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=-11.5 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 D1F8AC432BE for ; Mon, 9 Aug 2021 13:46:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id AF33260F25 for ; Mon, 9 Aug 2021 13:46:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234333AbhHINrA (ORCPT ); Mon, 9 Aug 2021 09:47:00 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:40202 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234155AbhHINq6 (ORCPT ); Mon, 9 Aug 2021 09:46:58 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1628516797; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=kC60/FWvUwVd7y01o36qa1ToUR0hILQPRSMtA/mfOk4=; b=MXs95t3Tfp8QCDmiftr8m5T/NMPGoLy+pfhVTakq44+nfeoCA1RDxgsB1w6Om77WKxwjdM Q+5Qk+lViLgNSZIHJD6yWiJSdoBVCJGBKTokcWlJcmhm6HoC7zMIHfeP1+w518YXaghSlf CC4Z7kaiR/G1+oNkZq38LNOvmjKJfI0= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-592-WeHJt-ooMMOa3Q7ID4zj0Q-1; Mon, 09 Aug 2021 09:46:36 -0400 X-MC-Unique: WeHJt-ooMMOa3Q7ID4zj0Q-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id A9CF7190A7A0; Mon, 9 Aug 2021 13:46:34 +0000 (UTC) Received: from segfault.boston.devel.redhat.com (segfault.boston.devel.redhat.com [10.19.60.26]) by smtp.corp.redhat.com (Postfix) with ESMTPS id E22295D6A1; Mon, 9 Aug 2021 13:46:33 +0000 (UTC) From: Jeff Moyer To: Dmitry Vyukov Cc: syzbot , bcrl@kvack.org, linux-aio@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com, viro@zeniv.linux.org.uk Subject: Re: [syzbot] INFO: task hung in sys_io_destroy References: <0000000000007db08f05c79fc81f@google.com> X-PGP-KeyID: 1F78E1B4 X-PGP-CertKey: F6FE 280D 8293 F72C 65FD 5A58 1FF8 A7CA 1F78 E1B4 Date: Mon, 09 Aug 2021 09:47:57 -0400 In-Reply-To: (Dmitry Vyukov's message of "Mon, 9 Aug 2021 11:24:22 +0200") Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Dmitry Vyukov writes: > On Fri, 6 Aug 2021 at 22:39, Jeff Moyer wrote: >> >> syzbot writes: >> >> > Hello, >> > >> > syzbot found the following issue on: >> > >> > HEAD commit: 1d67c8d993ba Merge tag 'soc-fixes-5.14-1' of git://git.ker.. >> > git tree: upstream >> > console output: https://syzkaller.appspot.com/x/log.txt?x=11b40232300000 >> > kernel config: https://syzkaller.appspot.com/x/.config?x=f1b998c1afc13578 >> > dashboard link: https://syzkaller.appspot.com/bug?extid=d40a01556c761b2cb385 >> > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=12453812300000 >> > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=11225922300000 >> > >> > Bisection is inconclusive: the issue happens on the oldest tested release. >> > >> > bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=127cac6a300000 >> > final oops: https://syzkaller.appspot.com/x/report.txt?x=117cac6a300000 >> > console output: https://syzkaller.appspot.com/x/log.txt?x=167cac6a300000 >> > >> > IMPORTANT: if you fix the issue, please add the following tag to the commit: >> > Reported-by: syzbot+d40a01556c761b2cb385@syzkaller.appspotmail.com >> > >> > INFO: task syz-executor299:8807 blocked for more than 143 seconds. >> > Not tainted 5.14.0-rc1-syzkaller #0 >> > "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. >> > task:syz-executor299 state:D stack:29400 pid: 8807 ppid: 8806 flags:0x00000000 >> > Call Trace: >> > context_switch kernel/sched/core.c:4683 [inline] >> > __schedule+0x93a/0x26f0 kernel/sched/core.c:5940 >> > schedule+0xd3/0x270 kernel/sched/core.c:6019 >> > schedule_timeout+0x1db/0x2a0 kernel/time/timer.c:1854 >> > do_wait_for_common kernel/sched/completion.c:85 [inline] >> > __wait_for_common kernel/sched/completion.c:106 [inline] >> > wait_for_common kernel/sched/completion.c:117 [inline] >> > wait_for_completion+0x176/0x280 kernel/sched/completion.c:138 >> > __do_sys_io_destroy fs/aio.c:1402 [inline] >> > __se_sys_io_destroy fs/aio.c:1380 [inline] >> > __x64_sys_io_destroy+0x17e/0x1e0 fs/aio.c:1380 >> > do_syscall_x64 arch/x86/entry/common.c:50 [inline] >> > do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80 >> > entry_SYSCALL_64_after_hwframe+0x44/0xae >> >> The reproducer is creating a thread, issuing a IOCB_CMD_PREAD from a >> pipe in that thread, and then calling io_destroy from another thread. >> Because there is no writer on the other end of the pipe, the read will >> block. Note that it also is not submitted asynchronously, as that's not >> supported. >> >> io_destroy is "hanging" because it's waiting for the read to finish. If >> the read thread is killed, cleanup happens as usual. I'm not sure I >> could classify this as a kernel bug. > > Hi Jeff, > > Thanks for looking into this. I suspect the reproducer may create a > fork bomb that DoSed the kernel so that it can't make progress for 140 > seconds. FTR, I've added it to > https://github.com/google/syzkaller/issues/498#issuecomment-895071514 > to take a closer look. No, I described exactly what happens. You can reproduce the hung task timeout with a much simpler program, attached below. Cheers, Jeff #define _GNU_SOURCE #include #include #include #include #include #include #include #include #define BUFSZ 512 void * submit_thread(void *arg) { io_context_t *ctx = arg; int ret; int fds[2]; char buf[BUFSZ]; struct iocb iocb, *iocbp = &iocb; ret = pipe(fds); if (ret) { perror("pipe"); exit(1); } io_prep_pread(iocbp, fds[0], buf, BUFSZ, 0); ret = io_submit(*ctx, 1, &iocbp); if (ret != 1) { printf("io_submit failed with %d\n", ret); exit(1); } /* NOTREACHED */ printf("Read submitted.\n"); return 0; } int main(void) { int ret; io_context_t ctx; pthread_t pth; memset(&ctx, 0, sizeof(ctx)); ret = io_setup(1, &ctx); if (ret) { printf("io_setup failed with %d\n", ret); exit(1); } ret = pthread_create(&pth, NULL, submit_thread, &ctx); if (ret) { perror("pthread_create"); exit(1); } usleep(1000); /* give the thread time to run */ ret = io_destroy(ctx); if (ret) { printf("io_destroy failed with %d\n", ret); exit(1); } exit(0); }