On Mon, 25 Oct 2021 at 15:36, Jens Axboe <axboe@xxxxxxxxx> wrote: [...] > > 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 > > This is just a per-cpu alloc hint, it's racy by nature. What's the > preferred way to silence these? That was my guess, but couldn't quite say. We started looking at write/write races as more likely to be harmful (vs. just read/write), and are inclined to let syzbot send out more of such reports. Marking intentional ones would be ideal so we'll be left with the unintentional ones. I would probably use WRITE_ONCE(), just to make sure the compiler doesn't play games here; or if the code is entirely tolerant to even the compiler miscompiling things, wrap the thing in data_race(). [ A summary of a bunch of recommendations currently lives here: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/tools/memory-model/Documentation/access-marking.txt ] Thanks, -- Marco
