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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=K1r/myxxqbnuDfR7HdmZaSGgM2+xgRSfXaw7wBy4btlELsZAHxZYWESeZRIp72MLi5 i4rhfJI/H8qdgf04TXwVTv08lCudPUPFkmCzqD1/nnCJMwDsOjTFJisxB6OHbDGwOvIi PIQOG8CVp0mvy+R1uj/z61JgsoQCX0srBb+9lOOoJfK/pNQq9lDYAyB5aqIz/RsvdBx6 v6exH5/GN7P54VWsOq0+HaJDxFERgqOnZH4Sg4NlVr5x++Lf0kDwaob0R8Uw9Kw2+uJm dORJ7HvpZyv0TEee6EJ2bDRFuyl7Uy+4BNDcu4ueyV1ObYgdADfeKD4dw0gvOQJzywkZ 2eRw== X-Gm-Message-State: APjAAAWueGYQ1vmPVBDfrZGMwptL9HAbiNGi4sq4xZUGgNg8jAFEPuJ7 Y4E3589dc9RdLD9oBeOqHIBHNCVL6rXuPEJhfiKF6A== 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-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@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?