linux-kernel - Re: reeze while write on external usb 3.0 hard disk [Bug 204095]

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Message-ID: <20190930182501.GA4043@lazy.lzy>
Date:   Mon, 30 Sep 2019 20:25:01 +0200
From:   Piergiorgio Sartor <piergiorgio.sartor@...go.de>
To:     Alan Stern <stern@...land.harvard.edu>
Cc:     Piergiorgio Sartor <piergiorgio.sartor@...go.de>,
        Christoph Hellwig <hch@....de>, Jens Axboe <axboe@...nel.dk>,
        USB list <linux-usb@...r.kernel.org>,
        linux-block@...r.kernel.org,
        Kernel development list <linux-kernel@...r.kernel.org>
Subject: Re: reeze while write on external usb 3.0 hard disk [Bug 204095]

On Sun, Sep 29, 2019 at 09:01:48PM -0400, Alan Stern wrote:
> On Sun, 29 Sep 2019, Piergiorgio Sartor wrote:
> 
> > On Wed, Sep 25, 2019 at 02:31:58PM -0400, Alan Stern wrote:
> > > On Wed, 25 Sep 2019, Piergiorgio Sartor wrote:
> > > 
> > > > On Mon, Aug 26, 2019 at 07:38:33PM +0200, Piergiorgio Sartor wrote:
> > > > > On Tue, Aug 20, 2019 at 06:37:22PM +0200, Piergiorgio Sartor wrote:
> > > > > > On Tue, Aug 20, 2019 at 09:23:26AM +0200, Christoph Hellwig wrote:
> > > > > > > On Mon, Aug 19, 2019 at 10:14:25AM -0400, Alan Stern wrote:
> > > > > > > > Let's bring this to the attention of some more people.
> > > > > > > > 
> > > > > > > > It looks like the bug that was supposed to be fixed by commit
> > > > > > > > d74ffae8b8dd ("usb-storage: Add a limitation for
> > > > > > > > blk_queue_max_hw_sectors()"), which is part of 5.2.5, but apparently
> > > > > > > > the bug still occurs.
> > > > > > > 
> > > > > > > Piergiorgio,
> > > > > > > 
> > > > > > > can you dump the content of max_hw_sectors_kb file for your USB storage
> > > > > > > device and send that to this thread?
> > > > > > 
> > > > > > Hi all,
> > > > > > 
> > > > > > for both kernels, 5.1.20 (working) and 5.2.8 (not working),
> > > > > > the content of /sys/dev/x:y/queue/max_hw_sectors_kb is 512
> > > > > > for USB storage devices (2.0 and 3.0).
> > > > > > 
> > > > > > This is for the PC showing the issue.
> > > > > > 
> > > > > > In an other PC, which does not show the issus at the moment,
> > > > > > the values are 120, for USB2.0, and 256, for USB3.0.
> 
> > > One thing you can try is git bisect from 5.1.20 (or maybe just 5.1.0)  
> > > to 5.2.8.  If you can identify a particular commit which caused the
> > > problem to start, that would help.
> > 
> > OK, I tried a bisect (2 days compilations...).
> > Assuming I've done everything correctly (how to
> > test this? How to remove the guilty patch?), this
> > was the result:
> > 
> > 09324d32d2a0843e66652a087da6f77924358e62 is the first bad commit
> > commit 09324d32d2a0843e66652a087da6f77924358e62
> > Author: Christoph Hellwig <hch@....de>
> > Date:   Tue May 21 09:01:41 2019 +0200
> > 
> >     block: force an unlimited segment size on queues with a virt boundary
> > 
> >     We currently fail to update the front/back segment size in the bio when
> >     deciding to allow an otherwise gappy segement to a device with a
> >     virt boundary.  The reason why this did not cause problems is that
> >     devices with a virt boundary fundamentally don't use segments as we
> >     know it and thus don't care.  Make that assumption formal by forcing
> >     an unlimited segement size in this case.
> > 
> >     Fixes: f6970f83ef79 ("block: don't check if adjacent bvecs in one bio can be mergeable")
> >     Signed-off-by: Christoph Hellwig <hch@....de>
> >     Reviewed-by: Ming Lei <ming.lei@...hat.com>
> >     Reviewed-by: Hannes Reinecke <hare@...e.com>
> >     Signed-off-by: Jens Axboe <axboe@...nel.dk>
> > 
> > :040000 040000 57ba04a02f948022c0f6ba24bfa36f3b565b2440 8c925f71ce75042529c001bf244b30565d19ebf3 M      block
> > 
> > What to do now?
> 
> Here's how to verify that the bisection got a correct result.  First, 
> do a git checkout of commit 09324d32d2a0, build the kernel, and make 
> sure that it exhibits the problem.
> 
> Next, have git write out the contents of that commit in the form of a
> patch (git show commit-id >patchfile), and revert it (git apply -R
> patchfile).  Build the kernel from that tree, and make sure that it
> does not exhibit the problem.  If it doesn't, you have definitely shown
> that this commit is the cause (or at least, is _one_ of the causes).

I tried as suggested, i.e. jumping to commit
09324d32d2a0843e66652a087da6f77924358e62, testing,
removing the patch, testing.
The result was as expected.
I was able to reproduce the issue with the commit,
I was not able to reproduce it without.
It seems this patch / commit is causing the problem.
Directly or indirectly.

What are the next steps?

Thanks!

bye,

-- 

piergiorgio