Re: [RFC][PATCH 04/16] writeback: fix possible race when shuttingdown bdi

[Christoph Hellwig]

On Fri, Jul 16, 2010 at 03:45:00PM +0300, Artem Bityutskiy wrote:
> From: Artem Bityutskiy <Artem.Bityutskiy@xxxxxxxxx>
> 
> Current bdi code has the following race between 'bdi_wb_shutdown()'
> and 'bdi_forker_thread()'.
> 
> Initial condition: BDI_pending is cleaned, bdi has no writeback thread,
> because it was inactive and exited, 'bdi_wb_shutdown()' and
> 'bdi_forker_thread()' are executed concurrently.

Wouldn't it be better to have a per-bdi mutex to serialize thread
creation and shutdown?  And please also kill the bit wait in favour
of a proper wait queue - the bit wait interface really is just a hack
for structures that are very size sensitive, which the backing device
is not.

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