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Date:   Sat, 4 Nov 2023 07:59:06 -0600
From:   Keith Busch <kbusch@kernel.org>
To:     Mikulas Patocka <mpatocka@redhat.com>
Cc:     Marek Marczykowski-G'orecki <marmarek@invisiblethingslab.com>,
        Jens Axboe <axboe@fb.com>, Christoph Hellwig <hch@lst.de>,
        Sagi Grimberg <sagi@grimberg.me>, Jan Kara <jack@suse.cz>,
        Vlastimil Babka <vbabka@suse.cz>,
        Andrew Morton <akpm@linux-foundation.org>,
        Matthew Wilcox <willy@infradead.org>,
        Michal Hocko <mhocko@suse.com>, stable@vger.kernel.org,
        regressions@lists.linux.dev, Alasdair Kergon <agk@redhat.com>,
        Mike Snitzer <snitzer@kernel.org>, dm-devel@lists.linux.dev,
        linux-mm@kvack.org
Subject: Re: Intermittent storage (dm-crypt?) freeze - regression 6.4->6.5
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On Sat, Nov 04, 2023 at 10:27:32AM +0100, Mikulas Patocka wrote:
> On Fri, 3 Nov 2023, Keith Busch wrote:
> > On Fri, Nov 03, 2023 at 09:30:07PM +0100, Marek Marczykowski-G'orecki wrote:
> > > On Fri, Nov 03, 2023 at 10:54:00AM -0600, Keith Busch wrote:
> > > > On Fri, Nov 03, 2023 at 05:15:49PM +0100, Marek Marczykowski-G'orecki wrote:
> > > > > On Thu, Nov 02, 2023 at 06:06:33PM +0100, Mikulas Patocka wrote:
> > > > > > Then, try this patch (without "iommu=panic"), reproduce the deadlock and 
> > > > > > tell us which one of the "printk" statements is triggered during the 
> > > > > > deadlock.
> > > > > 
> > > > > The "821" one - see below.
> > > > 
> > > > Thanks for confirming!
> > > > 
> > > > Could you try this patch?
> > > 
> > > Besides min3() being unhappy about types, it works.
> > 
> > Oops, should have changed the constant to "ul" instead of just "u".
> > 
> > Anyway, the overall idea makes sense to me, but I don't know the swiotlb
> > stuff well.
> > 
> > Christoph, does that patch make sense? For reference:
> > 
> >    https://lore.kernel.org/linux-mm/ZUOr-vp0yRkLyvyi@kbusch-mbp.dhcp.thefacebook.com/T/#m8d34245e0eef43f8e9fe6cba6038d77ed2a93ad6
> 
> dma_opt_mapping_size returns "min(dma_max_mapping_size(dev), size)". So 
> you don't have to call dma_max_mapping_size explicitly, you can leave the 
> file drivers/nvme/host/pci.c as it is.

Indeed.
 
> What about the other block device drivers (AHCI, SCSI...)? Should there be 
> some generic framework that restricts max_hw_sectors according to 
> dma_opt_mapping_size?

I think it's just like any other request_queue limits and the individual
drivers have to set up these.

Thinking on this again, this feels more like a max_segment_size limit
rather than a max_hw_sectors.