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Mon, 4 Mar 2024 20:15:05 +0800 Message-ID: <5c883e3c-e96c-c6ba-7797-dc48de4698ca@huawei.com> Date: Mon, 4 Mar 2024 20:15:04 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101 Thunderbird/91.8.0 Subject: Re: [bug report] dead loop in generic_perform_write() //Re: [PATCH v7 07/12] iov_iter: Convert iterate*() to inline funcs To: David Howells , Linus Torvalds CC: Al Viro , Jens Axboe , Christoph Hellwig , Christian Brauner , David Laight , Matthew Wilcox , Jeff Layton , , , , , , Kefeng Wang References: <20230925120309.1731676-1-dhowells@redhat.com> <20230925120309.1731676-8-dhowells@redhat.com> <4e80924d-9c85-f13a-722a-6a5d2b1c225a@huawei.com> <769021.1709553367@warthog.procyon.org.uk> From: Tong Tiangen In-Reply-To: <769021.1709553367@warthog.procyon.org.uk> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit X-Originating-IP: [10.174.179.234] X-ClientProxiedBy: dggems702-chm.china.huawei.com (10.3.19.179) To kwepemm600017.china.huawei.com (7.193.23.234) X-Rspam-User: X-Stat-Signature: tzr7hnia7p94s89od86za1s1jxokiz44 X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: B4715160022 X-HE-Tag: 1709554510-609128 X-HE-Meta: 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 EV7pqsiV FYMyhqq/iEzJG/C1WjdGP0VFv8SgFp3AATXrWYvv7VAiJMLJGsh32Embw8bUWBV1w6xDBbKaTYqURKgKIReJx0mFt0MNrwT6Oe0lyEu0skmcV4fn0LtC+B5mFnDqaQnj87nKpIZKCXLjbssK1XZxGq5E46EtKqVaGml20ozKs/758OEEUfVBbEv585hrxmmyWvjq/+fwupy89mtyKadpzebLfCzeP0kp2XoVVmSy4RFvdllROnq6ssKjYME3fOd3Gqvcpb5kJW8lVWbZiDDezp2rD64NbIFA6SQEv X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 在 2024/3/4 19:56, David Howells 写道: > Linus Torvalds wrote: > >> Actually, I think the right model is to get rid of that horrendous >> .copy_mc field entirely. >> >> We only have one single place that uses it - that nasty core dumping >> code. And that code is *not* performance critical. >> >> And not only isn't it performance-critical, it already does all the >> core dumping one page at a time because it doesn't want to write pages >> that were never mapped into user space. >> >> So what we can do is >> >> (a) make the core dumping code *copy* the page to a good location >> with copy_mc_to_kernel() first >> >> (b) remove this horrendous .copy_mc crap entirely from iov_iter >> >> This is slightly complicated by the fact that copy_mc_to_kernel() may >> not even exist, and architectures that don't have it don't want the >> silly extra copy. So we need to abstract the "copy to temporary page" >> code a bit. But that's probably a good thing anyway in that it forces >> us to have nice interfaces. >> >> End result: something like the attached. >> >> AGAIN: THIS IS ENTIRELY UNTESTED. >> >> But hey, so was clearly all the .copy_mc code too that this removes, so... > > I like it:-) > > I've tested it by SIGQUIT'ing a number of processes and using gdb to examine > the coredumps - which seems to work - at least without the production of any > MCEs. I'm not sure how I could test it with MCEs. I'm going to test the coredump with the MCE. > > Feel free to add: > > Reviewed-by: David Howells > Tested-by: David Howells > > That said, I wonder if: > > #ifdef copy_mc_to_kernel > > should be: > > #ifdef CONFIG_ARCH_HAS_COPY_MC > > and whether it's possible to find out dynamically if MCEs can occur at all. MCE can occur during the use of a page. So i think it occurs dynamically. Thanks, Tong > > David > > .