I think this is a false positive due to the cycling through different bd_mutex instances. I think my next big series aimed at 5.11 will fix this as a side effect, so I plan to ignore this for now, but will test the reproducer with the follow on work applied eventually. On Tue, Nov 17, 2020 at 02:30:20AM -0800, syzbot wrote: > Hello, > > syzbot found the following issue on: > > HEAD commit: 03430750 Add linux-next specific files for 20201116 > git tree: linux-next > console output: https://syzkaller.appspot.com/x/log.txt?x=1642f486500000 > kernel config: https://syzkaller.appspot.com/x/.config?x=a1c4c3f27041fdb8 > dashboard link: https://syzkaller.appspot.com/bug?extid=fd01c5d29a476390728d > compiler: gcc (GCC) 10.1.0-syz 20200507 > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=14646461500000 > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=17dc946a500000 > > IMPORTANT: if you fix the issue, please add the following tag to the commit: > Reported-by: syzbot+fd01c5d29a476390728d@xxxxxxxxxxxxxxxxxxxxxxxxx > > ====================================================== > WARNING: possible circular locking dependency detected > 5.10.0-rc3-next-20201116-syzkaller #0 Not tainted > ------------------------------------------------------ > syz-executor541/8491 is trying to acquire lock: > ffffffff8bd213a8 (brd_devices_mutex){+.+.}-{3:3}, at: brd_probe+0x31/0x250 drivers/block/brd.c:434 > > but task is already holding lock: > ffffffff8bac3508 (major_names_lock){+.+.}-{3:3}, at: request_gendisk_module block/genhd.c:976 [inline] > ffffffff8bac3508 (major_names_lock){+.+.}-{3:3}, at: get_gendisk+0x3c8/0x6a0 block/genhd.c:1029 > > which lock already depends on the new lock. > > > the existing dependency chain (in reverse order) is: > > -> #3 (major_names_lock){+.+.}-{3:3}: > __mutex_lock_common kernel/locking/mutex.c:956 [inline] > __mutex_lock+0x134/0x1110 kernel/locking/mutex.c:1103 > __register_blkdev+0x2b/0x390 block/genhd.c:449 > register_mtd_blktrans+0x85/0x3c0 drivers/mtd/mtd_blkdevs.c:534 > do_one_initcall+0x103/0x650 init/main.c:1222 > do_initcall_level init/main.c:1295 [inline] > do_initcalls init/main.c:1311 [inline] > do_basic_setup init/main.c:1331 [inline] > kernel_init_freeable+0x600/0x684 init/main.c:1531 > kernel_init+0xd/0x1b8 init/main.c:1420 > ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:296 > > -> #2 (mtd_table_mutex){+.+.}-{3:3}: > __mutex_lock_common kernel/locking/mutex.c:956 [inline] > __mutex_lock+0x134/0x1110 kernel/locking/mutex.c:1103 > blktrans_open+0x69/0x600 drivers/mtd/mtd_blkdevs.c:212 > __blkdev_get+0x80f/0x1870 fs/block_dev.c:1494 > blkdev_get+0xd1/0x240 fs/block_dev.c:1634 > blkdev_open+0x21d/0x2b0 fs/block_dev.c:1751 > do_dentry_open+0x4b9/0x11b0 fs/open.c:817 > do_open fs/namei.c:3252 [inline] > path_openat+0x1b9a/0x2730 fs/namei.c:3369 > do_filp_open+0x17e/0x3c0 fs/namei.c:3396 > do_sys_openat2+0x16d/0x420 fs/open.c:1168 > do_sys_open fs/open.c:1184 [inline] > __do_sys_open fs/open.c:1192 [inline] > __se_sys_open fs/open.c:1188 [inline] > __x64_sys_open+0x119/0x1c0 fs/open.c:1188 > do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46 > entry_SYSCALL_64_after_hwframe+0x44/0xa9 > > -> #1 (&bdev->bd_mutex){+.+.}-{3:3}: > __mutex_lock_common kernel/locking/mutex.c:956 [inline] > __mutex_lock+0x134/0x1110 kernel/locking/mutex.c:1103 > __blkdev_get+0x457/0x1870 fs/block_dev.c:1479 > blkdev_get+0xd1/0x240 fs/block_dev.c:1634 > blkdev_get_by_dev+0x3b/0x70 fs/block_dev.c:1715 > disk_scan_partitions block/genhd.c:677 [inline] > register_disk block/genhd.c:727 [inline] > __device_add_disk+0xe02/0x1250 block/genhd.c:814 > add_disk include/linux/genhd.h:295 [inline] > brd_init+0x2af/0x475 drivers/block/brd.c:518 > do_one_initcall+0x103/0x650 init/main.c:1222 > do_initcall_level init/main.c:1295 [inline] > do_initcalls init/main.c:1311 [inline] > do_basic_setup init/main.c:1331 [inline] > kernel_init_freeable+0x600/0x684 init/main.c:1531 > kernel_init+0xd/0x1b8 init/main.c:1420 > ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:296 > > -> #0 (brd_devices_mutex){+.+.}-{3:3}: > check_prev_add kernel/locking/lockdep.c:2866 [inline] > check_prevs_add kernel/locking/lockdep.c:2991 [inline] > validate_chain kernel/locking/lockdep.c:3606 [inline] > __lock_acquire+0x2ca6/0x5c00 kernel/locking/lockdep.c:4830 > lock_acquire kernel/locking/lockdep.c:5435 [inline] > lock_acquire+0x2a3/0x8c0 kernel/locking/lockdep.c:5400 > __mutex_lock_common kernel/locking/mutex.c:956 [inline] > __mutex_lock+0x134/0x1110 kernel/locking/mutex.c:1103 > brd_probe+0x31/0x250 drivers/block/brd.c:434 > request_gendisk_module block/genhd.c:979 [inline] > get_gendisk+0x4c3/0x6a0 block/genhd.c:1029 > bdev_get_gendisk fs/block_dev.c:1094 [inline] > __blkdev_get+0x344/0x1870 fs/block_dev.c:1455 > blkdev_get+0xd1/0x240 fs/block_dev.c:1634 > blkdev_open+0x21d/0x2b0 fs/block_dev.c:1751 > do_dentry_open+0x4b9/0x11b0 fs/open.c:817 > do_open fs/namei.c:3252 [inline] > path_openat+0x1b9a/0x2730 fs/namei.c:3369 > do_filp_open+0x17e/0x3c0 fs/namei.c:3396 > do_sys_openat2+0x16d/0x420 fs/open.c:1168 > do_sys_open fs/open.c:1184 [inline] > __do_sys_openat fs/open.c:1200 [inline] > __se_sys_openat fs/open.c:1195 [inline] > __x64_sys_openat+0x13f/0x1f0 fs/open.c:1195 > do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46 > entry_SYSCALL_64_after_hwframe+0x44/0xa9 > > other info that might help us debug this: > > Chain exists of: > brd_devices_mutex --> mtd_table_mutex --> major_names_lock > > Possible unsafe locking scenario: > > CPU0 CPU1 > ---- ---- > lock(major_names_lock); > lock(mtd_table_mutex); > lock(major_names_lock); > lock(brd_devices_mutex); > > *** DEADLOCK *** > > 1 lock held by syz-executor541/8491: > #0: ffffffff8bac3508 (major_names_lock){+.+.}-{3:3}, at: request_gendisk_module block/genhd.c:976 [inline] > #0: ffffffff8bac3508 (major_names_lock){+.+.}-{3:3}, at: get_gendisk+0x3c8/0x6a0 block/genhd.c:1029 > > stack backtrace: > CPU: 0 PID: 8491 Comm: syz-executor541 Not tainted 5.10.0-rc3-next-20201116-syzkaller #0 > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 > Call Trace: > __dump_stack lib/dump_stack.c:79 [inline] > dump_stack+0x107/0x163 lib/dump_stack.c:120 > check_noncircular+0x25f/0x2e0 kernel/locking/lockdep.c:2115 > check_prev_add kernel/locking/lockdep.c:2866 [inline] > check_prevs_add kernel/locking/lockdep.c:2991 [inline] > validate_chain kernel/locking/lockdep.c:3606 [inline] > __lock_acquire+0x2ca6/0x5c00 kernel/locking/lockdep.c:4830 > lock_acquire kernel/locking/lockdep.c:5435 [inline] > lock_acquire+0x2a3/0x8c0 kernel/locking/lockdep.c:5400 > __mutex_lock_common kernel/locking/mutex.c:956 [inline] > __mutex_lock+0x134/0x1110 kernel/locking/mutex.c:1103 > brd_probe+0x31/0x250 drivers/block/brd.c:434 > request_gendisk_module block/genhd.c:979 [inline] > get_gendisk+0x4c3/0x6a0 block/genhd.c:1029 > bdev_get_gendisk fs/block_dev.c:1094 [inline] > __blkdev_get+0x344/0x1870 fs/block_dev.c:1455 > blkdev_get+0xd1/0x240 fs/block_dev.c:1634 > blkdev_open+0x21d/0x2b0 fs/block_dev.c:1751 > do_dentry_open+0x4b9/0x11b0 fs/open.c:817 > do_open fs/namei.c:3252 [inline] > path_openat+0x1b9a/0x2730 fs/namei.c:3369 > do_filp_open+0x17e/0x3c0 fs/namei.c:3396 > do_sys_openat2+0x16d/0x420 fs/open.c:1168 > do_sys_open fs/open.c:1184 [inline] > __do_sys_openat fs/open.c:1200 [inline] > __se_sys_openat fs/open.c:1195 [inline] > __x64_sys_openat+0x13f/0x1f0 fs/open.c:1195 > do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46 > entry_SYSCALL_64_after_hwframe+0x44/0xa9 > RIP: 0033:0x445ec9 > Code: e8 fc b8 02 00 48 83 c4 18 c3 0f 1f 80 00 00 00 00 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 0b 12 fc ff c3 66 2e 0f 1f 84 00 00 00 00 > RSP: 002b:00007f6bca748d98 EFLAGS: 00000246 ORIG_RAX: 0000000000000101 > RAX: ffffffffffffffda RBX: 00000000006ddc38 RCX: 0000000000445ec9 > RDX: 0000000000000000 RSI: 0000000020002040 RDI: 00000000ffffff9c > > > --- > This report 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 issue. See: > https://goo.gl/tpsmEJ#status for how to communicate with syzbot. > syzbot can test patches for this issue, for details see: > https://goo.gl/tpsmEJ#testing-patches ---end quoted text---
