KCSAN: data-race in blk_mq_do_dispatch_sched / blk_mq_request_bypass_insert

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 8100a580 Merge tag 'x86-urgent-2020-12-06' of git://git.ke..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=10486813500000
kernel config: https://syzkaller.appspot.com/x/.config?x=4e0bdb085ef78711
dashboard link: https://syzkaller.appspot.com/bug?extid=cbd503fe55400f0ef6f1
compiler: clang version 12.0.0 (https://github.com/llvm/llvm-project.git 913f6005669cfb590c99865a90bc51ed0983d09d)
CC: [ax...@kernel.dk linux...@vger.kernel.org linux-...@vger.kernel.org]

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

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+cbd503...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in blk_mq_do_dispatch_sched / blk_mq_request_bypass_insert

write to 0xffff888102d3a810 of 8 bytes by task 2980 on cpu 1:
__list_add include/linux/list.h:70 [inline]
list_add include/linux/list.h:86 [inline]
blk_mq_request_bypass_insert+0x6a/0x130 block/blk-mq.c:1857
blk_mq_sched_insert_request+0x12c/0x280 block/blk-mq-sched.c:450
blk_mq_requeue_work+0x37b/0x490 block/blk-mq.c:813
process_one_work+0x3e1/0x950 kernel/workqueue.c:2272
worker_thread+0x635/0xb90 kernel/workqueue.c:2418
kthread+0x1fd/0x220 kernel/kthread.c:292
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:296

read to 0xffff888102d3a810 of 8 bytes by task 15157 on cpu 0:
list_empty_careful include/linux/list.h:319 [inline]
__blk_mq_do_dispatch_sched block/blk-mq-sched.c:138 [inline]
blk_mq_do_dispatch_sched+0x17c/0x610 block/blk-mq-sched.c:199
__blk_mq_sched_dispatch_requests+0x1fd/0x2a0 block/blk-mq-sched.c:310
blk_mq_sched_dispatch_requests+0x8f/0xf0 block/blk-mq-sched.c:341
__blk_mq_run_hw_queue+0xee/0x1c0 block/blk-mq.c:1532
__blk_mq_delay_run_hw_queue+0x17d/0x330 block/blk-mq.c:1609
blk_mq_run_hw_queue+0x231/0x260 block/blk-mq.c:1662
blk_mq_sched_insert_requests+0x144/0x210 block/blk-mq-sched.c:501
blk_mq_flush_plug_list+0x2f5/0x400 block/blk-mq.c:1932
blk_flush_plug_list+0x235/0x260 block/blk-core.c:1760
blk_finish_plug+0x44/0x60 block/blk-core.c:1777
ext4_writepages+0x18ad/0x1e30 fs/ext4/inode.c:2843
do_writepages+0x7b/0x150 mm/page-writeback.c:2352
__filemap_fdatawrite_range+0x19d/0x1d0 mm/filemap.c:422
file_write_and_wait_range+0x9f/0x120 mm/filemap.c:761
ext4_sync_file+0x105/0x6c0 fs/ext4/fsync.c:151
vfs_fsync_range+0x107/0x120 fs/sync.c:200
generic_write_sync include/linux/fs.h:2739 [inline]
ext4_buffered_write_iter+0x384/0x3d0 fs/ext4/file.c:278
ext4_file_write_iter+0x45e/0x1090 fs/ext4/file.c:503
call_write_iter include/linux/fs.h:1903 [inline]
do_iter_readv_writev+0x2cb/0x360 fs/read_write.c:740
do_iter_write+0x112/0x4b0 fs/read_write.c:866
vfs_iter_write+0x4c/0x70 fs/read_write.c:907
iter_file_splice_write+0x42a/0x780 fs/splice.c:686
do_splice_from fs/splice.c:764 [inline]
direct_splice_actor+0x80/0xa0 fs/splice.c:933
splice_direct_to_actor+0x345/0x650 fs/splice.c:888
do_splice_direct+0xf5/0x170 fs/splice.c:976
do_sendfile+0x5db/0xca0 fs/read_write.c:1257
__do_sys_sendfile64 fs/read_write.c:1318 [inline]
__se_sys_sendfile64 fs/read_write.c:1304 [inline]
__x64_sys_sendfile64+0xf2/0x130 fs/read_write.c:1304
do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 15157 Comm: syz-executor.2 Not tainted 5.10.0-rc6-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
==================================================================


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[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.