On 4/19/2020 5:06 AM, 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.
>
> Fixes: b1f573bd15fd ("io_uring: restore req->work when canceling poll request")
> Signed-off-by: Xiaoguang Wang <xiaoguang.wang@xxxxxxxxxxxxxxxxx>
> ---
> fs/io_uring.c | 9 +++++----
> 1 file changed, 5 insertions(+), 4 deletions(-)
>
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index 381d50becd04..b4f89023df1e 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -4200,17 +4200,18 @@ static void io_async_task_func(struct callback_head *cb)
>
> spin_unlock_irq(&ctx->completion_lock);
>
> + /* restore ->work in case we need to retry again */
> + memcpy(&req->work, &apoll->work, sizeof(req->work));
> +
> if (canceled) {
> kfree(apoll);
> io_cqring_ev_posted(ctx);
> req_set_fail_links(req);
> io_put_req(req);
> + io_put_req(req);
Using io_double_put_req() would be even better
> return;
> }
>
> - /* restore ->work in case we need to retry again */
> - memcpy(&req->work, &apoll->work, sizeof(req->work));
> -
> __set_current_state(TASK_RUNNING);
> mutex_lock(&ctx->uring_lock);
> __io_queue_sqe(req, NULL);
> @@ -4369,7 +4370,7 @@ static bool io_poll_remove_one(struct io_kiocb *req)
>
> hash_del(&req->hash_node);
>
> - if (apoll) {
> + if (do_complete && apoll) {
> /*
> * restore ->work because we need to call io_req_work_drop_env.
> */
>
--
Pavel Begunkov
