From 9f8b93a7df4d8e1e8715fb2a45a893cffad9da0b Mon Sep 17 00:00:00 2001 From: Jens Axboe Date: Mon, 25 Oct 2021 10:45:01 -0600 Subject: [PATCH] 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 Signed-off-by: Jens Axboe --- lib/sbitmap.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/lib/sbitmap.c b/lib/sbitmap.c index c6e2f1f..2709ab8 100644 --- a/lib/sbitmap.c +++ b/lib/sbitmap.c @@ -631,7 +631,7 @@ EXPORT_SYMBOL_GPL(sbitmap_queue_wake_up); static inline void sbitmap_update_cpu_hint(struct sbitmap *sb, int cpu, int tag) { if (likely(!sb->round_robin && tag < sb->depth)) - *per_cpu_ptr(sb->alloc_hint, cpu) = tag; + data_race(*per_cpu_ptr(sb->alloc_hint, cpu) = tag); } void sbitmap_queue_clear_batch(struct sbitmap_queue *sbq, int offset, -- 2.7.4