ocfs2: cache the mount context for dentry lock callbacks

ocfs2_drop_dentry_lock() drops the inode reference before releasing the
DENTRY lock.  This lets inode eviction release the local inode and open
locks before a remote unlink can proceed past the DENTRY lock.

A DLM callback can still arrive before the DENTRY lock has been dropped.
ocfs2_get_dentry_osb() obtains the mount context through dl_inode->i_sb,
which can access a freed inode when the downconvert thread drops the
last inode reference in its post-unlock callback:

  Downconvert thread                     DLM callback thread
  ------------------                     -------------------
  ocfs2_process_blocked_lock()
    ocfs2_dentry_post_unlock()
      ocfs2_dentry_lock_put()
        ocfs2_drop_dentry_lock()
          iput(dl->dl_inode)
          [inode reclaimed after RCU]
                                         ocfs2_blocking_ast()
                                           ocfs2_get_dentry_osb()
                                             dl->dl_inode->i_sb
          ocfs2_simple_drop_lockres()

Store the mount context in the DENTRY lock resource's l_priv field and use
the default mount-context lookup.  Recover the containing dentry lock with
container_of(), as already done for refcount locks, and remove
ocfs2_get_dentry_osb().  ocfs2_dismount_volume() shuts down the DLM before
freeing the mount context, so callbacks can use it without accessing the
inode.  Preserve the existing iput-before-unlock order to avoid delaying
local inode and open lock release until after the DENTRY lock is released.

Link: https://lore.kernel.org/pm-ocfs2-objects-candidate-0012-v9-eeb9084fb29577971229@gmail.com
Fixes: 8ed6b23709b3 ("ocfs2: revert iput deferring code in ocfs2_drop_dentry_lock")
Signed-off-by: Cen Zhang <zzzccc427@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Suggested-by: Joseph Qi <joseph.qi@linux.alibaba.com>
Reviewed-by: Joseph Qi <joseph.qi@linux.alibaba.com>
Assisted-by: LLM
Cc: Mark Fasheh <mark@fasheh.com>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: Heming Zhao <heming.zhao@suse.com>
Cc: Jia-Ju Bai <baijiaju1990@gmail.com>
Cc: <jjzuming@gmail.com>
Cc: <stable@vger.kernel.org>

0 files changed, 0 insertions, 0 deletions