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    SubjectRe: fs: WARNING in locks_free_lock_context()
    On Wed, 3 Feb 2016 19:19:37 +0100
    William Dauchy <wdauchy@gmail.com> wrote:

    > Hello Jeff,
    >
    > On Wed, Dec 23, 2015 at 2:54 PM, Jeff Layton <jlayton@poochiereds.net> wrote:
    > > Ooh, nice catch...and just in time for Christmas.
    > >
    > > filp_close does this after the fd has been detached from the file table
    > > in __close_fd:
    > >
    > > if (likely(!(filp->f_mode & FMODE_PATH))) {
    > > dnotify_flush(filp, id);
    > > locks_remove_posix(filp, id);
    > > }
    > > fput(filp);
    > >
    > > ...and fcntl_setlk does this:
    > >
    > > /*
    > > * Attempt to detect a close/fcntl race and recover by
    > > * releasing the lock that was just acquired.
    > > */
    > > /*
    > > * we need that spin_lock here - it prevents reordering between
    > > * update of i_flctx->flc_posix and check for it done in close().
    > > * rcu_read_lock() wouldn't do.
    > > */
    > > spin_lock(&current->files->file_lock);
    > > f = fcheck(fd);
    > > spin_unlock(&current->files->file_lock);
    > > if (!error && f != filp && flock.l_type != F_UNLCK) {
    > > flock.l_type = F_UNLCK;
    > > goto again;
    > > }
    > >
    > > ...so in principle that should keep new locks from racing onto the list
    > > just after we call filp_close. Hmm...I'll see if I can reproduce and
    > > figure out how this could happen.
    >
    > Just wondering if you had the time to figure out this warning?
    >
    > Thanks,

    Yes...this commit in mainline fixes it:

    commit 7f3697e24dc3820b10f445a4a7d914fc356012d1
    Author: Jeff Layton <jeff.layton@primarydata.com>
    Date: Thu Jan 7 16:38:10 2016 -0500

    locks: fix unlock when fcntl_setlk races with a close


    ...and the patch is applicable to all kernels currently in circulation.
    The original bug is very old (from 2005).

    --
    Jeff Layton <jlayton@poochiereds.net>

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