Re: [PATCH v2] Use atomic_t and wait_event to track dquot pincount

[Christoph Hellwig <hch@infradead.org>]

On Fri, Sep 26, 2008 at 11:32:43AM +1000, Lachlan McIlroy wrote:
>> but it doesn't fix the underlying problem that was causing the
>> spurious wakeups, which is the fact that xfs_qm_dqflush() is not
>> obeying non-blocking flush directions.
> The underlying problem has nothing to do with xfs_qm_dqflush() - the
> spurious wakeups are caused by calls to wake_up_process() that arbitrarily
> wake up a process that is in a state where it shouldn't be woken up.  If
> we don't fix the spurious wakeups then we could easily re-introduce this
> problem again.  If xfs_qm_dqflush() should be non-blocking then that's a
> separate change and it sounds like a good change too.

That sounds like there is one single underlying problem, but there
isn't.  The first problem was that we didn't re-check the condition
after sv_wait.  We must always do this, if only for robustness reasons.
The second problem we have here is that xfssyncd blocks when flushing
quotas.