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    SubjectRe: [PATCH] skip I_CLEAR state inodes
    On Tue, Jun 02, 2009 at 05:38:35AM +0800, Eric Sandeen wrote:
    > Wu Fengguang wrote:
    > > Add I_CLEAR tests to drop_pagecache_sb(), generic_sync_sb_inodes() and
    > > add_dquot_ref().
    > >
    > > clear_inode() will switch inode state from I_FREEING to I_CLEAR,
    > > and do so _outside_ of inode_lock. So any I_FREEING testing is
    > > incomplete without the testing of I_CLEAR.
    > >
    > > Masayoshi MIZUMA first discovered the bug in drop_pagecache_sb() and
    > > Jan Kara reminds fixing the other two cases. Thanks!
    >
    > Is there a reason it's not done for __sync_single_inode as well?

    It missed the glance because it don't have an obvious '|' in the line ;)

    > Jeff Layton asked the question and I'm following it up :)
    >
    > __sync_single_inode currently only tests I_FREEING, but I think we are
    > safe because __sync_single_inode sets I_SYNC, and clear_inode waits for
    > I_SYNC to be cleared before it changes I_STATE.

    But I_SYNC is removed just before the I_FREEING test, so we still have
    a small race window?

    > On the other hand, testing I_CLEAR here probably would be safe anyway,
    > and it'd be bonus points for consistency?

    So let's add the I_CLEAR test?

    > Same basic question for generic_sync_sb_inodes, which has a
    > BUG_ON(inode->i_state & I_FREEING), seems like this could check I_CLWAR
    > as well?

    Yes, we can add I_CLEAR here to catch more error condition.

    Thanks,
    Fengguang

    ---
    skip I_CLEAR state inodes in writeback routines

    The I_FREEING test in __sync_single_inode() is racy because
    clear_inode() can set i_state to I_CLEAR between the clear of I_SYNC
    and the test of I_FREEING.

    Also extend the coverage of BUG_ON(I_FREEING) to I_CLEAR.

    Reported-by: Jeff Layton <jlayton@redhat.com>
    Reported-by: Eric Sandeen <sandeen@sandeen.net>
    Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
    ---
    fs/fs-writeback.c | 4 ++--
    1 file changed, 2 insertions(+), 2 deletions(-)

    --- linux.orig/fs/fs-writeback.c
    +++ linux/fs/fs-writeback.c
    @@ -316,7 +316,7 @@ __sync_single_inode(struct inode *inode,
    spin_lock(&inode_lock);
    WARN_ON(inode->i_state & I_NEW);
    inode->i_state &= ~I_SYNC;
    - if (!(inode->i_state & I_FREEING)) {
    + if (!(inode->i_state & (I_FREEING | I_CLEAR))) {
    if (!(inode->i_state & I_DIRTY) &&
    mapping_tagged(mapping, PAGECACHE_TAG_DIRTY)) {
    /*
    @@ -518,7 +518,7 @@ void generic_sync_sb_inodes(struct super
    if (current_is_pdflush() && !writeback_acquire(bdi))
    break;

    - BUG_ON(inode->i_state & I_FREEING);
    + BUG_ON(inode->i_state & (I_FREEING | I_CLEAR));
    __iget(inode);
    pages_skipped = wbc->pages_skipped;
    __writeback_single_inode(inode, wbc);

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