linux-kernel - Re: [PATCH] block: fix splitting segments

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Date:   Tue, 7 Jan 2020 15:06:32 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     Ming Lei <ming.lei@...hat.com>
Cc:     Jens Axboe <axboe@...nel.dk>, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, Chris Mason <clm@...com>
Subject: Re: [PATCH] block: fix splitting segments

On Wed, Jan 08, 2020 at 06:30:35AM +0800, Ming Lei wrote:
> On Tue, Jan 07, 2020 at 10:11:45AM -0800, Guenter Roeck wrote:
> > On Tue, Jan 07, 2020 at 11:23:39PM +0800, Ming Lei wrote:
> > > On Tue, Jan 07, 2020 at 04:47:08AM -0800, Guenter Roeck wrote:
> > > > Hi,
> > > > 
> > > > On Sun, Dec 29, 2019 at 10:32:30AM +0800, Ming Lei wrote:
> > > > > There are two issues in get_max_segment_size():
> > > > > 
> > > > > 1) the default segment boudary mask is bypassed, and some devices still
> > > > > require segment to not cross the default 4G boundary
> > > > > 
> > > > > 2) the segment start address isn't taken into account when checking
> > > > > segment boundary limit
> > > > > 
> > > > > Fixes the two issues.
> > > > > 
> > > > > Fixes: dcebd755926b ("block: use bio_for_each_bvec() to compute multi-page bvec count")
> > > > > Signed-off-by: Ming Lei <ming.lei@...hat.com>
> > > > 
> > > > This patch, pushed into mainline as "block: fix splitting segments on
> > > > boundary masks", results in the following crash when booting 'versatilepb'
> > > > in qemu from disk. Bisect log is attached. Detailed log is at
> > > > https://kerneltests.org/builders/qemu-arm-master/builds/1410/steps/qemubuildcommand/logs/stdio
> > > > 
> > > > Guenter
> > > > 
> > > > ---
> > > > Crash:
> > > > 
> > > > kernel BUG at block/bio.c:1885!
> > > > Internal error: Oops - BUG: 0 [#1] ARM
> > > 
> > > Please apply the following debug patch, and post the log.
> > > 
> > 
> > Here you are:
> > 
> > max_sectors 2560 max_segs 96 max_seg_size 65536 mask ffffffff
> > c738da80: 8c80/0 2416 28672, 0
> >          total sectors 56
> > 
> > (I replaced %p with %px).
> > 
> 
> Please try the following patch and see if it makes a difference.
> If not, replace trace_printk with printk in previous debug patch,
> and apply the debug patch only & post the log.
> 

The patch below fixes the problem for me.

Tested-by: Guenter Roeck <linux@...ck-us.net>

Guenter

> diff --git a/block/blk-merge.c b/block/blk-merge.c
> index 347782a24a35..f152bdee9b05 100644
> --- a/block/blk-merge.c
> +++ b/block/blk-merge.c
> @@ -159,12 +159,12 @@ static inline unsigned get_max_io_size(struct request_queue *q,
>  
>  static inline unsigned get_max_segment_size(const struct request_queue *q,
>  					    struct page *start_page,
> -					    unsigned long offset)
> +					    unsigned long long offset)
>  {
>  	unsigned long mask = queue_segment_boundary(q);
>  
>  	offset = mask & (page_to_phys(start_page) + offset);
> -	return min_t(unsigned long, mask - offset + 1,
> +	return min_t(unsigned long long, mask - offset + 1,
>  		     queue_max_segment_size(q));
>  }
>  
> 
> Thanks,
> Ming
>