On 2019/09/25 9:56, syzbot wrote: > Hello, > > syzbot found the following crash on: > > HEAD commit: f7c3bf8f Merge tag 'gfs2-for-5.4' of git://git.kernel.org/.. > git tree: upstream > console output: https://syzkaller.appspot.com/x/log.txt?x=15f5baf9600000 > kernel config: https://syzkaller.appspot.com/x/.config?x=50d4af03d68a470c > dashboard link: https://syzkaller.appspot.com/bug?extid=b2c197f98f86543b69c8 > compiler: clang version 9.0.0 (/home/glider/llvm/clang > 80fee25776c2fb61e74c1ecb1a523375c2500b69) > > Unfortunately, I don't have any reproducer for this crash yet. > > IMPORTANT: if you fix the bug, please add the following tag to the commit: > Reported-by: syzbot+b2c197f98f86543b69c8@xxxxxxxxxxxxxxxxxxxxxxxxx Oh... When the queue is initialized and the elevator initialization done by elevator_init_mq() is executed without the queue sysfs lock held. In that step, if the elevator initialization fails, blk_mq_sched_free_requests() is called and will trip on the lockdep_assert_held(&q->sysfs_lock) check on entry. I guess that is what is causing the crash ? But I thought lockdep_assert_held() only spits out warnings... Ming, Your patch c48dac137a62 ("block: don't hold q->sysfs_lock in elevator_init_mq") removed the sysfs_lock use in elevator_init_mq(). With that, should we move the lockdep_assert_held(&q->sysfs_lock) call out of blk_mq_sched_free_requests() and directly call it lockdep before calling that function (that's ugly) or do you see a nice trick for handling the special case that is the first initialization ? Cheers. > > ------------[ cut here ]------------ > WARNING: CPU: 1 PID: 25817 at block/blk-mq-sched.c:558 > blk_mq_sched_free_requests block/blk-mq-sched.c:558 [inline] > WARNING: CPU: 1 PID: 25817 at block/blk-mq-sched.c:558 > blk_mq_init_sched+0xad6/0xc00 block/blk-mq-sched.c:543 > Kernel panic - not syncing: panic_on_warn set ... > CPU: 1 PID: 25817 Comm: syz-executor.4 Not tainted 5.3.0+ #0 > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS > Google 01/01/2011 > Call Trace: > __dump_stack lib/dump_stack.c:77 [inline] > dump_stack+0x1d8/0x2f8 lib/dump_stack.c:113 > panic+0x25c/0x799 kernel/panic.c:219 > __warn+0x22f/0x230 kernel/panic.c:576 > report_bug+0x190/0x290 lib/bug.c:186 > fixup_bug arch/x86/kernel/traps.c:179 [inline] > do_error_trap+0xd7/0x440 arch/x86/kernel/traps.c:272 > do_invalid_op+0x36/0x40 arch/x86/kernel/traps.c:291 > invalid_op+0x23/0x30 arch/x86/entry/entry_64.S:1028 > RIP: 0010:blk_mq_sched_free_requests block/blk-mq-sched.c:558 [inline] > RIP: 0010:blk_mq_init_sched+0xad6/0xc00 block/blk-mq-sched.c:543 > Code: f6 e8 9e 03 00 00 49 83 c6 10 4c 89 f7 e8 82 08 37 04 e9 ce fd ff ff > e8 c8 81 3f fe 48 c7 c7 72 5c 35 88 31 c0 e8 1d ae 28 fe <0f> 0b e9 ce f9 > ff ff e8 ae 81 3f fe 48 c7 c7 72 5c 35 88 31 c0 e8 > RSP: 0018:ffff88802225fbb8 EFLAGS: 00010246 > RAX: 0000000000000024 RBX: 0000000000000000 RCX: 489d2508ed9c7100 > RDX: ffffc9000e9a6000 RSI: 0000000000009af7 RDI: 0000000000009af8 > RBP: ffff88802225fc50 R08: ffffffff815c9744 R09: ffffed1015d66090 > R10: ffffed1015d66090 R11: 0000000000000000 R12: dffffc0000000000 > R13: ffff888026958990 R14: ffff888026958080 R15: ffff8880269580d0 > elevator_init_mq+0x317/0x450 block/elevator.c:719 > __device_add_disk+0x6d/0x1140 block/genhd.c:705 > device_add_disk+0x2a/0x40 block/genhd.c:763 > add_disk include/linux/genhd.h:429 [inline] > loop_add+0x5d1/0x780 drivers/block/loop.c:2051 > loop_control_ioctl+0x422/0x640 drivers/block/loop.c:2174 > do_vfs_ioctl+0x744/0x1730 fs/ioctl.c:46 > ksys_ioctl fs/ioctl.c:713 [inline] > __do_sys_ioctl fs/ioctl.c:720 [inline] > __se_sys_ioctl fs/ioctl.c:718 [inline] > __x64_sys_ioctl+0xe3/0x120 fs/ioctl.c:718 > do_syscall_64+0xf7/0x1c0 arch/x86/entry/common.c:290 > entry_SYSCALL_64_after_hwframe+0x49/0xbe > RIP: 0033:0x459a09 > Code: fd b7 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 cb b7 fb ff c3 66 2e 0f 1f 84 00 00 00 00 > RSP: 002b:00007fce60497c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010 > RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000459a09 > RDX: 0000000000000000 RSI: 0000000000004c80 RDI: 0000000000000006 > RBP: 000000000075bfc8 R08: 0000000000000000 R09: 0000000000000000 > R10: 0000000000000000 R11: 0000000000000246 R12: 00007fce604986d4 > R13: 00000000004c3118 R14: 00000000004d69f8 R15: 00000000ffffffff > Kernel Offset: disabled > Rebooting in 86400 seconds.. > > > --- > This bug is generated by a bot. It may contain errors. > See https://goo.gl/tpsmEJ for more information about syzbot. > syzbot engineers can be reached at syzkaller@xxxxxxxxxxxxxxxx. > > syzbot will keep track of this bug report. See: > https://goo.gl/tpsmEJ#status for how to communicate with syzbot. > -- Damien Le Moal Western Digital Research
