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Date: Fri, 8 Jan 2016 10:55:33 -0500 From: "J. Bruce Fields" <bfields@...ldses.org> To: Jeff Layton <jlayton@...chiereds.net> Cc: linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org, Dmitry Vyukov <dvyukov@...gle.com>, Alexander Viro <viro@...iv.linux.org.uk>, syzkaller <syzkaller@...glegroups.com>, Kostya Serebryany <kcc@...gle.com>, Alexander Potapenko <glider@...gle.com>, Sasha Levin <sasha.levin@...cle.com>, Eric Dumazet <edumazet@...gle.com> Subject: Re: [PATCH v2 1/6] locks: fix unlock when fcntl_setlk races with a close On Fri, Jan 08, 2016 at 08:50:09AM -0500, Jeff Layton wrote: > Dmitry reported that he was able to reproduce the WARN_ON_ONCE that > fires in locks_free_lock_context when the flc_posix list isn't empty. > > The problem turns out to be that we're basically rebuilding the > file_lock from scratch in fcntl_setlk when we discover that the setlk > has raced with a close. If the l_whence field is SEEK_CUR or SEEK_END, > then we may end up with fl_start and fl_end values that differ from > when the lock was initially set, if the file position or length of the > file has changed in the interim. > > Fix this by just reusing the same lock request structure, and simply > override fl_type value with F_UNLCK as appropriate. That ensures that > we really are unlocking the lock that was initially set. You could also just do a whole-file unlock, couldn't you? That would seem less confusing to me. But maybe I'm missing something. --b. > > While we're there, make sure that we do pop a WARN_ON_ONCE if the > removal ever fails. Also return -EBADF in this event, since that's > what we would have returned if the close had happened earlier. > > Cc: "J. Bruce Fields" <bfields@...ldses.org> > Cc: Alexander Viro <viro@...iv.linux.org.uk> > Cc: <stable@...r.kernel.org> > Fixes: c293621bbf67 (stale POSIX lock handling) > Reported-by: Dmitry Vyukov <dvyukov@...gle.com> > Signed-off-by: Jeff Layton <jeff.layton@...marydata.com> > --- > fs/locks.c | 51 ++++++++++++++++++++++++++++++--------------------- > 1 file changed, 30 insertions(+), 21 deletions(-) > > diff --git a/fs/locks.c b/fs/locks.c > index 593dca300b29..c263aff793bc 100644 > --- a/fs/locks.c > +++ b/fs/locks.c > @@ -2181,7 +2181,6 @@ int fcntl_setlk(unsigned int fd, struct file *filp, unsigned int cmd, > goto out; > } > > -again: > error = flock_to_posix_lock(filp, file_lock, &flock); > if (error) > goto out; > @@ -2223,19 +2222,22 @@ again: > * 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(¤t->files->file_lock); > - f = fcheck(fd); > - spin_unlock(¤t->files->file_lock); > - if (!error && f != filp && flock.l_type != F_UNLCK) { > - flock.l_type = F_UNLCK; > - goto again; > + if (!error && file_lock->fl_type != F_UNLCK) { > + /* > + * 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(¤t->files->file_lock); > + f = fcheck(fd); > + spin_unlock(¤t->files->file_lock); > + if (f != filp) { > + file_lock->fl_type = F_UNLCK; > + error = do_lock_file_wait(filp, cmd, file_lock); > + WARN_ON_ONCE(error); > + error = -EBADF; > + } > } > - > out: > locks_free_lock(file_lock); > return error; > @@ -2321,7 +2323,6 @@ int fcntl_setlk64(unsigned int fd, struct file *filp, unsigned int cmd, > goto out; > } > > -again: > error = flock64_to_posix_lock(filp, file_lock, &flock); > if (error) > goto out; > @@ -2363,14 +2364,22 @@ again: > * Attempt to detect a close/fcntl race and recover by > * releasing the lock that was just acquired. > */ > - spin_lock(¤t->files->file_lock); > - f = fcheck(fd); > - spin_unlock(¤t->files->file_lock); > - if (!error && f != filp && flock.l_type != F_UNLCK) { > - flock.l_type = F_UNLCK; > - goto again; > + if (!error && file_lock->fl_type != F_UNLCK) { > + /* > + * 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(¤t->files->file_lock); > + f = fcheck(fd); > + spin_unlock(¤t->files->file_lock); > + if (f != filp) { > + file_lock->fl_type = F_UNLCK; > + error = do_lock_file_wait(filp, cmd, file_lock); > + WARN_ON_ONCE(error); > + error = -EBADF; > + } > } > - > out: > locks_free_lock(file_lock); > return error; > -- > 2.5.0
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