> On 03/28, K Prateek Nayak wrote:
>>
>> --- a/net/9p/trans_fd.c
>> +++ b/net/9p/trans_fd.c
>> @@ -687,7 +687,13 @@ static int p9_fd_request(struct p9_client *client, struct p9_req_t *req)
>> else
>> n = p9_fd_poll(m->client, NULL, NULL);
>> - if (n & EPOLLOUT && !test_and_set_bit(Wworksched, &m->wsched))
>> + /* Failed to send request */
>> + if (!(n & EPOLLOUT)) {
>> + p9_conn_cancel(m, -EIO);
>
> Thanks a lot Prateek!
>
> Can't really the changes in net/9p, but I am not sure. !(n & EPOLLOUT)
> means that pipe is full, nothing wrong. We need to kick m->rq in this
> case.
>
> Dominique says:
>
> For me the problem isn't so much that this gets ERESTARTSYS but that it
> nevers gets to read the 7 bytes that are available?
>
> Yes. Of course I do not pretend I fully understand the problem, but it
> seems this is because p9_read_work() doesn't set Rworksched and doesn't
> do schedule_work(&m->rq) if list_empty(&m->req_list).
>
> However, if the pipe is full, before the commit aaec5a95d59615523db0
> ("pipe_read: don't wake up the writer if the pipe is still full"),
> p9_read_work() -> p9_fd_read() -> kernel_read(ts->rd) triggered the
> unnecessary wakeup. This wakeup calls p9_pollwake() shich kicks
> p9_poll_workfn() -> p9_poll_mux(), and p9_poll_mux() will notice
> EPOLLIN and schedule_work(&m->rq).
>
> May be the patch below makes more sense?
>
> Oleg.
>
> #syz test: upstream
want either no args or 2 args (repo, branch), got 5
>
> diff --git a/net/9p/trans_fd.c b/net/9p/trans_fd.c
> index 56e62978e502..aa9cd248a243 100644
> --- a/net/9p/trans_fd.c
> +++ b/net/9p/trans_fd.c
> @@ -669,7 +669,6 @@ static void p9_poll_mux(struct p9_conn *m)
>
> static int p9_fd_request(struct p9_client *client, struct p9_req_t *req)
> {
> - __poll_t n;
> struct p9_trans_fd *ts = client->trans;
> struct p9_conn *m = &ts->conn;
>
> @@ -687,13 +686,7 @@ static int p9_fd_request(struct p9_client *client, struct p9_req_t *req)
> list_add_tail(&req->req_list, &m->unsent_req_list);
> spin_unlock(&m->req_lock);
>
> - if (test_and_clear_bit(Wpending, &m->wsched))
> - n = EPOLLOUT;
> - else
> - n = p9_fd_poll(m->client, NULL, NULL);
> -
> - if (n & EPOLLOUT && !test_and_set_bit(Wworksched, &m->wsched))
> - schedule_work(&m->wq);
> + p9_poll_mux(m);
>
> return 0;
> }
>
