmem.c 2011-05-09 21:09:49.861399310 -0700 +++ linux/mm/shmem.c 2011-05-14 03:48:02.719548428 -0700 @@ -1037,7 +1037,6 @@ static int shmem_writepage(struct page * 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 * * 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) {