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    SubjectRe: ext3 lockdep warning in 2.6.25-rc6
    > I was building a kernel using "make -j 4" inside a unionfs, mounted on top
    > of ext3. The kernel is vanilla 2.6.25-rc6 plus unionfs patches. At some
    > point I forced a cache flush using "echo 3 > /proc/sys/vm/drop_caches" and I
    > got the lockdep warning below. Note that unionfs doesn't appear to be
    > involved in this lockdep warning at all, so I suspect this is probably an
    > issue between jbd and ext3 directly.
    >
    > Let me know if I can be of more help.
    Actually, I have a fix for that - attached. Can you try it? Thanks.
    Honza

    > [31270.749254] =======================================================
    > [31270.749473] [ INFO: possible circular locking dependency detected ]
    > [31270.749720] 2.6.25-rc6-unionfs2 #69
    > [31270.749831] -------------------------------------------------------
    > [31270.749958] flush-caches.sh/9702 is trying to acquire lock:
    > [31270.750171] (&journal->j_list_lock){--..}, at: [<c029ef6a>] journal_try_to_free_buffers+0xa5/0x158
    > [31270.751607]
    > [31270.751607] but task is already holding lock:
    > [31270.751607] (inode_lock){--..}, at: [<c02718bb>] drop_pagecache+0x45/0xd3
    > [31270.751607]
    > [31270.751607] which lock already depends on the new lock.
    > [31270.751607]
    > [31270.751607]
    > [31270.751607] the existing dependency chain (in reverse order) is:
    > [31270.751607]
    > [31270.751607] -> #1 (inode_lock){--..}:
    > [31270.751607] [<c0231e01>] __lock_acquire+0x934/0xab8
    > [31270.751607] [<c0232307>] lock_acquire+0x4e/0x6a
    > [31270.751607] [<c0395e33>] _spin_lock+0x23/0x32
    > [31270.751607] [<c02713d2>] __mark_inode_dirty+0xbe/0x134
    > [31270.751607] [<c0274b3a>] __set_page_dirty+0xdd/0xec
    > [31270.751607] [<c0274ba9>] mark_buffer_dirty+0x60/0x63
    > [31270.751607] [<c029d2f6>] __journal_temp_unlink_buffer+0xc9/0xce
    > [31270.751607] [<c029d43b>] __journal_unfile_buffer+0xb/0x15
    > [31270.751607] [<c029d487>] __journal_refile_buffer+0x42/0x8c
    > [31270.751607] [<c029fdd1>] journal_commit_transaction+0xc59/0xe64
    > [31270.751607] [<c02a29f1>] kjournald+0xae/0x1b0
    > [31270.751607] [<c0228833>] kthread+0x3b/0x64
    > [31270.751607] [<c02039d3>] kernel_thread_helper+0x7/0x10
    > [31270.751607] [<ffffffff>] 0xffffffff
    > [31270.751607]
    > [31270.751607] -> #0 (&journal->j_list_lock){--..}:
    > [31270.751607] [<c0231d28>] __lock_acquire+0x85b/0xab8
    > [31270.751607] [<c0232307>] lock_acquire+0x4e/0x6a
    > [31270.751607] [<c0395e33>] _spin_lock+0x23/0x32
    > [31270.751607] [<c029ef6a>] journal_try_to_free_buffers+0xa5/0x158
    > [31270.751607] [<c02925fe>] ext3_releasepage+0x53/0x5c
    > [31270.751607] [<c023e4bd>] try_to_release_page+0x32/0x3f
    > [31270.751607] [<c0243f59>] __invalidate_mapping_pages+0x69/0xc6
    > [31270.751607] [<c02718de>] drop_pagecache+0x68/0xd3
    > [31270.751607] [<c0271972>] drop_caches_sysctl_handler+0x29/0x3f
    > [31270.751607] [<c0289383>] proc_sys_write+0x61/0x7e
    > [31270.751607] [<c02594a1>] vfs_write+0x8c/0x108
    > [31270.751607] [<c0259a2b>] sys_write+0x3b/0x60
    > [31270.751607] [<c0202cee>] sysenter_past_esp+0x5f/0xa5
    > [31270.751607] [<ffffffff>] 0xffffffff
    > [31270.751607]
    > [31270.751607] other info that might help us debug this:
    > [31270.751607]
    > [31270.751607] 2 locks held by flush-caches.sh/9702:
    > [31270.751607] #0: (&type->s_umount_key#12){----}, at: [<c02718ab>] drop_pagecache+0x35/0xd3
    > [31270.751607] #1: (inode_lock){--..}, at: [<c02718bb>] drop_pagecache+0x45/0xd3
    > [31270.751608]
    > [31270.751608] stack backtrace:
    > [31270.751608] Pid: 9702, comm: flush-caches.sh Not tainted 2.6.25-rc6-unionfs2 #69
    > [31270.751608] [<c0230687>] print_circular_bug_tail+0x5b/0x66
    > [31270.751608] [<c0231d28>] __lock_acquire+0x85b/0xab8
    > [31270.751608] [<c0232307>] lock_acquire+0x4e/0x6a
    > [31270.751608] [<c029ef6a>] ? journal_try_to_free_buffers+0xa5/0x158
    > [31270.751608] [<c0395e33>] _spin_lock+0x23/0x32
    > [31270.751608] [<c029ef6a>] ? journal_try_to_free_buffers+0xa5/0x158
    > [31270.751608] [<c029ef6a>] journal_try_to_free_buffers+0xa5/0x158
    > [31270.751608] [<c02925fe>] ext3_releasepage+0x53/0x5c
    > [31270.751608] [<c023e4bd>] try_to_release_page+0x32/0x3f
    > [31270.751608] [<c0243f59>] __invalidate_mapping_pages+0x69/0xc6
    > [31270.751608] [<c02718de>] drop_pagecache+0x68/0xd3
    > [31270.751608] [<c0271972>] drop_caches_sysctl_handler+0x29/0x3f
    > [31270.751608] [<c0289383>] proc_sys_write+0x61/0x7e
    > [31270.751608] [<c0289322>] ? proc_sys_write+0x0/0x7e
    > [31270.751608] [<c02594a1>] vfs_write+0x8c/0x108
    > [31270.751608] [<c0259a2b>] sys_write+0x3b/0x60
    > [31270.751608] [<c0202cee>] sysenter_past_esp+0x5f/0xa5
    > [31270.751608] =======================
    > --
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    --
    Jan Kara <jack@suse.cz>
    SuSE CR Labs
    From f5e41087e345fa5c3b46ac36e6e4a654d2f7f624 Mon Sep 17 00:00:00 2001
    From: Jan Kara <jack@suse.cz>
    Date: Tue, 18 Mar 2008 14:38:06 +0100
    Subject: [PATCH] Fix drop_pagecache_sb() to not call __invalidate_mapping_pages() under
    inode_lock.

    Signed-off-by: Jan Kara <jack@suse.cz>
    ---
    fs/drop_caches.c | 8 +++++++-
    1 files changed, 7 insertions(+), 1 deletions(-)

    diff --git a/fs/drop_caches.c b/fs/drop_caches.c
    index 59375ef..f5aae26 100644
    --- a/fs/drop_caches.c
    +++ b/fs/drop_caches.c
    @@ -14,15 +14,21 @@ int sysctl_drop_caches;

    static void drop_pagecache_sb(struct super_block *sb)
    {
    - struct inode *inode;
    + struct inode *inode, *toput_inode = NULL;

    spin_lock(&inode_lock);
    list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {
    if (inode->i_state & (I_FREEING|I_WILL_FREE))
    continue;
    + __iget(inode);
    + spin_unlock(&inode_lock);
    __invalidate_mapping_pages(inode->i_mapping, 0, -1, true);
    + iput(toput_inode);
    + toput_inode = inode;
    + spin_lock(&inode_lock);
    }
    spin_unlock(&inode_lock);
    + iput(toput_inode);
    }

    void drop_pagecache(void)
    --
    1.5.2.4
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