[moderation] [block?] KCSAN: data-race in __mod_timer / blk_add_timer (13)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 2061f18ad76e Merge tag 'caps-pr-20251204' of git://git.ker..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=12bc7192580000
kernel config: https://syzkaller.appspot.com/x/.config?x=fe265072cbd2f67a
dashboard link: https://syzkaller.appspot.com/bug?extid=b2cfdce5ab94c6187dc4
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
CC: [ax...@kernel.dk linux...@vger.kernel.org linux-...@vger.kernel.org]

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/68ad9eabb708/disk-2061f18a.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/756a6923eb62/vmlinux-2061f18a.xz
kernel image: https://storage.googleapis.com/syzbot-assets/dbf0c80cc61c/bzImage-2061f18a.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+b2cfdc...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in __mod_timer / blk_add_timer

write to 0xffff888101760920 of 8 bytes by task 9042 on cpu 0:
__mod_timer+0x5a1/0x840 kernel/time/timer.c:1126
mod_timer+0x1f/0x30 kernel/time/timer.c:1195
blk_add_timer+0x182/0x1a0 block/blk-timeout.c:164
blk_mq_start_request+0x183/0x3d0 block/blk-mq.c:1374
loop_queue_rq+0x43/0x680 drivers/block/loop.c:1860
__blk_mq_issue_directly block/blk-mq.c:2714 [inline]
blk_mq_request_issue_directly+0x1e9/0x380 block/blk-mq.c:2801
blk_mq_issue_direct+0x19d/0x530 block/blk-mq.c:2822
blk_mq_dispatch_queue_requests+0x1fc/0x350 block/blk-mq.c:2897
blk_mq_flush_plug_list+0x2b6/0x330 block/blk-mq.c:2980
__blk_flush_plug+0x222/0x2a0 block/blk-core.c:1225
blk_finish_plug block/blk-core.c:1252 [inline]
__submit_bio+0x2fc/0x4d0 block/blk-core.c:651
__submit_bio_noacct_mq block/blk-core.c:724 [inline]
submit_bio_noacct_nocheck+0x152/0x5c0 block/blk-core.c:755
submit_bio_noacct+0x746/0x9a0 block/blk-core.c:879
submit_bio+0x2a6/0x2c0 block/blk-core.c:921
submit_bh_wbc+0x2e0/0x320 fs/buffer.c:2824
submit_bh fs/buffer.c:2829 [inline]
__bread_slow fs/buffer.c:1272 [inline]
__bread_gfp+0x15c/0x240 fs/buffer.c:1518
sb_bread include/linux/buffer_head.h:346 [inline]
isofs_fill_super+0x417/0x12b0 fs/isofs/inode.c:632
get_tree_bdev_flags+0x291/0x300 fs/super.c:1699
get_tree_bdev+0x1f/0x30 fs/super.c:1722
isofs_get_tree+0x1c/0x30 fs/isofs/inode.c:1538
vfs_get_tree+0x57/0x1d0 fs/super.c:1759
fc_mount fs/namespace.c:1199 [inline]
do_new_mount_fc fs/namespace.c:3636 [inline]
do_new_mount+0x24d/0x6a0 fs/namespace.c:3712
path_mount+0x4ab/0xb80 fs/namespace.c:4022
do_mount fs/namespace.c:4035 [inline]
__do_sys_mount fs/namespace.c:4224 [inline]
__se_sys_mount+0x28c/0x2e0 fs/namespace.c:4201
__x64_sys_mount+0x67/0x80 fs/namespace.c:4201
x64_sys_call+0x2cca/0x3000 arch/x86/include/generated/asm/syscalls_64.h:166
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xd8/0x2a0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff888101760920 of 8 bytes by task 3665 on cpu 1:
blk_add_timer+0x115/0x1a0 block/blk-timeout.c:-1
blk_mq_start_request+0x183/0x3d0 block/blk-mq.c:1374
loop_queue_rq+0x43/0x680 drivers/block/loop.c:1860
__blk_mq_issue_directly block/blk-mq.c:2714 [inline]
blk_mq_request_issue_directly+0x1e9/0x380 block/blk-mq.c:2801
blk_mq_issue_direct+0x19d/0x530 block/blk-mq.c:2822
blk_mq_dispatch_queue_requests+0x1fc/0x350 block/blk-mq.c:2897
blk_mq_flush_plug_list+0x2b6/0x330 block/blk-mq.c:2980
__blk_flush_plug+0x222/0x2a0 block/blk-core.c:1225
blk_finish_plug+0x48/0x70 block/blk-core.c:1252
read_pages+0x401/0x480 mm/readahead.c:176
page_cache_ra_unbounded+0x34e/0x450 mm/readahead.c:302
do_page_cache_ra mm/readahead.c:332 [inline]
force_page_cache_ra mm/readahead.c:361 [inline]
page_cache_sync_ra+0x26e/0x6a0 mm/readahead.c:579
filemap_get_pages+0x2d0/0x11b0 mm/filemap.c:2683
filemap_read+0x231/0xa00 mm/filemap.c:2793
blkdev_read_iter+0x22d/0x2e0 block/fops.c:860
new_sync_read fs/read_write.c:491 [inline]
vfs_read+0x64c/0x770 fs/read_write.c:572
ksys_read+0xda/0x1a0 fs/read_write.c:715
__do_sys_read fs/read_write.c:724 [inline]
__se_sys_read fs/read_write.c:722 [inline]
__x64_sys_read+0x40/0x50 fs/read_write.c:722
x64_sys_call+0x2889/0x3000 arch/x86/include/generated/asm/syscalls_64.h:1
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xd8/0x2a0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x00000000ffffb9d3 -> 0x00000000ffffbdbd

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 3665 Comm: udevd Not tainted syzkaller #0 PREEMPT(voluntary)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
==================================================================


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