KCSAN: data-race in blk_mq_dispatch_rq_list / blk_mq_dispatch_rq_list (2)

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 05f22368 x86, kcsan: Enable KCSAN for x86
git tree: https://github.com/google/ktsan.git kcsan
console output: https://syzkaller.appspot.com/x/log.txt?x=17b6b828e00000
kernel config: https://syzkaller.appspot.com/x/.config?x=87d111955f40591f
dashboard link: https://syzkaller.appspot.com/bug?extid=2c308b859c8c103aae53
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
CC: [ax...@kernel.dk linux...@vger.kernel.org
linux-...@vger.kernel.org el...@google.com]

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

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+2c308b...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in blk_mq_dispatch_rq_list / blk_mq_dispatch_rq_list

write to 0xffff8881299a7560 of 8 bytes by task 18646 on cpu 0:
blk_mq_dispatch_rq_list+0x4d9/0xe40 block/blk-mq.c:1298
blk_mq_do_dispatch_sched+0x11d/0x260 block/blk-mq-sched.c:115
blk_mq_sched_dispatch_requests+0x2b4/0x380 block/blk-mq-sched.c:211
__blk_mq_run_hw_queue+0xb7/0x160 block/blk-mq.c:1403
__blk_mq_delay_run_hw_queue+0x31b/0x3a0 block/blk-mq.c:1471
blk_mq_run_hw_queue+0x103/0x1c0 block/blk-mq.c:1508
blk_mq_sched_insert_requests+0x1ca/0x2e0 block/blk-mq-sched.c:444
blk_mq_flush_plug_list+0x572/0x6c0 block/blk-mq.c:1772
blk_flush_plug_list+0x271/0x2a0 block/blk-core.c:1766
blk_finish_plug block/blk-core.c:1783 [inline]
blk_finish_plug+0x60/0x84 block/blk-core.c:1779
do_blockdev_direct_IO+0x48b6/0x78c0 fs/direct-io.c:1355
__blockdev_direct_IO+0x86/0xa0 fs/direct-io.c:1412
ext4_direct_IO_write fs/ext4/inode.c:3742 [inline]
ext4_direct_IO+0x6f5/0xf70 fs/ext4/inode.c:3871
generic_file_direct_write+0x14d/0x2e0 mm/filemap.c:3207

read to 0xffff8881299a7560 of 8 bytes by task 18647 on cpu 1:
blk_mq_dispatch_rq_list+0x4c4/0xe40 block/blk-mq.c:1298
blk_mq_do_dispatch_sched+0x11d/0x260 block/blk-mq-sched.c:115
blk_mq_sched_dispatch_requests+0x2b4/0x380 block/blk-mq-sched.c:211
__blk_mq_run_hw_queue+0xb7/0x160 block/blk-mq.c:1403
__blk_mq_delay_run_hw_queue+0x31b/0x3a0 block/blk-mq.c:1471
blk_mq_run_hw_queue+0x103/0x1c0 block/blk-mq.c:1508
blk_mq_sched_insert_requests+0x1ca/0x2e0 block/blk-mq-sched.c:444
blk_mq_flush_plug_list+0x572/0x6c0 block/blk-mq.c:1772
blk_flush_plug_list+0x271/0x2a0 block/blk-core.c:1766
blk_finish_plug block/blk-core.c:1783 [inline]
blk_finish_plug+0x60/0x84 block/blk-core.c:1779
do_blockdev_direct_IO+0x48b6/0x78c0 fs/direct-io.c:1355
__blockdev_direct_IO+0x86/0xa0 fs/direct-io.c:1412
ext4_direct_IO_write fs/ext4/inode.c:3742 [inline]
ext4_direct_IO+0x6f5/0xf70 fs/ext4/inode.c:3871

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 18647 Comm: syz-executor.2 Not tainted 5.4.0-rc3+ #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.