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
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;
}
