Re: [PATCH] workqueue: relax lockdep annotation on flush_work()

[Peter Zijlstra <peterz@infradead.org>]

On Wed, 2010-12-29 at 13:57 +0100, Tejun Heo wrote:
> Currently, the lockdep annotation in flush_work() requires exclusive
> access on the workqueue the target work is queued on and triggers
> warning if a work is trying to flush another work on the same
> workqueue; however, this is no longer true as workqueues can now
> execute multiple works concurrently.
> 
> This patch adds lock_map_acquire_read() and make process_one_work()
> hold read access to the workqueue while executing a work and
> start_flush_work() check for write access if concurrnecy level is one
> and read access if higher.
> 
> This better represents what's going on and removes spurious lockdep
> warnings which are triggered by fake dependency chain created through
> flush_work().

Is this still true in the low memory situation where we're running the
emergency thread? I can imagine the emergency thread trying to flush
itself isn't really a good thing.