On 30/05/2020 20:29, Jens Axboe wrote:
> 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.
>
There is another thing:
io_submit_sqes()
-> io_close() (let ->flush == NULL)
-> __io_close_finish()
-> filp_close(req->close.put_file, *req->work.files*);
where req->work.files is garbage.
--
Pavel Begunkov
