linux-kernel - Re: [syzbot] [mm?] kernel BUG in sg_init

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Message-ID: <Z7ke871WFkYuwYl1@google.com>
Date: Sat, 22 Feb 2025 00:48:51 +0000
From: Yosry Ahmed <yosry.ahmed@...ux.dev>
To: Ira Weiny <ira.weiny@...el.com>
Cc: syzbot <syzbot+adbc983a1588b7805de3@...kaller.appspotmail.com>,
	Barry Song <21cnbao@...il.com>, akpm@...ux-foundation.org,
	chengming.zhou@...ux.dev, hannes@...xchg.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org, nphamcs@...il.com,
	syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [mm?] kernel BUG in sg_init_one

On Wed, Feb 12, 2025 at 09:20:24AM -0800, Yosry Ahmed wrote:
> On Mon, Mar 18, 2024 at 2:03 PM Barry Song <21cnbao@...il.com> wrote:
> >
> > On Tue, Mar 19, 2024 at 9:52 AM syzbot
> > <syzbot+adbc983a1588b7805de3@...kaller.appspotmail.com> wrote:
> > >
> > > Hello,
> > >
> > > syzbot has tested the proposed patch but the reproducer is still triggering an issue:
> > > WARNING in __kmap_to_page
> > >
> > > ------------[ cut here ]------------
> > > WARNING: CPU: 0 PID: 3529 at mm/highmem.c:167 __kmap_to_page+0x100/0x194 mm/highmem.c:167
> > > Modules linked in:
> >
> > + Ira
> >
> > Hi Ira,
> >
> > I noticed this warning is coming from commit ef6e06b2ef87077.
> >
> > you have a commit message like
> > "    Because it is intended to remove kmap_to_page() add a warn on once to
> >     the kmap checks to flag potential issues early.
> > "
> >
> > Do we have a replacement for kmap_to_page()? The background is that we
> > want to pass a highmem buffer to sg_set_page() but we only know its virt
> > address.
> 
> I am reviving this thread because new zsmalloc changes will make
> mappings sleepable, which will allow zswap to drop the memcpy() in
> zswap_decompress() -- except for the !virt_addr_valid() case. We can
> get rid of that too if we can use kmap_tp_page() in the scatterlist
> code.
> 
> Ira, could you please answer Barry's question above about
> kmap_to_page()? It has been a year and kmap_to_page() is still around.

(Trying again with Ira as the main recepient just in case)

Ira, could you please help us out here? :)

> 
> Thanks.