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Re: [PATCH 00/19 v5] Fix filesystem freezing deadlocks

To: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Subject: Re: [PATCH 00/19 v5] Fix filesystem freezing deadlocks
From: Jan Kara <jack@xxxxxxx>
Date: Mon, 16 Apr 2012 18:16:20 +0200
Cc: dchinner@xxxxxxxxxx, LKML <linux-kernel@xxxxxxxxxxxxxxx>, linux-fsdevel@xxxxxxxxxxxxxxx, Jan Kara <jack@xxxxxxx>, Alex Elder <elder@xxxxxxxxxx>, Anton Altaparmakov <anton@xxxxxxxxxx>, Ben Myers <bpm@xxxxxxx>, Chris Mason <chris.mason@xxxxxxxxxx>, cluster-devel@xxxxxxxxxx, "David S. Miller" <davem@xxxxxxxxxxxxx>, fuse-devel@xxxxxxxxxxxxxxxxxxxxx, "J. Bruce Fields" <bfields@xxxxxxxxxxxx>, Joel Becker <jlbec@xxxxxxxxxxxx>, KONISHI Ryusuke <konishi.ryusuke@xxxxxxxxxxxxx>, linux-btrfs@xxxxxxxxxxxxxxx, linux-ext4@xxxxxxxxxxxxxxx, linux-nfs@xxxxxxxxxxxxxxx, linux-nilfs@xxxxxxxxxxxxxxx, linux-ntfs-dev@xxxxxxxxxxxxxxxxxxxxx, Mark Fasheh <mfasheh@xxxxxxxx>, Miklos Szeredi <miklos@xxxxxxxxxx>, ocfs2-devel@xxxxxxxxxxxxxx, OGAWA Hirofumi <hirofumi@xxxxxxxxxxxxxxxxxx>, Steven Whitehouse <swhiteho@xxxxxxxxxx>, "Theodore Ts'o" <tytso@xxxxxxx>, xfs@xxxxxxxxxxx
In-reply-to: <1334592845-22862-1-git-send-email-jack@xxxxxxx>
References: <1334592845-22862-1-git-send-email-jack@xxxxxxx>
User-agent: Mutt/1.5.20 (2009-06-14)
  The subject should have been [PATCH 00/27]... Sorry for the mistake.

                                                                Honza

On Mon 16-04-12 18:13:38, Jan Kara wrote:
>   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 <elder@xxxxxxxxxx>
> CC: Anton Altaparmakov <anton@xxxxxxxxxx>
> CC: Ben Myers <bpm@xxxxxxx>
> CC: Chris Mason <chris.mason@xxxxxxxxxx>
> CC: cluster-devel@xxxxxxxxxx
> CC: "David S. Miller" <davem@xxxxxxxxxxxxx>
> CC: fuse-devel@xxxxxxxxxxxxxxxxxxxxx
> CC: "J. Bruce Fields" <bfields@xxxxxxxxxxxx>
> CC: Joel Becker <jlbec@xxxxxxxxxxxx>
> CC: KONISHI Ryusuke <konishi.ryusuke@xxxxxxxxxxxxx>
> CC: linux-btrfs@xxxxxxxxxxxxxxx
> CC: linux-ext4@xxxxxxxxxxxxxxx
> CC: linux-nfs@xxxxxxxxxxxxxxx
> CC: linux-nilfs@xxxxxxxxxxxxxxx
> CC: linux-ntfs-dev@xxxxxxxxxxxxxxxxxxxxx
> CC: Mark Fasheh <mfasheh@xxxxxxxx>
> CC: Miklos Szeredi <miklos@xxxxxxxxxx>
> CC: ocfs2-devel@xxxxxxxxxxxxxx
> CC: OGAWA Hirofumi <hirofumi@xxxxxxxxxxxxxxxxxx>
> CC: Steven Whitehouse <swhiteho@xxxxxxxxxx>
> CC: "Theodore Ts'o" <tytso@xxxxxxx>
> CC: xfs@xxxxxxxxxxx
-- 
Jan Kara <jack@xxxxxxx>
SUSE Labs, CR

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