[syzbot] [isdn4linux?] KCSAN: data-race in mISDN_ioctl / mISDN_read (4)

Hello,

syzbot found the following issue on:

HEAD commit:    516471569089 Merge tag 'libcrypto-fixes-for-linus' of git:..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=12417dc2580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=b319ff1b6a2797ca
dashboard link: https://syzkaller.appspot.com/bug?extid=c6e7bcea7ffb7ff46acb
compiler:       Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/daca6d82d1e1/disk-51647156.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/3e0d93470f33/vmlinux-51647156.xz
kernel image: https://storage.googleapis.com/syzbot-assets/27efb1907b03/bzImage-51647156.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: [email protected]

==================================================================
BUG: KCSAN: data-race in mISDN_ioctl / mISDN_read

write to 0xffff88812d848280 of 4 bytes by task 10864 on cpu 1:
 misdn_add_timer drivers/isdn/mISDN/timerdev.c:175 [inline]
 mISDN_ioctl+0x2fb/0x550 drivers/isdn/mISDN/timerdev.c:233
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xce/0x140 fs/ioctl.c:583
 __x64_sys_ioctl+0x43/0x50 fs/ioctl.c:583
 x64_sys_call+0x14b0/0x3000 arch/x86/include/generated/asm/syscalls_64.h:17
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xd8/0x2c0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff88812d848280 of 4 bytes by task 10857 on cpu 0:
 mISDN_read+0x1f2/0x470 drivers/isdn/mISDN/timerdev.c:112
 do_loop_readv_writev fs/read_write.c:847 [inline]
 vfs_readv+0x3fb/0x690 fs/read_write.c:1020
 do_readv+0xe7/0x210 fs/read_write.c:1080
 __do_sys_readv fs/read_write.c:1165 [inline]
 __se_sys_readv fs/read_write.c:1162 [inline]
 __x64_sys_readv+0x45/0x50 fs/read_write.c:1162
 x64_sys_call+0x2831/0x3000 arch/x86/include/generated/asm/syscalls_64.h:20
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xd8/0x2c0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x00000000 -> 0x00000001

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 10857 Comm: syz.0.2523 Tainted: G        W           syzkaller #0 PREEMPT(voluntary) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
==================================================================


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