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[124.171.83.152]) by smtp.gmail.com with ESMTPSA id fv23sm3245567pjb.35.2020.08.06.18.43.59 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 06 Aug 2020 18:44:01 -0700 (PDT) Subject: Re: 9p/trans_fd lockup To: Dominique Martinet Cc: v9fs-developer@lists.sourceforge.net, Greg Kurz , "netdev@vger.kernel.org" References: <9d8a8abf-7968-2752-89e7-bac39ae91999@ozlabs.ru> <20200806123849.GA2640@nautica> From: Alexey Kardashevskiy Autocrypt: addr=aik@ozlabs.ru; keydata= mQINBE+rT0sBEADFEI2UtPRsLLvnRf+tI9nA8T91+jDK3NLkqV+2DKHkTGPP5qzDZpRSH6mD EePO1JqpVuIow/wGud9xaPA5uvuVgRS1q7RU8otD+7VLDFzPRiRE4Jfr2CW89Ox6BF+q5ZPV /pS4v4G9eOrw1v09lEKHB9WtiBVhhxKK1LnUjPEH3ifkOkgW7jFfoYgTdtB3XaXVgYnNPDFo PTBYsJy+wr89XfyHr2Ev7BB3Xaf7qICXdBF8MEVY8t/UFsesg4wFWOuzCfqxFmKEaPDZlTuR tfLAeVpslNfWCi5ybPlowLx6KJqOsI9R2a9o4qRXWGP7IwiMRAC3iiPyk9cknt8ee6EUIxI6 t847eFaVKI/6WcxhszI0R6Cj+N4y+1rHfkGWYWupCiHwj9DjILW9iEAncVgQmkNPpUsZECLT WQzMuVSxjuXW4nJ6f4OFHqL2dU//qR+BM/eJ0TT3OnfLcPqfucGxubhT7n/CXUxEy+mvWwnm 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Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20200806123849.GA2640@nautica> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 06/08/2020 22:38, Dominique Martinet wrote: > Alexey Kardashevskiy wrote on Thu, Aug 06, 2020: >> I am seeing another bug in 9p under syzkaller, the reprocase is: >> >> r0 = open$dir(&(0x7f0000000040)='./file0\x00', 0x88142, 0x182) >> >> r1 = openat$null(0xffffffffffffff9c, &(0x7f0000000640)='/dev/null\x00', >> 0x0, 0x0) >> mount$9p_fd(0x0, &(0x7f0000000000)='./file0\x00', >> &(0x7f00000000c0)='9p\x00', 0x0, &(0x7f0000000100)={'trans=fd,', >> {'rfdno', 0x3d, r1}, 0x2$, {'wfdno', 0x3d, r0}}) >> >> >> >> The default behaviour of syzkaller is to call syscalls concurrently (I >> think), at least it forks by default and executes the same sequence in >> both threads. >> >> In this example both threads makes it to: >> >> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/net/9p/client.c?h=v5.8#n757 >> >> and sit there with the only difference which is thread#1 goes via >> >> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/net/9p/client.c?h=v5.8#n767 >> >> I am pretty sure things should not have gone that far but I cannot >> clearly see what needs fixing. Ideas? Thanks, > > Unkillable threads there happen with the current p9_client_rpc when > there is no real server (or server bug etc); the code is really stupid. > > Basically what happens is that when you send a first signal (^C or > whatever), the function catches the signal, sends a flush, and > indefinitely waits for the flush to come back. > If you send another signal there no more flush comes but it goes back to > waiting -- it's using wait_event_killable but it's a lie it's not really > killable it just loops on that wait until the flush finally comes, which > will never come in your case. > (the rpc that came by the way is probably version or whatever is first > done on mount) > > > Dmitry reported that to me ages ago and I have a fix which is just to > stop waiting for the flush -- just make it asynchronous, send and > forget. That removes the whole signal handling logic and it won't hang > there anymore. > > I sent the patches to the list last year, but didn't get much feedback > and didn't have time to run all the tests I wanted to run on it. > > > I have some free time at the end of the month so I was planning to > finish it for 5.10 (e.g. won't send it for 5.9 but once 5.9 initial > merge window passed leave it in -next for a couple of months and push it > for 5.10), so your timing is pretty good :) > An extra pair of eyes would be more than appreciated. > > You can find the original mails there: > https://lore.kernel.org/lkml/1544532108-21689-3-git-send-email-asmadeus@codewreck.org/ > > They're also in my 9p-test branch on git://github.com/martinetd/linux Thanks for the patches, they fix my case indeed and I'll continue with them, let's see what else syzkaller finds :) > > > Cheers & thanks for the attention, > -- Alexey