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    Subject[PATCH 7/9] vfs: Move waiting for inode writeback from end_writeback() to evict_inode()
    Date
    Currently, I_SYNC can never be set when evict_inode() (and thus
    end_writeback()) is called because flusher thread holds inode reference while
    inode is under writeback. As a result inode_sync_wait() in those places
    currently does nothing. However that is going to change and unveils problems
    with calling inode_sync_wait() from end_writeback(). Several filesystems call
    end_writeback() after they have deleted the inode (btrfs, gfs2, ...) and other
    filesystems (ext3, ext4, reiserfs, ...) can deadlock when waiting for I_SYNC
    because they call end_writeback() from within a transaction.

    To avoid these issues, we move inode_sync_wait() into evict_inode() before
    calling ->evict_inode(). That way we preserve the current property that
    ->evict_inode() and writeback never run in parallel and all filesystems are
    safe.

    Signed-off-by: Jan Kara <jack@suse.cz>
    ---
    fs/inode.c | 3 ++-
    1 files changed, 2 insertions(+), 1 deletions(-)

    diff --git a/fs/inode.c b/fs/inode.c
    index 9f4f5fe..501fc5d 100644
    --- a/fs/inode.c
    +++ b/fs/inode.c
    @@ -500,7 +500,6 @@ void end_writeback(struct inode *inode)
    BUG_ON(!list_empty(&inode->i_data.private_list));
    BUG_ON(!(inode->i_state & I_FREEING));
    BUG_ON(inode->i_state & I_CLEAR);
    - inode_sync_wait(inode);
    /* don't need i_lock here, no concurrent mods to i_state */
    inode->i_state = I_FREEING | I_CLEAR;
    }
    @@ -531,6 +530,8 @@ static void evict(struct inode *inode)

    inode_sb_list_del(inode);

    + inode_sync_wait(inode);
    +
    if (op->evict_inode) {
    op->evict_inode(inode);
    } else {
    --
    1.7.1


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