[syzbot] [block?] WARNING in bd_unlink_disk_holder

[syzbot] [block?] WARNING in bd_unlink_disk_holder

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    b0958b1397fb arm64: mm: validate /dev/mem mmap ranges with..
git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci
console output: https://syzkaller.appspot.com/x/log.txt?x=1018bddd580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=a58b6b4d667e7a61
dashboard link: https://syzkaller.appspot.com/bug?extid=0a8119ab801b078213ea
compiler:       Debian clang version 22.1.8 (1~deb13u4), Debian LLD 22.1.8
userspace arch: arm64
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1418bddd580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/a1caa79f24c0/disk-b0958b13.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/99b068dd4197/vmlinux-b0958b13.xz
kernel image: https://storage.googleapis.com/syzbot-assets/e135f96e545e/Image-b0958b13.gz.xz

AI-generated root cause summary:
In drivers/md/md.c:bind_rdev_to_array(), an rdev is added to mddev->disks and
bd_link_disk_holder() is called to create the holder/slave relationship without
checking its return value. If bd_link_disk_holder() fails (for example,
returning -EINVAL when an array's own block device or partition is imported into
itself, or on memory/sysfs failures), no bd_holder_disk entry is added to
disk->slave_bdevs, yet the device remains bound to the array. When the array is
subsequently stopped via do_md_stop() -> export_array() ->
md_kick_rdev_from_array(), bd_unlink_disk_holder() is called and
bd_find_holder_disk() returns NULL, triggering WARN_ON_ONCE(holder == NULL) at
block/holder.c:147.

full analysis:  https://syzkaller.appspot.com/x/ai_root_cause?x=0a8119ab801b078213ea

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+0a8119ab801b078213ea@syzkaller.appspotmail.com

md: md4 stopped.
------------[ cut here ]------------
WARNING: block/holder.c:147 at bd_find_holder_disk block/holder.c:18 [inline], CPU#0: syz.4.21/5133
WARNING: block/holder.c:147 at bd_unlink_disk_holder+0xd8/0x2d4 block/holder.c:146, CPU#0: syz.4.21/5133
Modules linked in:
CPU: 0 UID: 0 PID: 5133 Comm: syz.4.21 Not tainted syzkaller #0 PREEMPT 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/14/2026
pstate: 83400005 (Nzcv daif +PAN -UAO +TCO +DIT -SSBS BTYPE=--)
pc : bd_unlink_disk_holder+0xd8/0x2d4 block/holder.c:18
lr : bd_find_holder_disk block/holder.c:18 [inline]
lr : bd_unlink_disk_holder+0xd8/0x2d4 block/holder.c:146
sp : ffff800098f877e0
x29: ffff800098f877e0 x28: 1fffe000192c2f06 x27: ffff0000d92043d0
x26: 1fffe00018291306 x25: 1fffe0001b240879 x24: ffff0000d92043c8
x23: dfff800000000000 x22: ffff0000c1489830 x21: ffff0000c1489700
x20: ffff0000d9204000 x19: ffff0000d92043d0 x18: 1fffe000359cf228
x17: 0000000000000003 x16: ffff8000898b7000 x15: ffff80008996b2a0
x14: 00000000005a60a9 x13: 0000000000000001 x12: 0000000000000003
x11: 0000000000000000 x10: 0000000000000001 x9 : 0000000000000000
x8 : 0000000000000000 x7 : ffff8000818fb144 x6 : 0000000000000000
x5 : 0000000000000000 x4 : 0000000000000001 x3 : ffff80008046bc7c
x2 : 0000000000000001 x1 : ffff0000d96b0000 x0 : 0000000000000000
Call trace:
 bd_find_holder_disk block/holder.c:18 [inline] (P)
 bd_unlink_disk_holder+0xd8/0x2d4 block/holder.c:146 (P)
 md_kick_rdev_from_array+0x8c/0x324 drivers/md/md.c:2683
 export_array drivers/md/md.c:2714 [inline]
 do_md_stop+0x708/0xe6c drivers/md/md.c:7252
 md_ioctl+0x14ec/0x23e4 drivers/md/md.c:8462
 blkdev_ioctl+0x574/0x904 block/ioctl.c:798
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl fs/ioctl.c:583 [inline]
 __arm64_sys_ioctl+0x154/0x1cc fs/ioctl.c:583
 __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
 invoke_syscall+0x98/0x244 arch/arm64/kernel/syscall.c:49
 el0_svc_common+0xec/0x23c arch/arm64/kernel/syscall.c:121
 do_el0_svc+0x4c/0x5c arch/arm64/kernel/syscall.c:140
 el0_svc+0x60/0x1d8 arch/arm64/kernel/entry-common.c:796
 el0t_64_sync_handler+0x44/0x104 arch/arm64/kernel/entry-common.c:815
 el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:606
irq event stamp: 2038
hardirqs last  enabled at (2037): [<ffff8000804a3fb4>] vprintk_store+0x924/0xb94 kernel/printk/printk.c:2385
hardirqs last disabled at (2038): [<ffff800086953878>] el1_brk64+0x20/0x54 arch/arm64/kernel/entry-common.c:483
softirqs last  enabled at (1948): [<ffff8000801373b8>] local_bh_enable include/linux/bottom_half.h:33 [inline]
softirqs last  enabled at (1948): [<ffff8000801373b8>] put_cpu_fpsimd_context arch/arm64/kernel/fpsimd.c:251 [inline]
softirqs last  enabled at (1948): [<ffff8000801373b8>] do_sve_acc+0x3ac/0x56c arch/arm64/kernel/fpsimd.c:1333
softirqs last disabled at (1946): [<ffff800080137110>] local_bh_disable include/linux/bottom_half.h:20 [inline]
softirqs last disabled at (1946): [<ffff800080137110>] get_cpu_fpsimd_context arch/arm64/kernel/fpsimd.c:234 [inline]
softirqs last disabled at (1946): [<ffff800080137110>] do_sve_acc+0x104/0x56c arch/arm64/kernel/fpsimd.c:1308
---[ end trace 0000000000000000 ]---


---
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