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Fri, 7 Mar 2025 15:11:10 +0200 (EET) (envelope-from jimsiak@cslab.ece.ntua.gr) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=cslab.ece.ntua.gr; s=ntuawebmail; t=1741353072; bh=oVpPMTXsg3bi3hi70RsuLhS3qOSUxyPhr8tXaNh8K5g=; h=Date:From:To:Cc:Subject:In-Reply-To:References; b=T2zf5W+wLagiy8P5No0no31FHpQrRE+eN4n0FMpeIzccfnKBL8kHzWJ2S1fsSuBN2 BCo/GrEVNabskXcfd8ERSuUqZS/N27ndecgWKkXsU/Bx7r+yYtbLRKoLwxiBKODdr3 zc9xoEfP9x+yiASASJmwRRtde56CgkWeSGCd3EAc= X-Authentication-Warning: webmail.mail.ntua.gr: Host [IPv6:2001:648:2000:de:0:0:0:247] claimed to be webmail.ntua.gr MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Date: Fri, 07 Mar 2025 15:11:09 +0200 From: jimsiak To: Jinjiang Tu Cc: peterx@redhat.com, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk, linux-mm@kvack.org, wangkefeng.wang@huawei.com Subject: Re: Using userfaultfd with KVM's async page fault handling causes processes to hung waiting for mmap_lock to be released In-Reply-To: <46ac83f7-d3e0-b667-7352-d853938c9fc9@huawei.com> References: <79375b71-db2e-3e66-346b-254c90d915e2@cslab.ece.ntua.gr> <20250307072133.3522652-1-tujinjiang@huawei.com> <46ac83f7-d3e0-b667-7352-d853938c9fc9@huawei.com> Message-ID: X-Sender: jimsiak@cslab.ece.ntua.gr User-Agent: Roundcube Webmail/1.3.10 X-Greylist: Sender passed SPF test, not delayed by milter-greylist-4.6.2 (achilles.noc.ntua.gr [147.102.222.210]); Fri, 07 Mar 2025 15:11:13 +0200 (EET) X-Rspamd-Server: rspam02 X-Stat-Signature: cgan6x8py4hpyzrrk8oug6aqwekuqes6 X-Rspamd-Queue-Id: B11FC100016 X-Rspam-User: X-HE-Tag: 1741353092-86970 X-HE-Meta: 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 Ur67ahbV 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.394423, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hi, From my side, I managed to avoid the freezing of processes with the following change in function userfaultfd_release() in file fs/userfaultfd.c (https://elixir.bootlin.com/linux/v5.13/source/fs/userfaultfd.c#L842): I moved the following command from line 851: WRITE_ONCE(ctx->released, true); (https://elixir.bootlin.com/linux/v5.13/source/fs/userfaultfd.c#L851) to line 905, that is exactly before the functions returns 0. That simple workaround worked for my use case but I am far from sure that is a correct/sufficient fix for the problem at hand. Best Regards, Dimitris Στις 07/03/2025 10:07, Jinjiang Tu έγραψε: > cc Peter Xu > > 在 2025/3/7 15:21, Jinjiang Tu 写道: >> Hi, >> >> I encountered the same issue too. In my scenario, GUP is called by >> mlockall() >> syscall. >> >> Is there a solution to fix it? >> >> Thanks. >>