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    SubjectRe: [PATCH 0/4] kill-the-bkl/reiserfs: fix some lock dependency inversions
    On Tue, Sep 15, 2009 at 01:33:42AM +0400, Alexander Beregalov wrote:
    > > Hi Alexander,
    > >
    > > It should be fixed now, still in the following tree:
    > Hi!
    > Another one, similar:
    > It is v2.6.31-3123-g99bc470 plus your 805031859(kill-the-bkl/reiserfs:
    > panic in case of lock imbalance), UP.

    Although I can't reproduce it, I think I see how that can happen.

    On mount time, we have the following dependency:

    reiserfs_lock -> bdev_mutex -> sysfs_mutex

    which happens while calling journal_init_dev() because
    we open the device there.

    But also in case of mmap on a reiserfs filesystem we
    may call reiserfs_readpages(), holding the reiserfs lock
    while already holding mm->mmap_sem

    The above dependency is then updated:

    ------- reiserfs_lock -> bdev_mutex -> sysfs_mutex

    And later, while doing a readdir() on a sysfs directory,
    sysfs calls filldir, which might_fault, and then might grab
    mmap_sem. filldir is called there while holding sys_mutex,
    creating the new following dependency

    sysfs_mutex -> mmap_sem

    Hence the inversion.
    It seems the deadlock can't ever happen, I even don't see
    corner cases where it could happen.

    But still, this dependency should disappear.

    Could you please tell me if the following patch makes it shut down?

    Otherwise, I may need your config. I don't know why, but I suspect
    the lock_acquire(mmap_sem) in might_fault doesn't trigger needed the lockdep
    check, although I have the appropriate debug config, at least it seems.
    But anyway, it should also happen in my box but it doesn't...


    The patch:

    diff --git a/fs/reiserfs/journal.c b/fs/reiserfs/journal.c
    index d23d6d7..59f7a4c 100644
    --- a/fs/reiserfs/journal.c
    +++ b/fs/reiserfs/journal.c
    @@ -2801,11 +2801,14 @@ int journal_init(struct super_block *sb, const char *j_dev_name,
    goto free_and_return;

    + reiserfs_write_unlock(sb);
    if (journal_init_dev(sb, journal, j_dev_name) != 0) {
    reiserfs_warning(sb, "sh-462",
    "unable to initialize jornal device");
    + reiserfs_write_lock(sb);
    goto free_and_return;
    + reiserfs_write_lock(sb);

    rs = SB_DISK_SUPER_BLOCK(sb);

     \ /
      Last update: 2009-09-16 22:41    [W:0.024 / U:0.232 seconds]
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