From: Jan Kara Subject: [PATCH 00/19 v5] Fix filesystem freezing deadlocks Date: Mon, 16 Apr 2012 18:13:38 +0200 Message-ID: <1334592845-22862-1-git-send-email-jack@suse.cz> Cc: dchinner@redhat.com, LKML , linux-fsdevel@vger.kernel.org, Jan Kara , Alex Elder , Anton Altaparmakov , Ben Myers , Chris Mason , cluster-devel@redhat.com, "David S. Miller" , fuse-devel@lists.sourceforge.net, "J. Bruce Fields" , Joel Becker , KONISHI Ryusuke , linux-btrfs@vger.kernel.org, linux-ext4@vger.kernel.org, linux-nfs@vger.kernel.org, linux-nilfs@vger.kernel.org, linux-ntfs-dev@lists.sourceforge.net, Mark Fasheh , Miklos Szeredi , ocfs2-devel@oss.oracle.com, OGAWA Hirofumi , Steven Whitehouse , "Theodore Ts'o" , xfs@oss.sgi.com To: Al Viro Return-path: Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org Hello, here is the fifth iteration of my patches to improve filesystem freezing. No serious changes since last time. Mostly I rebased patches and merged this series with series moving file_update_time() to ->page_mkwrite() to simplify testing and merging. Filesystem freezing is currently racy and thus we can end up with dirty data on frozen filesystem (see changelog patch 13 for detailed race description). This patch series aims at fixing this. To be able to block all places where inodes get dirtied, I've moved filesystem file_update_time() call to ->page_mkwrite callback (patches 01-07) and put freeze handling in mnt_want_write() / mnt_drop_write(). That however required some code shuffling and changes to kern_path_create() (see patches 09-12). I think the result is OK but opinions may differ ;). The advantage of this change also is that all filesystems get freeze protection almost for free - even ext2 can handle freezing well now. Another potential contention point might be patch 19. In that patch we make freeze_super() refuse to freeze the filesystem when there are open but unlinked files which may be impractical in some cases. The main reason for this is the problem with handling of file deletion from fput() called with mmap_sem held (e.g. from munmap(2)), and then there's the fact that we cannot really force such filesystem into a consistent state... But if people think that freezing with open but unlinked files should happen, then I have some possible solutions in mind (maybe as a separate patchset since this is large enough). I'm not able to hit any deadlocks, lockdep warnings, or dirty data on frozen filesystem despite beating it with fsstress and bash-shared-mapping while freezing and unfreezing for several hours (using ext4 and xfs) so I'm reasonably confident this could finally be the right solution. Changes since v4: * added a couple of Acked-by's * added some comments & doc update * added patches from series "Push file_update_time() into .page_mkwrite" since it doesn't make much sense to keep them separate anymore * rebased on top of 3.4-rc2 Changes since v3: * added third level of freezing for fs internal purposes - hooked some filesystems to use it (XFS, nilfs2) * removed racy i_size check from filemap_mkwrite() Changes since v2: * completely rewritten * freezing is now blocked at VFS entry points * two stage freezing to handle both mmapped writes and other IO The biggest changes since v1: * have two counters to provide safe state transitions for SB_FREEZE_WRITE and SB_FREEZE_TRANS states * use percpu counters instead of own percpu structure * added documentation fixes from the old fs freezing series * converted XFS to use SB_FREEZE_TRANS counter instead of its private m_active_trans counter Honza CC: Alex Elder CC: Anton Altaparmakov CC: Ben Myers CC: Chris Mason CC: cluster-devel@redhat.com CC: "David S. Miller" CC: fuse-devel@lists.sourceforge.net CC: "J. Bruce Fields" CC: Joel Becker CC: KONISHI Ryusuke CC: linux-btrfs@vger.kernel.org CC: linux-ext4@vger.kernel.org CC: linux-nfs@vger.kernel.org CC: linux-nilfs@vger.kernel.org CC: linux-ntfs-dev@lists.sourceforge.net CC: Mark Fasheh CC: Miklos Szeredi CC: ocfs2-devel@oss.oracle.com CC: OGAWA Hirofumi CC: Steven Whitehouse CC: "Theodore Ts'o" CC: xfs@oss.sgi.com