Re: [PATCH] io_uring: restore req->work when canceling poll request

[Xiaoguang Wang <xiaoguang.wang@linux.alibaba.com>]

hi,

> On 4/12/20 12:50 AM, Xiaoguang Wang wrote:
>> When running liburing test case 'accept', I got below warning:
>> RED: Invalid credentials
>> RED: At include/linux/cred.h:285
>> RED: Specified credentials: 00000000d02474a0
>> RED: ->magic=4b, put_addr=000000005b4f46e9
>> RED: ->usage=-1699227648, subscr=-25693
>> RED: ->*uid = { 256,-25693,-25693,65534 }
>> RED: ->*gid = { 0,-1925859360,-1789740800,-1827028688 }
>> RED: ->security is 00000000258c136e
>> eneral protection fault, probably for non-canonical address 0xdead4ead00000000: 0000 [#1] SMP PTI
>> PU: 21 PID: 2037 Comm: accept Not tainted 5.6.0+ #318
>> ardware name: QEMU Standard PC (i440FX + PIIX, 1996),
>> BIOS rel-1.11.1-0-g0551a4be2c-prebuilt.qemu-project.org 04/01/2014
>> IP: 0010:dump_invalid_creds+0x16f/0x184
>> ode: 48 8b 83 88 00 00 00 48 3d ff 0f 00 00 76 29 48 89 c2 81 e2 00 ff ff ff 48
>> 81 fa 00 6b 6b 6b 74 17 5b 48 c7 c7 4b b1 10 8e 5d <8b> 50 04 41 5c 8b 30 41 5d
>> e9 67 e3 04 00 5b 5d 41 5c 41 5d c3 0f
>> SP: 0018:ffffacc1039dfb38 EFLAGS: 00010087
>> AX: dead4ead00000000 RBX: ffff9ba39319c100 RCX: 0000000000000007
>> DX: 0000000000000000 RSI: 0000000000000000 RDI: ffffffff8e10b14b
>> BP: ffffffff8e108476 R08: 0000000000000000 R09: 0000000000000001
>> 10: 0000000000000000 R11: ffffacc1039df9e5 R12: 000000009552b900
>> 13: 000000009319c130 R14: ffff9ba39319c100 R15: 0000000000000246
>> S:  00007f96b2bfc4c0(0000) GS:ffff9ba39f340000(0000) knlGS:0000000000000000
>> S:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>> R2: 0000000000401870 CR3: 00000007db7a4000 CR4: 00000000000006e0
>> all Trace:
>> __invalid_creds+0x48/0x4a
>> __io_req_aux_free+0x2e8/0x3b0
>> ? io_poll_remove_one+0x2a/0x1d0
>> __io_free_req+0x18/0x200
>> io_free_req+0x31/0x350
>> io_poll_remove_one+0x17f/0x1d0
>> io_poll_cancel.isra.80+0x6c/0x80
>> io_async_find_and_cancel+0x111/0x120
>> io_issue_sqe+0x181/0x10e0
>> ? __lock_acquire+0x552/0xae0
>> ? lock_acquire+0x8e/0x310
>> ? fs_reclaim_acquire.part.97+0x5/0x30
>> __io_queue_sqe.part.100+0xc4/0x580
>> ? io_submit_sqes+0x751/0xbd0
>> ? rcu_read_lock_sched_held+0x32/0x40
>> io_submit_sqes+0x9ba/0xbd0
>> ? __x64_sys_io_uring_enter+0x2b2/0x460
>> ? __x64_sys_io_uring_enter+0xaf/0x460
>> ? find_held_lock+0x2d/0x90
>> ? __x64_sys_io_uring_enter+0x111/0x460
>> __x64_sys_io_uring_enter+0x2d7/0x460
>> do_syscall_64+0x5a/0x230
>> entry_SYSCALL_64_after_hwframe+0x49/0xb3
>>
>> After looking into codes, it turns out that this issue is because we didn't
>> restore the req->work, which is changed in io_arm_poll_handler(), req->work
>> is a union with below struct:
>> 	struct {
>> 		struct callback_head	task_work;
>> 		struct hlist_node	hash_node;
>> 		struct async_poll	*apoll;
>> 	};
>> If we forget to restore, members in struct io_wq_work would be invalid,
>> restore the req->work to fix this issue.
> 
> Thanks for debugging this. But how about we just use 'apoll' to see
> if we need to restore or not. Just a slight modification to your patch:
OK, it looks better, thanks. I will post a new version soon.

Regards,
Xiaoguang Wang
> 
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index c0cf57764329..68a678a0056b 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -4318,11 +4318,13 @@ static bool __io_poll_remove_one(struct io_kiocb *req,
>   
>   static bool io_poll_remove_one(struct io_kiocb *req)
>   {
> +	struct async_poll *apoll = NULL;
>   	bool do_complete;
>   
>   	if (req->opcode == IORING_OP_POLL_ADD) {
>   		do_complete = __io_poll_remove_one(req, &req->poll);
>   	} else {
> +		apoll = req->apoll;
>   		/* non-poll requests have submit ref still */
>   		do_complete = __io_poll_remove_one(req, &req->apoll->poll);
>   		if (do_complete)
> @@ -4331,6 +4333,14 @@ static bool io_poll_remove_one(struct io_kiocb *req)
>   
>   	hash_del(&req->hash_node);
>   
> +	if (apoll) {
> +		/*
> +		 * restore ->work because we need to call io_req_work_drop_env.
> +		 */
> +		memcpy(&req->work, &apoll->work, sizeof(req->work));
> +		kfree(apoll);
> +	}
> +
>   	if (do_complete) {
>   		io_cqring_fill_event(req, -ECANCELED);
>   		io_commit_cqring(req->ctx);
>