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Sat, 30 May 2020 10:29:14 -0700 (PDT) Subject: Re: [PATCH v4 1/2] io_uring: avoid whole io_wq_work copy for requests completed inline From: Jens Axboe To: Xiaoguang Wang , io-uring@vger.kernel.org Cc: asml.silence@gmail.com, joseph.qi@linux.alibaba.com References: <20200530143947.21224-1-xiaoguang.wang@linux.alibaba.com> <8c361177-c0b0-b08c-e0a5-141f7fd948f0@kernel.dk> Message-ID: <27e264ec-2707-495f-3d24-4e9e20b86032@kernel.dk> Date: Sat, 30 May 2020 11:29:13 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.8.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: io-uring-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On 5/30/20 11:14 AM, Jens Axboe wrote: > On 5/30/20 10:44 AM, Jens Axboe wrote: >> On 5/30/20 8:39 AM, Xiaoguang Wang wrote: >>> If requests can be submitted and completed inline, we don't need to >>> initialize whole io_wq_work in io_init_req(), which is an expensive >>> operation, add a new 'REQ_F_WORK_INITIALIZED' to control whether >>> io_wq_work is initialized. >>> >>> I use /dev/nullb0 to evaluate performance improvement in my physical >>> machine: >>> modprobe null_blk nr_devices=1 completion_nsec=0 >>> sudo taskset -c 60 fio -name=fiotest -filename=/dev/nullb0 -iodepth=128 >>> -thread -rw=read -ioengine=io_uring -direct=1 -bs=4k -size=100G -numjobs=1 >>> -time_based -runtime=120 >>> >>> before this patch: >>> Run status group 0 (all jobs): >>> READ: bw=724MiB/s (759MB/s), 724MiB/s-724MiB/s (759MB/s-759MB/s), >>> io=84.8GiB (91.1GB), run=120001-120001msec >>> >>> With this patch: >>> Run status group 0 (all jobs): >>> READ: bw=761MiB/s (798MB/s), 761MiB/s-761MiB/s (798MB/s-798MB/s), >>> io=89.2GiB (95.8GB), run=120001-120001msec >>> >>> About 5% improvement. >> >> There's something funky going on here. I ran the liburing test >> suite on this, and get a lot of left behind workers: >> >> Tests _maybe_ failed: ring-leak open-close open-close file-update file-update accept-reuse accept-reuse poll-v-poll poll-v-poll fadvise fadvise madvise madvise short-read short-read openat2 openat2 probe probe shared-wq shared-wq personality personality eventfd eventfd send_recv send_recv eventfd-ring eventfd-ring across-fork across-fork sq-poll-kthread sq-poll-kthread splice splice lfs-openat lfs-openat lfs-openat-write lfs-openat-write iopoll iopoll d4ae271dfaae-test d4ae271dfaae-test eventfd-disable eventfd-disable write-file write-file buf-rw buf-rw statx statx >> >> and also saw this: >> >> [ 168.208940] ================================================================== >> [ 168.209311] BUG: KASAN: use-after-free in __lock_acquire+0x8bf/0x3000 >> [ 168.209626] Read of size 8 at addr ffff88806801c0d8 by task io_wqe_worker-0/41761 >> [ 168.209987] >> [ 168.210069] CPU: 0 PID: 41761 Comm: io_wqe_worker-0 Not tainted 5.7.0-rc7+ #6318 >> [ 168.210424] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1ubuntu1 04/01/2014 >> [ 168.210857] Call Trace: >> [ 168.210991] dump_stack+0x97/0xe0 >> [ 168.211164] print_address_description.constprop.0+0x1a/0x210 >> [ 168.211446] ? __lock_acquire+0x8bf/0x3000 >> [ 168.211649] __kasan_report.cold+0x20/0x39 >> [ 168.211851] ? __lock_acquire+0x8bf/0x3000 >> [ 168.212051] kasan_report+0x30/0x40 >> [ 168.212226] __lock_acquire+0x8bf/0x3000 >> [ 168.212432] ? ret_from_fork+0x24/0x30 >> [ 168.212623] ? stack_trace_save+0x81/0xa0 >> [ 168.212821] ? lockdep_hardirqs_on+0x270/0x270 >> [ 168.213039] ? save_stack+0x32/0x40 >> [ 168.213212] lock_acquire+0x122/0x570 >> [ 168.213398] ? __close_fd_get_file+0x40/0x150 >> [ 168.213615] ? lock_release+0x3f0/0x3f0 >> [ 168.213814] ? __lock_acquire+0x87e/0x3000 >> [ 168.214016] _raw_spin_lock+0x2c/0x40 >> [ 168.214196] ? __close_fd_get_file+0x40/0x150 >> [ 168.214408] __close_fd_get_file+0x40/0x150 >> [ 168.214618] io_issue_sqe+0x57f/0x22f0 >> [ 168.214803] ? lockdep_hardirqs_on+0x270/0x270 >> [ 168.215019] ? mark_held_locks+0x24/0x90 >> [ 168.215211] ? quarantine_put+0x6f/0x190 >> [ 168.215404] ? io_assign_current_work+0x59/0x80 >> [ 168.215623] ? __ia32_sys_io_uring_setup+0x30/0x30 >> [ 168.215855] ? find_held_lock+0xcb/0x100 >> [ 168.216054] ? io_worker_handle_work+0x289/0x980 >> [ 168.216280] ? lock_downgrade+0x340/0x340 >> [ 168.216476] ? io_wq_submit_work+0x5d/0x140 >> [ 168.216679] ? _raw_spin_unlock_irq+0x24/0x40 >> [ 168.216890] io_wq_submit_work+0x5d/0x140 >> [ 168.217087] io_worker_handle_work+0x30a/0x980 >> [ 168.217305] ? io_wqe_dec_running.isra.0+0x70/0x70 >> [ 168.217537] ? do_raw_spin_lock+0x100/0x180 >> [ 168.217742] ? rwlock_bug.part.0+0x60/0x60 >> [ 168.217943] io_wqe_worker+0x5fd/0x780 >> [ 168.218126] ? lock_downgrade+0x340/0x340 >> [ 168.218323] ? io_worker_handle_work+0x980/0x980 >> [ 168.218546] ? lockdep_hardirqs_on+0x17d/0x270 >> [ 168.218765] ? __kthread_parkme+0xca/0xe0 >> [ 168.218961] ? io_worker_handle_work+0x980/0x980 >> [ 168.219186] kthread+0x1f0/0x220 >> [ 168.219346] ? kthread_create_worker_on_cpu+0xb0/0xb0 >> [ 168.219590] ret_from_fork+0x24/0x30 >> [ 168.219768] >> [ 168.219846] Allocated by task 41758: >> [ 168.220021] save_stack+0x1b/0x40 >> [ 168.220185] __kasan_kmalloc.constprop.0+0xc2/0xd0 >> [ 168.220416] kmem_cache_alloc+0xe0/0x290 >> [ 168.220607] dup_fd+0x4e/0x5a0 >> [ 168.220758] copy_process+0xe35/0x2bf0 >> [ 168.220942] _do_fork+0xd8/0x550 >> [ 168.221102] __do_sys_clone+0xb5/0xe0 >> [ 168.221282] do_syscall_64+0x5e/0xe0 >> [ 168.221457] entry_SYSCALL_64_after_hwframe+0x49/0xb3 >> [ 168.221729] >> [ 168.221848] Freed by task 41759: >> [ 168.222088] save_stack+0x1b/0x40 >> [ 168.222336] __kasan_slab_free+0x12f/0x180 >> [ 168.222632] slab_free_freelist_hook+0x4d/0x120 >> [ 168.222959] kmem_cache_free+0x90/0x2e0 >> [ 168.223239] do_exit+0x5d2/0x12e0 >> [ 168.223482] do_group_exit+0x6f/0x130 >> [ 168.223754] __x64_sys_exit_group+0x28/0x30 >> [ 168.224061] do_syscall_64+0x5e/0xe0 >> [ 168.224326] entry_SYSCALL_64_after_hwframe+0x49/0xb3 >> [ 168.224686] >> >> which indicates that current->files is no longer valid. > > Narrowed it down to the test/open-close test, and in particular where > it closes the ring itself: > > ret = test_close(&ring, ring.ring_fd, 1); > > This seems to be because you do io_req_init_async() after calling > io_issue_sqe(), and the command handler may have set something > else for ->func at that point. Hence we never call the right > handler if the close needs to be deferred, as it needs to for > the io_uring as it has ->flush() defined. > > Why isn't io_req_init_async() just doing: > > static inline void io_req_init_async(struct io_kiocb *req, > void (*func)(struct io_wq_work **)) > { > if (!(req->flags & REQ_F_WORK_INITIALIZED)) { > req->work = (struct io_wq_work){ .func = func }; > req->flags |= REQ_F_WORK_INITIALIZED; > } > } > > ? I guess that won't always work, if the request has been deferred and we're now setting a new work func. So we really want the 'reset to io_wq_submit_work' to only happen if the opcode hasn't already set a private handler. Can you make that change? Also please fix up missing braces. The cases of: if (something) { line 1 line 2 } else line 3 should always includes braces, if one clause has it. A v5 with those two things would be ready to commit. -- Jens Axboe