Re: [PATCH] io_uring: only restore req->work for req that needs do completion

[Jens Axboe <axboe@kernel.dk>]

On 4/18/20 8:06 PM, Xiaoguang Wang wrote:
> When testing io_uring IORING_FEAT_FAST_POLL feature, I got below panic:
> BUG: kernel NULL pointer dereference, address: 0000000000000030
> PGD 0 P4D 0
> Oops: 0000 [#1] SMP PTI
> CPU: 5 PID: 2154 Comm: io_uring_echo_s Not tainted 5.6.0+ #359
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
> BIOS rel-1.11.1-0-g0551a4be2c-prebuilt.qemu-project.org 04/01/2014
> RIP: 0010:io_wq_submit_work+0xf/0xa0
> Code: ff ff ff be 02 00 00 00 e8 ae c9 19 00 e9 58 ff ff ff 66 0f 1f
> 84 00 00 00 00 00 0f 1f 44 00 00 41 54 49 89 fc 55 53 48 8b 2f <8b>
> 45 30 48 8d 9d 48 ff ff ff 25 01 01 00 00 83 f8 01 75 07 eb 2a
> RSP: 0018:ffffbef543e93d58 EFLAGS: 00010286
> RAX: ffffffff84364f50 RBX: ffffa3eb50f046b8 RCX: 0000000000000000
> RDX: ffffa3eb0efc1840 RSI: 0000000000000006 RDI: ffffa3eb50f046b8
> RBP: 0000000000000000 R08: 00000000fffd070d R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000000 R12: ffffa3eb50f046b8
> R13: ffffa3eb0efc2088 R14: ffffffff85b69be0 R15: ffffa3eb0effa4b8
> FS:  00007fe9f69cc4c0(0000) GS:ffffa3eb5ef40000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000000000000030 CR3: 0000000020410000 CR4: 00000000000006e0
> Call Trace:
>  task_work_run+0x6d/0xa0
>  do_exit+0x39a/0xb80
>  ? get_signal+0xfe/0xbc0
>  do_group_exit+0x47/0xb0
>  get_signal+0x14b/0xbc0
>  ? __x64_sys_io_uring_enter+0x1b7/0x450
>  do_signal+0x2c/0x260
>  ? __x64_sys_io_uring_enter+0x228/0x450
>  exit_to_usermode_loop+0x87/0xf0
>  do_syscall_64+0x209/0x230
>  entry_SYSCALL_64_after_hwframe+0x49/0xb3
> RIP: 0033:0x7fe9f64f8df9
> Code: Bad RIP value.
> 
> task_work_run calls io_wq_submit_work unexpectedly, it's obvious that
> struct callback_head's func member has been changed. After looking into
> codes, I found this issue is still due to the union definition:
>     union {
>         /*
>          * Only commands that never go async can use the below fields,
>          * obviously. Right now only IORING_OP_POLL_ADD uses them, and
>          * async armed poll handlers for regular commands. The latter
>          * restore the work, if needed.
>          */
>         struct {
>             struct callback_head	task_work;
>             struct hlist_node	hash_node;
>             struct async_poll	*apoll;
>         };
>         struct io_wq_work	work;
>     };
> 
> When task_work_run has multiple work to execute, the work that calls
> io_poll_remove_all() will do req->work restore for  non-poll request
> always, but indeed if a non-poll request has been added to a new
> callback_head, subsequent callback will call io_async_task_func() to
> handle this request, that means we should not do the restore work
> for such non-poll request. Meanwhile in io_async_task_func(), we should
> drop submit ref when req has been canceled.
> 
> Fix both issues.

Applied, with io_double_put_req() used.

-- 
Jens Axboe