linux-kernel - Re: next bio iters break discard?

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Date:	Fri, 31 Jan 2014 14:58:30 -0700
From:	Jens Axboe <axboe@...nel.dk>
To:	Hugh Dickins <hughd@...gle.com>
Cc:	Kent Overstreet <kmo@...erainc.com>,
	"Martin K. Petersen" <martin.petersen@...cle.com>,
	Shaohua Li <shli@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: next bio iters break discard?

On Fri, Jan 31 2014, Hugh Dickins wrote:
> On Thu, 16 Jan 2014, Kent Overstreet wrote:
> > 
> > Ok, I reread the code and figured it out - the analagous change also has to be
> > made in __blk_segment_map_sg(). I'll mail out a patch for this tomorrow after
> > I've stared at the code more and had less beer.
> 
> I'd been hoping for a patch to try, but now your changes have hit Linus's
> tree: so today we have discard broken there too, crashing as originally
> reported on the NULL struct page pointer in __blk_recalc_rq_segments()'s
> page_to_pfn(bv.bv_page).
> 
> How to reproduce it?  I hope you'll find easier ways, but I get it with
> swapping to SSD (remember "swapon -d" to enable discard).  I'm just doing
> what I've done for years, running a pair of make -j20 kbuilds to tmpfs in
> limited RAM (I use mem=700M with 1.5G of swap: but that would be far too
> little RAM for a general config of current tree), to get plenty of fairly
> chaotic swapping but good forward progress nonetheless (if the sizes are
> too small, then it'll just thrash abysmally or be OOM-killed).
> 
> But please do send me a patch and I'll give it a try - thanks.

Hugh, sorry about that, this particular issue slipped my mind. Will get
this fixed up as soon as possible, hopefully before -rc1...

-- 
Jens Axboe

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