Re: [PATCH] ocfs2: fix circular locking dependency in ocfs2_acquire_dquot

[Szymon Wilczek]

Hi Joseph,

You are absolutely correct. Since ocfs2_disable_quotas() completes before
ocfs2_shutdown_local_alloc(), these two specific paths likely cannot race
at runtime.

However, the Lockdep report is based on lock classes, not just runtime
concurrency.

1. The shutdown path (ocfs2_shutdown_local_alloc) teaches Lockdep:
   sb_internal -> ocfs2_sysfile_lock_key (on Local Alloc inode)

2. The acquire path (ocfs2_acquire_dquot) teaches Lockdep:
   ocfs2_sysfile_lock_key (on Quota inode) -> sb_internal

Because both inodes use the same lock class (ocfs2_sysfile_lock_key),
Lockdep sees a contradiction:
   sb_internal -> sysfile -> sb_internal

Even if they don't race, this inconsistent ordering is a violation
that Lockdep flags. Fixing the order in acquire_dquot resolves this
contradiction and ensures sb_internal (freeze protection) is always
taken outermost.

Thanks,
Szymon