Re: [PATCH 1/2] bdi: mark the bdi flusher busy when being forked

[Christoph Hellwig <hch@xxxxxxxxxxxxx>]

On Thu, Apr 07, 2011 at 04:19:55PM +1000, Dave Chinner wrote:
> From: Dave Chinner <dchinner@xxxxxxxxxx>
> 
> Recetn attempts to use writeback_inode_sb_nr_if_idle() in XFs from
> memory reclaim context have caused deadlocks because memory reclaim
> call be called from a failed allocation during forking a flusher
> thread. The shrinker then attempts to trigger writeback and the bdi
> is considered idle because writeback is not in progress yet and then
> deadlocks because bdi_queue_work() blocks waiting for the
> BDI_Pending bit to clear which will never happen because it needs
> the fork to complete.
> 
> To avoid this deadlock, consider writeback to be in progress if the
> flusher thread is being created. This prevents reclaim from blocking
> waiting for it be forked and hence avoids the deadlock.

Looks good,

Reviewed-by: Christoph Hellwig <hch@xxxxxx>