Message-ID: <00000000000053abd705b44afb9b@google.com>
Date:   Tue, 17 Nov 2020 02:30:20 -0800
From:   syzbot <syzbot+fd01c5d29a476390728d@...kaller.appspotmail.com>
To:     axboe@...nel.dk, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com
Subject: possible deadlock in brd_probe

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@...kaller.appspotmail.com

======================================================
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


---
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