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h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=TkFN6mZO3jzTkDHV/Hmyrf49PT5DaBxkKPm0fJ0JB7Y=; b=KwoJeheqzbp5vNxkxxaorvfO9uNXFfeA1s1iZHyPYTxcmJLLqRYMqj2R3pxMJYH3y3 gbPde4KulvVEiMQImI26dLu5oYcjMkyiBcTl2a9J2BHWwqcHeunzdbthBIYZ7Vo6d+hO MJcFda1lV1XZERDQp6c8sBLKnYSMhnj8E7MrWtvg0MhsVl2SeD2AouzTOWZgQLzBEm7V Zf/zmkdwA/KyE8o72KVQcycHjbijVh8aYZs9hWaqNcvEws/Cpf3UOQiWckr7NHCivvPa ZVzCsiAP5wiSuA/W6ogc4yyidcGOYj3zyL4k4kLDD8ZG/rOkazHBmHCJTODHfh91LRmm hFCw== X-Gm-Message-State: APjAAAVdnXANj56Z5Qgzx/lFAfV4ZU9gGmN+Kap9UlFkwyhGlLMocdVz bQ9nF+M1xr+a+xAUWp/uEPjt6tTgaJVIYVGk+4vSMw== X-Google-Smtp-Source: APXvYqwu0jZl1WMHUfwjCc8eNXQNMtRUY6cTb9zGogIf9gHJFZeSly1uN/MHdmpZevTU/Dnp0Zw/aw7coEIvqtnVR94= X-Received: by 2002:a24:3281:: with SMTP id j123mr3898152ita.166.1553325407533; Sat, 23 Mar 2019 00:16:47 -0700 (PDT) MIME-Version: 1.0 References: <000000000000cd1e2205785951c2@google.com> <00000000000088ea3e0584b5872d@google.com> In-Reply-To: <00000000000088ea3e0584b5872d@google.com> From: Dmitry Vyukov Date: Sat, 23 Mar 2019 08:16:36 +0100 Message-ID: Subject: Re: possible deadlock in __generic_file_fsync To: syzbot Cc: Andreas Dilger , linux-ext4@vger.kernel.org, linux-fsdevel , LKML , syzkaller-bugs , Linus Torvalds , "Theodore Ts'o" , Al Viro Content-Type: text/plain; charset="UTF-8" Sender: linux-ext4-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-ext4@vger.kernel.org On Fri, Mar 22, 2019 at 10:28 PM syzbot wrote: > > syzbot has bisected this bug to: > > commit 9022ada8ab6f1f1a932a3c93815061042e6548a5 > Author: Linus Torvalds > Date: Fri Aug 24 20:16:36 2018 +0000 > > Merge branch 'for-4.19' of > git://git.kernel.org/pub/scm/linux/kernel/git/tj/wq > > bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=15330437200000 > start commit: 270b77a0 Merge tag 'drm-fixes-2018-10-20-1' of git://anong.. > git tree: upstream > final crash: https://syzkaller.appspot.com/x/report.txt?x=17330437200000 > console output: https://syzkaller.appspot.com/x/log.txt?x=13330437200000 > kernel config: https://syzkaller.appspot.com/x/.config?x=b3f55cb3dfcc6c33 > dashboard link: https://syzkaller.appspot.com/bug?extid=5cd33f0e6abe2bb3e397 > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1436fc45400000 > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=11058e2d400000 > > Reported-by: syzbot+5cd33f0e6abe2bb3e397@syzkaller.appspotmail.com > Fixes: 9022ada8ab6f ("Merge branch 'for-4.19' of > git://git.kernel.org/pub/scm/linux/kernel/git/tj/wq") > > For information about bisection process see: https://goo.gl/tpsmEJ#bisection This is a lockdep-detected bug, but it is reproduced with very low probability: testing commit 270b77a0f30e7bc61a9081b86d74dbb62fa6a69d with gcc (GCC) 8.1.0 run #0: crashed: possible deadlock in __generic_file_fsync run #1: OK run #2: OK run #3: OK run #4: OK run #5: OK run #6: OK run #7: OK run #8: OK run #9: OK I would expect that for lockdep it's only enough to trigger each path involved in the deadlock once. Why is it so hard to reproduce then? Is it something to improve in lockdep?