Re: [PATCH 2/2] fs: xfs: use BUG_ON if writepage call comes from direct reclaim

From: Dave Chinner
Date: Tue Jul 03 2018 - 00:37:50 EST

On Tue, Jul 03, 2018 at 12:11:19PM +0800, Yang Shi wrote:
> direct reclaim doesn't write out filesystem page, only kswapd could do
> this. So, if it is called from direct relaim, it is definitely a bug.
> And, Mel Gorman mentioned "Ultimately, this will be a BUG_ON." in commit
> 94054fa3fca1fd78db02cb3d68d5627120f0a1d4 ("xfs: warn if direct reclaim
> tries to writeback pages"),
> It has been many years since that commit, so it should be safe to
> elevate WARN_ON to BUG_ON now.


The existing code warns and then handles the situation gracefully -
this is the appropriate way to handle incorrect calling contexts.
There is absolutely no good reason to panic production kernels
in situations like this.


Dave Chinner