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/openbmc/linux/lib/
H A Dsbitmap.c9f8b93a7 Mon Oct 25 11:45:01 CDT 2021 Jens Axboe <axboe@kernel.dk> sbitmap: silence data race warning

KCSAN complaints about the sbitmap hint update:

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

write to 0xffffe8ffffd145b8 of 4 bytes by interrupt on cpu 1:
sbitmap_queue_clear+0xca/0xf0 lib/sbitmap.c:606
blk_mq_put_tag+0x82/0x90
__blk_mq_free_request+0x114/0x180 block/blk-mq.c:507
blk_mq_free_request+0x2c8/0x340 block/blk-mq.c:541
__blk_mq_end_request+0x214/0x230 block/blk-mq.c:565
blk_mq_end_request+0x37/0x50 block/blk-mq.c:574
lo_complete_rq+0xca/0x170 drivers/block/loop.c:541
blk_complete_reqs block/blk-mq.c:584 [inline]
blk_done_softirq+0x69/0x90 block/blk-mq.c:589
__do_softirq+0x12c/0x26e kernel/softirq.c:558
run_ksoftirqd+0x13/0x20 kernel/softirq.c:920
smpboot_thread_fn+0x22f/0x330 kernel/smpboot.c:164
kthread+0x262/0x280 kernel/kthread.c:319
ret_from_fork+0x1f/0x30

write to 0xffffe8ffffd145b8 of 4 bytes by interrupt on cpu 0:
sbitmap_queue_clear+0xca/0xf0 lib/sbitmap.c:606
blk_mq_put_tag+0x82/0x90
__blk_mq_free_request+0x114/0x180 block/blk-mq.c:507
blk_mq_free_request+0x2c8/0x340 block/blk-mq.c:541
__blk_mq_end_request+0x214/0x230 block/blk-mq.c:565
blk_mq_end_request+0x37/0x50 block/blk-mq.c:574
lo_complete_rq+0xca/0x170 drivers/block/loop.c:541
blk_complete_reqs block/blk-mq.c:584 [inline]
blk_done_softirq+0x69/0x90 block/blk-mq.c:589
__do_softirq+0x12c/0x26e kernel/softirq.c:558
run_ksoftirqd+0x13/0x20 kernel/softirq.c:920
smpboot_thread_fn+0x22f/0x330 kernel/smpboot.c:164
kthread+0x262/0x280 kernel/kthread.c:319
ret_from_fork+0x1f/0x30

value changed: 0x00000035 -> 0x00000044

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 10 Comm: ksoftirqd/0 Not tainted 5.15.0-rc6-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
==================================================================

which is a data race, but not an important one. This is just updating the
percpu alloc hint, and the reader of that hint doesn't ever require it to
be valid.

Just annotate it with data_race() to silence this one.

Reported-by: syzbot+4f8bfd804b4a1f95b8f6@syzkaller.appspotmail.com
Acked-by: Marco Elver <elver@google.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>