On 3/23/21 6:34 AM, John Garry wrote: > On 19/03/2021 01:00, Bart Van Assche wrote: >> Multiple users have reported use-after-free complaints similar to the >> following (see also https://lore.kernel.org/linux-block/1545261885.185366.488.camel@xxxxxxx/): >> >> BUG: KASAN: use-after-free in bt_iter+0x86/0xf0 >> Read of size 8 at addr ffff88803b335240 by task fio/21412 >> >> CPU: 0 PID: 21412 Comm: fio Tainted: G W 4.20.0-rc6-dbg+ #3 >> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014 >> Call Trace: >> dump_stack+0x86/0xca >> print_address_description+0x71/0x239 >> kasan_report.cold.5+0x242/0x301 >> __asan_load8+0x54/0x90 >> bt_iter+0x86/0xf0 >> blk_mq_queue_tag_busy_iter+0x373/0x5e0 >> blk_mq_in_flight+0x96/0xb0 >> part_in_flight+0x40/0x140 >> part_round_stats+0x18e/0x370 >> blk_account_io_start+0x3d7/0x670 >> blk_mq_bio_to_request+0x19c/0x3a0 >> blk_mq_make_request+0x7a9/0xcb0 >> generic_make_request+0x41d/0x960 >> submit_bio+0x9b/0x250 >> do_blockdev_direct_IO+0x435c/0x4c70 >> __blockdev_direct_IO+0x79/0x88 >> ext4_direct_IO+0x46c/0xc00 >> generic_file_direct_write+0x119/0x210 >> __generic_file_write_iter+0x11c/0x280 >> ext4_file_write_iter+0x1b8/0x6f0 >> aio_write+0x204/0x310 >> io_submit_one+0x9d3/0xe80 >> __x64_sys_io_submit+0x115/0x340 >> do_syscall_64+0x71/0x210 >> > > Hi Bart, > > Do we have any performance figures to say that the effect is negligible? I ran this through my usual peak testing, it's pretty good at finding any changes in performance related to changes in overhead. The workload is a pretty simple 512b random read, QD 128, using io_uring and polled IO. It seems to cause a slight slowdown for me. Performance before the patch is around 3.23-3.27M IOPS, and after we're at around 3.20-3.22. Looking at perf diff, the most interesting bits seem to be: 2.09% -1.05% [kernel.vmlinux] [k] blk_mq_get_tag 0.48% +0.98% [kernel.vmlinux] [k] __do_sys_io_uring_enter 1.49% +0.85% [kernel.vmlinux] [k] __blk_mq_alloc_request +0.71% [kernel.vmlinux] [k] __blk_mq_free_request which seems to show some shifting around of cost (often happens), but generally up a bit looking at the blk side. So nothing really major here, and I don't think it's something that should getting this fixed. John, I can run your series through the same, let me know. -- Jens Axboe
