[syzbot] [raid?] BUG: unable to handle kernel paging request in remove_spares

[syzbot] [raid?] BUG: unable to handle kernel paging request in remove_spares

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    6628e7d4c6b2 Linux 7.4-rc1
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=15e6892d580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=a58b6b4d667e7a61
dashboard link: https://syzkaller.appspot.com/bug?extid=a53c2918175b36cfd601
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=167b4359580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/f7244eb9fc82/disk-6628e7d4.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/7915cff348a4/vmlinux-6628e7d4.xz
kernel image: https://storage.googleapis.com/syzbot-assets/e1ce9287de30/Image-6628e7d4.gz.xz

AI-generated root cause summary:
In the MD (Multiple Devices / RAID) subsystem, md_start_sync is scheduled as a
work item on the md_misc workqueue to initiate resynchronization or manage spare
devices. For read-only arrays (!md_is_rdwr(mddev)), md_start_sync executes
remove_and_add_spares(), which invokes remove_spares(). However, md_start_sync
fails to verify whether the array's personality (mddev->pers) is still valid
before calling into personality operations, and array stop/detach sequences do
not ensure that mddev->sync_work is completely halted or prevented from running
after mddev->pers is cleared. When remove_spares() executes with mddev->pers ==
NULL, it attempts to invoke mddev->pers->hot_remove_disk (located at offset
0x50), triggering a NULL pointer dereference crash.

full analysis:  https://syzkaller.appspot.com/x/ai_root_cause?x=a53c2918175b36cfd601

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+a53c2918175b36cfd601@syzkaller.appspotmail.com

Unable to handle kernel paging request at virtual address dfff80000000000a
KASAN: null-ptr-deref in range [0x0000000000000050-0x0000000000000057]
Mem abort info:
  ESR = 0x0000000096000005
  EC = 0x25: DABT (current EL), IL = 32 bits
  SET = 0, FnV = 0
  EA = 0, S1PTW = 0
  FSC = 0x05: level 1 translation fault
Data abort info:
  ISV = 0, ISS = 0x00000005, ISS2 = 0x00000000
  CM = 0, WnR = 0, TnD = 0, TagAccess = 0
  GCS = 0, Overlay = 0, DirtyBit = 0
[dfff80000000000a] address between user and kernel address ranges
Internal error: Oops: 0000000096000005 [#1]  SMP
Modules linked in:
CPU: 1 UID: 0 PID: 4993 Comm: kworker/1:5 Not tainted syzkaller #0 PREEMPT 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/23/2026
Workqueue: md_misc md_start_sync
pstate: 83400005 (Nzcv daif +PAN -UAO +TCO +DIT -SSBS BTYPE=--)
pc : remove_spares+0x100/0x3c8 drivers/md/md.c:10182
lr : remove_spares+0xe0/0x3c8 drivers/md/md.c:10181
sp : ffff800097277900
x29: ffff8000972779a0 x28: ffff0000f4c1c070 x27: 1fffe0001e98380c
x26: dfff800000000000 x25: ffff700012e4ef24 x24: 0000000000000050
x23: 0000000000000000 x22: ffff0000f4c1d108 x21: 0000000000000000
x20: ffff0000f4c1c058 x19: ffff0000f4c1c060 x18: 00000000ffffffff
x17: ffff80012364b000 x16: ffff80008f920000 x15: ffff80008b586000
x14: 00000000001b18f8 x13: 0000000000000001 x12: 0000000000000000
x11: 0000000000000000 x10: ffff60001e983a48 x9 : 0000000000000000
x8 : 000000000000000a x7 : 0000000000000000 x6 : 0000000000000000
x5 : 0000000000000001 x4 : 0000000000000008 x3 : ffff8000841063ac
x2 : 0000000000000000 x1 : ffff0000c4d55880 x0 : 0000000000000001
Call trace:
 remove_spares+0x100/0x3c8 drivers/md/md.c:10182 (P)
 remove_and_add_spares+0xf4/0x580 drivers/md/md.c:10207
 md_start_sync+0x1f8/0xc80 drivers/md/md.c:10323
 process_one_work kernel/workqueue.c:3495 [inline]
 process_scheduled_works+0x91c/0x1250 kernel/workqueue.c:3578
 worker_thread+0x798/0xbd0 kernel/workqueue.c:3659
 kthread+0x304/0x3d4 kernel/kthread.c:436
 ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:854
Code: 972be018 f9400268 91014118 d343ff08 (387a6908) 
---[ end trace 0000000000000000 ]---
----------------
Code disassembly (best guess):
   0:	972be018 	bl	0xfffffffffcaf8060
   4:	f9400268 	ldr	x8, [x19]
   8:	91014118 	add	x24, x8, #0x50
   c:	d343ff08 	lsr	x8, x24, #3
* 10:	387a6908 	ldrb	w8, [x8, x26] <-- trapping instruction


---
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