From: Dmitry Vyukov <dvyukov@xxxxxxxxxx> Date: Wed, May 8, 2019 at 1:25 PM To: Eric Biggers Cc: syzbot, KVM list, <adrian.hunter@xxxxxxxxx>, David Miller, Artem Bityutskiy, <jbaron@xxxxxxxxxx>, Josh Poimboeuf, LKML, <linux-mtd@xxxxxxxxxxxxxxxxxxx>, Andy Lutomirski, Ingo Molnar, Peter Zijlstra, Richard Weinberger, Rik van Riel, Steven Rostedt, syzkaller-bugs, Thomas Gleixner > From: Eric Biggers <ebiggers@xxxxxxxxxx> > Date: Thu, May 2, 2019 at 4:34 AM > To: syzbot, Dmitry Vyukov, <kvm@xxxxxxxxxxxxxxx> > Cc: <adrian.hunter@xxxxxxxxx>, <davem@xxxxxxxxxxxxx>, > <dedekind1@xxxxxxxxx>, <jbaron@xxxxxxxxxx>, <jpoimboe@xxxxxxxxxx>, > <linux-kernel@xxxxxxxxxxxxxxx>, <linux-mtd@xxxxxxxxxxxxxxxxxxx>, > <luto@xxxxxxxxxx>, <mingo@xxxxxxxxxx>, <peterz@xxxxxxxxxxxxx>, > <richard@xxxxxx>, <riel@xxxxxxxxxxx>, <rostedt@xxxxxxxxxxx>, > <syzkaller-bugs@xxxxxxxxxxxxxxxx>, <tglx@xxxxxxxxxxxxx> > > > On Wed, May 01, 2019 at 07:36:05AM -0700, syzbot wrote: > > > Hello, > > > > > > syzbot found the following crash on: > > > > > > HEAD commit: baf76f0c slip: make slhc_free() silently accept an error p.. > > > git tree: upstream > > > console output: https://syzkaller.appspot.com/x/log.txt?x=1407f57f200000 > > > kernel config: https://syzkaller.appspot.com/x/.config?x=a42d110b47dd6b36 > > > dashboard link: https://syzkaller.appspot.com/bug?extid=8d9bb6157e7b379f740e > > > compiler: gcc (GCC) 9.0.0 20181231 (experimental) > > > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1266a588a00000 > > > > > > The bug was bisected to: > > > > > > commit 252153ba518ac0bcde6b7152c63380d4415bfe5d > > > Author: Eric Biggers <ebiggers@xxxxxxxxxx> > > > Date: Wed Nov 29 20:43:17 2017 +0000 > > > > > > ubifs: switch to fscrypt_prepare_setattr() > > > > > > bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=1448f588a00000 > > > final crash: https://syzkaller.appspot.com/x/report.txt?x=1648f588a00000 > > > console output: https://syzkaller.appspot.com/x/log.txt?x=1248f588a00000 > > > > > > IMPORTANT: if you fix the bug, please add the following tag to the commit: > > > Reported-by: syzbot+8d9bb6157e7b379f740e@xxxxxxxxxxxxxxxxxxxxxxxxx > > > Fixes: 252153ba518a ("ubifs: switch to fscrypt_prepare_setattr()") > > > > > > watchdog: BUG: soft lockup - CPU#0 stuck for 123s! [syz-executor.3:22023] > > > Modules linked in: > > > irq event stamp: 26556 > > > hardirqs last enabled at (26555): [<ffffffff81006673>] > > > trace_hardirqs_on_thunk+0x1a/0x1c > > > hardirqs last disabled at (26556): [<ffffffff8100668f>] > > > trace_hardirqs_off_thunk+0x1a/0x1c > > > softirqs last enabled at (596): [<ffffffff87400662>] > > > __do_softirq+0x662/0x95a kernel/softirq.c:320 > > > softirqs last disabled at (517): [<ffffffff8144e4e0>] invoke_softirq > > > kernel/softirq.c:374 [inline] > > > softirqs last disabled at (517): [<ffffffff8144e4e0>] irq_exit+0x180/0x1d0 > > > kernel/softirq.c:414 > > > CPU: 0 PID: 22023 Comm: syz-executor.3 Not tainted 5.1.0-rc6+ #89 > > > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS > > > Google 01/01/2011 > > > RIP: 0010:csd_lock_wait kernel/smp.c:108 [inline] > > > RIP: 0010:smp_call_function_single+0x13e/0x420 kernel/smp.c:302 > > > Code: 00 48 8b 4c 24 08 48 8b 54 24 10 48 8d 74 24 40 8b 7c 24 1c e8 23 fa > > > ff ff 41 89 c5 eb 07 e8 e9 87 0a 00 f3 90 44 8b 64 24 58 <31> ff 41 83 e4 01 > > > 44 89 e6 e8 54 89 0a 00 45 85 e4 75 e1 e8 ca 87 > > > RSP: 0018:ffff88809277f3e0 EFLAGS: 00000293 ORIG_RAX: ffffffffffffff13 > > > RAX: ffff8880a8bfc040 RBX: 1ffff110124efe80 RCX: ffffffff8166051c > > > RDX: 0000000000000000 RSI: ffffffff81660507 RDI: 0000000000000005 > > > RBP: ffff88809277f4b8 R08: ffff8880a8bfc040 R09: ffffed1015d25be9 > > > R10: ffffed1015d25be8 R11: ffff8880ae92df47 R12: 0000000000000003 > > > R13: 0000000000000000 R14: 0000000000000001 R15: 0000000000000000 > > > FS: 00007fd569980700(0000) GS:ffff8880ae800000(0000) knlGS:0000000000000000 > > > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > > > CR2: 00007fd56997e178 CR3: 00000000a4fd2000 CR4: 00000000001426f0 > > > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > > > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 > > > Call Trace: > > > smp_call_function_many+0x750/0x8c0 kernel/smp.c:434 > > > smp_call_function+0x42/0x90 kernel/smp.c:492 > > > on_each_cpu+0x31/0x200 kernel/smp.c:602 > > > text_poke_bp+0x107/0x19b arch/x86/kernel/alternative.c:821 > > > __jump_label_transform+0x263/0x330 arch/x86/kernel/jump_label.c:91 > > > arch_jump_label_transform+0x2b/0x40 arch/x86/kernel/jump_label.c:99 > > > __jump_label_update+0x16a/0x210 kernel/jump_label.c:389 > > > jump_label_update kernel/jump_label.c:752 [inline] > > > jump_label_update+0x1ce/0x3d0 kernel/jump_label.c:731 > > > static_key_slow_inc_cpuslocked+0x1c1/0x250 kernel/jump_label.c:129 > > > static_key_slow_inc+0x1b/0x30 kernel/jump_label.c:144 > > > kvm_arch_vcpu_init+0x6b7/0x870 arch/x86/kvm/x86.c:9068 > > > kvm_vcpu_init+0x272/0x370 arch/x86/kvm/../../../virt/kvm/kvm_main.c:320 > > > vmx_create_vcpu+0x191/0x2540 arch/x86/kvm/vmx/vmx.c:6577 > > > kvm_arch_vcpu_create+0x80/0x120 arch/x86/kvm/x86.c:8755 > > > kvm_vm_ioctl_create_vcpu arch/x86/kvm/../../../virt/kvm/kvm_main.c:2569 > > > [inline] > > > kvm_vm_ioctl+0x5ce/0x19c0 arch/x86/kvm/../../../virt/kvm/kvm_main.c:3105 > > > vfs_ioctl fs/ioctl.c:46 [inline] > > > file_ioctl fs/ioctl.c:509 [inline] > > > do_vfs_ioctl+0xd6e/0x1390 fs/ioctl.c:696 > > > ksys_ioctl+0xab/0xd0 fs/ioctl.c:713 > > > __do_sys_ioctl fs/ioctl.c:720 [inline] > > > __se_sys_ioctl fs/ioctl.c:718 [inline] > > > __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:718 > > > do_syscall_64+0x103/0x610 arch/x86/entry/common.c:290 > > > entry_SYSCALL_64_after_hwframe+0x49/0xbe > > > RIP: 0033:0x458da9 > > > Code: ad b8 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7 > > > 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff > > > 0f 83 7b b8 fb ff c3 66 2e 0f 1f 84 00 00 00 00 > > > RSP: 002b:00007fd56997fc78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010 > > > RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000458da9 > > > RDX: 0000000000000000 RSI: 000000000000ae41 RDI: 0000000000000005 > > > RBP: 000000000073bfa0 R08: 0000000000000000 R09: 0000000000000000 > > > R10: 0000000000000000 R11: 0000000000000246 R12: 00007fd5699806d4 > > > R13: 00000000004c1905 R14: 00000000004d40d0 R15: 00000000ffffffff > > > Sending NMI from CPU 0 to CPUs 1: > > > Can the KVM maintainers take a look at this? This doesn't have anything to do > > with my commit that syzbot bisected it to. > > > > +Dmitry, statistics lession: if a crash occurs only 1 in 10 times, as was the > > case here, then often it will happen 0 in 10 times by chance. syzbot needs to > > run the reproducer more times if it isn't working reliably. Otherwise it ends > > up blaming some random commit. > > Added a note to https://github.com/google/syzkaller/issues/1051 > Thanks As we increase number of instances, we increase chances of hitting unrelated bugs. E.g. take a look at the bisection log for: https://syzkaller.appspot.com/bug?extid=f14868630901fc6151d3 What is the optimum number of tests is a good question. I suspect that the current 10 instances is close to optimum. If we use significantly more we may break every other bisection on unrelated bugs...
