From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-12.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4A363C432BE for ; Tue, 10 Aug 2021 22:03:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 31F6660FDA for ; Tue, 10 Aug 2021 22:03:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235057AbhHJWDo (ORCPT ); Tue, 10 Aug 2021 18:03:44 -0400 Received: from mail.cybernetics.com ([173.71.130.66]:39348 "EHLO mail.cybernetics.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234814AbhHJWDk (ORCPT ); Tue, 10 Aug 2021 18:03:40 -0400 X-ASG-Debug-ID: 1628632116-0fb3b001bfb8450001-xx1T2L Received: from cybernetics.com ([10.10.4.126]) by mail.cybernetics.com with ESMTP id lBBttwPgVpb4DYE9; Tue, 10 Aug 2021 17:48:36 -0400 (EDT) X-Barracuda-Envelope-From: tonyb@cybernetics.com X-Barracuda-RBL-Trusted-Forwarder: 10.10.4.126 X-ASG-Whitelist: Client DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=cybernetics.com; s=mail; bh=+hK5EuG8CU750itG1TX0GBRlkn+Cy53TYseDIf+v+sI=; h=Content-Language:Content-Transfer-Encoding:Content-Type:In-Reply-To: MIME-Version:Date:Message-ID:References:Cc:To:Subject:From; b=LpPQsr5mGtBt+Cs xj9KVvUl5T0RXMWLZntt1LBXTLCfK2DE9s+D2IT0x6m8tWeRnKY//F8NuchNEIa5DUtU9suioq6Np L9kyMAX8XC4fxV/aaEuZ1aMLXoozEISqvjDAAHRUVQTLLlfF4NmubneZneTsphIxgBIWiaD2ioDTz X0= Received: from [10.157.2.224] (HELO [192.168.200.1]) by cybernetics.com (CommuniGate Pro SMTP 6.2.14) with ESMTPS id 11062327; Tue, 10 Aug 2021 17:48:36 -0400 From: Tony Battersby X-Barracuda-RBL-Trusted-Forwarder: 10.157.2.224 Subject: Re: [PATCH] coredump: Limit what can interrupt coredumps To: Olivier Langlois , "Eric W. Biederman" , Oleg Nesterov X-ASG-Orig-Subj: Re: [PATCH] coredump: Limit what can interrupt coredumps Cc: Linus Torvalds , Linux Kernel Mailing List , linux-fsdevel , io-uring , Alexander Viro , Jens Axboe , "Pavel Begunkov>" References: <198e912402486f66214146d4eabad8cb3f010a8e.camel@trillion01.com> <87eeda7nqe.fsf@disp2133> <87pmwt6biw.fsf@disp2133> <87czst5yxh.fsf_-_@disp2133> <87y2bh4jg5.fsf@disp2133> <87sg1p4h0g.fsf_-_@disp2133> <20210614141032.GA13677@redhat.com> <87pmwmn5m0.fsf@disp2133> <4d93d0600e4a9590a48d320c5a7dd4c54d66f095.camel@trillion01.com> Message-ID: <8af373ec-9609-35a4-f185-f9bdc63d39b7@cybernetics.com> Date: Tue, 10 Aug 2021 17:48:36 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: <4d93d0600e4a9590a48d320c5a7dd4c54d66f095.camel@trillion01.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Content-Language: en-US X-Barracuda-Connect: UNKNOWN[10.10.4.126] X-Barracuda-Start-Time: 1628632116 X-Barracuda-URL: https://10.10.4.122:443/cgi-mod/mark.cgi X-Barracuda-BRTS-Status: 1 X-Virus-Scanned: by bsmtpd at cybernetics.com X-Barracuda-Scan-Msg-Size: 6264 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 8/5/21 9:06 AM, Olivier Langlois wrote: > On Tue, 2021-06-15 at 17:08 -0500, Eric W. Biederman wrote: >> Oleg Nesterov writes: >> >>>> --- a/fs/coredump.c >>>> +++ b/fs/coredump.c >>>> @@ -519,7 +519,7 @@ static bool dump_interrupted(void) >>>>          * but then we need to teach dump_write() to restart and >>>> clear >>>>          * TIF_SIGPENDING. >>>>          */ >>>> -       return signal_pending(current); >>>> +       return fatal_signal_pending(current) || freezing(current); >>>>  } >>> Well yes, this is what the comment says. >>> >>> But note that there is another reason why dump_interrupted() returns >>> true >>> if signal_pending(), it assumes thagt __dump_emit()->__kernel_write() >>> may >>> fail anyway if signal_pending() is true. Say, pipe_write(), or iirc >>> nfs, >>> perhaps something else... >>> >>> That is why zap_threads() clears TIF_SIGPENDING. Perhaps it should >>> clear >>> TIF_NOTIFY_SIGNAL as well and we should change io-uring to not abuse >>> the >>> dumping threads? >>> >>> Or perhaps we should change __dump_emit() to clear signal_pending() >>> and >>> restart __kernel_write() if it fails or returns a short write. >>> >>> Otherwise the change above doesn't look like a full fix to me. >> Agreed.  The coredump to a pipe will still be short.  That needs >> something additional. >> >> The problem Olivier Langlois reported was >> core dumps coming up short because TIF_NOTIFY_SIGNAL was being >> set during a core dump. >> >> We can see this with pipe_write returning -ERESTARTSYS >> on a full pipe if signal_pending which includes TIF_NOTIFY_SIGNAL >> is true. >> >> Looking further if the thread that is core dumping initiated >> any io_uring work then io_ring_exit_work will use task_work_add >> to request that thread clean up it's io_uring state. >> >> Perhaps we can put a big comment in dump_emit and if we >> get back -ERESTARTSYS run tracework_notify_signal.  I am not >> seeing any locks held at that point in the coredump, so it >> should be safe.  The coredump is run inside of file_start_write >> which is the only potential complication. >> >> >> >> The code flow is complicated but it looks like the entire >> point of the exercise is to call io_uring_del_task_file >> on the originating thread.  I suppose that keeps the >> locking of the xarray in io_uring_task simple. >> >> >> Hmm.   All of this comes from io_uring_release. >> How do we get to io_uring_release?  The coredump should >> be catching everything in exit_mm before exit_files? >> >> Confused and hopeful someone can explain to me what is going on, >> and perhaps simplify it. >> >> Eric > Hi all, > > I didn't forgot about this remaining issue and I have kept thinking > about it on and off. > > I did try the following on 5.12.19: > > diff --git a/fs/coredump.c b/fs/coredump.c > index 07afb5ddb1c4..614fe7a54c1a 100644 > --- a/fs/coredump.c > +++ b/fs/coredump.c > @@ -41,6 +41,7 @@ > #include > #include > #include > +#include > > #include > #include > @@ -625,6 +626,8 @@ void do_coredump(const kernel_siginfo_t *siginfo) > need_suid_safe = true; > } > > + io_uring_files_cancel(current->files); > + > retval = coredump_wait(siginfo->si_signo, &core_state); > if (retval < 0) > goto fail_creds; > -- > 2.32.0 > > with my current understanding, io_uring_files_cancel is supposed to > cancel everything that might set the TIF_NOTIFY_SIGNAL. > > I must report that in my testing with generating a core dump through a > pipe with the modif above, I still get truncated core dumps. > > systemd is having a weird error: > [ 2577.870742] systemd-coredump[4056]: Failed to get COMM: No such > process > > and nothing is captured > > so I have replaced it with a very simple shell: > $ cat /proc/sys/kernel/core_pattern > |/home/lano1106/bin/pipe_core.sh %e %p > > ~/bin $ cat pipe_core.sh > #!/bin/sh > > cat > /home/lano1106/core/core.$1.$2 > > BFD: warning: /home/lano1106/core/core.test.10886 is truncated: > expected core file size >= 24129536, found: 61440 > > I conclude from my attempt that maybe io_uring_files_cancel is not 100% > cleaning everything that it should clean. > > > I just ran into this problem also - coredumps from an io_uring program to a pipe are truncated.  But I am using kernel 5.10.57, which does NOT have commit 12db8b690010 ("entry: Add support for TIF_NOTIFY_SIGNAL") or commit 06af8679449d ("coredump: Limit what can interrupt coredumps").  Kernel 5.4 works though, so I bisected the problem to commit f38c7e3abfba ("io_uring: ensure async buffered read-retry is setup properly") in kernel 5.9.  Note that my io_uring program uses only async buffered reads, which may be why this particular commit makes a difference to my program. My io_uring program is a multi-purpose long-running program with many threads.  Most threads don't use io_uring but a few of them do.  Normally, my core dumps are piped to a program so that they can be compressed before being written to disk, but I can also test writing the core dumps directly to disk.  This is what I have found: *) Unpatched 5.10.57: if a thread that doesn't use io_uring triggers a coredump, the core file is written correctly, whether it is written to disk or piped to a program, even if another thread is using io_uring at the same time. *) Unpatched 5.10.57: if a thread that uses io_uring triggers a coredump, the core file is truncated, whether written directly to disk or piped to a program. *) 5.10.57+backport 06af8679449d: if a thread that uses io_uring triggers a coredump, and the core is written directly to disk, then it is written correctly. *) 5.10.57+backport 06af8679449d: if a thread that uses io_uring triggers a coredump, and the core is piped to a program, then it is truncated. *) 5.10.57+revert f38c7e3abfba: core dumps are written correctly, whether written directly to disk or piped to a program. Tony Battersby Cybernetics