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Subject: Re: [PATCH v2 0/2] iter revert problems
To:     Al Viro <viro@zeniv.linux.org.uk>,
        Pavel Begunkov <asml.silence@gmail.com>
Cc:     io-uring@vger.kernel.org,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        Palash Oswal <oswalpalash@gmail.com>,
        Sudip Mukherjee <sudipm.mukherjee@gmail.com>,
        linux-kernel@vger.kernel.org,
        syzbot+9671693590ef5aad8953@syzkaller.appspotmail.com
References: <cover.1628780390.git.asml.silence@gmail.com>
 <3eaf5365-586d-700b-0277-e0889bfeb05d@gmail.com>
 <YSF9UFyLGZQeKbLt@zeniv-ca.linux.org.uk>
From:   Jens Axboe <axboe@kernel.dk>
Message-ID: <120e5aac-e056-1158-505b-fda41f1c99a5@kernel.dk>
Date:   Sat, 21 Aug 2021 17:13:42 -0600
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On 8/21/21 4:25 PM, Al Viro wrote:
> On Sat, Aug 21, 2021 at 03:24:28PM +0100, Pavel Begunkov wrote:
>> On 8/12/21 9:40 PM, Pavel Begunkov wrote:
>>> For the bug description see 2/2. As mentioned there the current problems
>>> is because of generic_write_checks(), but there was also a similar case
>>> fixed in 5.12, which should have been triggerable by normal
>>> write(2)/read(2) and others.
>>>
>>> It may be better to enforce reexpands as a long term solution, but for
>>> now this patchset is quickier and easier to backport.
>>
>> We need to do something with this, hopefully soon.
> 
> I still don't like that approach ;-/  If anything, I would rather do
> something like this, and to hell with one extra word on stack in
> several functions; at least that way the semantics is easy to describe.

Pavel suggested this very approach initially as well when we discussed
it, and if you're fine with the extra size_t, it is by far the best way
to get this done and not have a wonky/fragile API.

-- 
Jens Axboe