KCSAN reports a data race between raid1_end_read_request() and
raid1_read_request().
The completion path updates conf->mirrors[disk].head_position in
update_head_pos() without a lock, while the read-balance heuristic reads
the same field locklessly in is_sequential() and choose_best_rdev().
KCSAN report:
=========================
BUG: KCSAN: data-race in raid1_end_read_request / raid1_read_request
write to 0xffff8f0306ba7868 of 8 bytes by interrupt on cpu 9:
raid1_end_read_request+0xb5/0x440
bio_endio+0x3c9/0x3e0
blk_update_request+0x257/0x770
scsi_end_request+0x4d/0x520
scsi_io_completion+0x6f/0x990
scsi_finish_command+0x188/0x280
scsi_complete+0xac/0x160
blk_complete_reqs+0x8e/0xb0
blk_done_softirq+0x1d/0x30
[...]
read to 0xffff8f0306ba7868 of 8 bytes by task 667002 on cpu 11:
raid1_read_request+0x497/0x1a10
raid1_make_request+0xdf/0x1950
md_handle_request+0x2c5/0x700
md_submit_bio+0x126/0x320
__submit_bio+0x2ec/0x3a0
submit_bio_noacct_nocheck+0x572/0x890
[...]
value changed: 0x0000000000000078 -> 0x00000000005fe448
Signed-off-by: Chen Cheng <chencheng@fnnas.com>
Link: https://patch.msgid.link/20260619044114.1208456-1-chencheng@fnnas.com
Signed-off-by: Yu Kuai <yukuai@fygo.io>
601d3c21b2