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, we need to read more data and this used to work prior to commit aaec5a95d59615 ("pipe_read: don't wake up the writer if the pipe is still full"). p9_read_work() does p9_fd_read() -> ... -> anon_pipe_read() which (before the commit above) triggered the unnecessary wakeup. This wakeup calls p9_pollwake() which kicks p9_poll_workfn() -> p9_poll_mux(), p9_poll_mux() will notice EPOLLIN and schedule_work(&m->rq). This no longer happens after the optimization above, change p9_fd_request() to use p9_poll_mux() instead of only checking for EPOLLOUT. Reported-by: syzbot+d1b5dace43896bc386c3@syzkaller.appspotmail.com Tested-by: syzbot+d1b5dace43896bc386c3@syzkaller.appspotmail.com Closes: https://lore.kernel.org/all/68a2de8f.050a0220.e29e5.0097.GAE@google.com/ Link: https://lore.kernel.org/all/67dedd2f.050a0220.31a16b.003f.GAE@google.com/ Co-developed-by: K Prateek Nayak Signed-off-by: K Prateek Nayak Signed-off-by: Oleg Nesterov --- net/9p/trans_fd.c | 9 +-------- 1 file changed, 1 insertion(+), 8 deletions(-) diff --git a/net/9p/trans_fd.c b/net/9p/trans_fd.c index 339ec4e54778..474fe67f72ac 100644 --- a/net/9p/trans_fd.c +++ b/net/9p/trans_fd.c @@ -666,7 +666,6 @@ 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; int err; struct p9_trans_fd *ts = client->trans; struct p9_conn *m = &ts->conn; @@ -686,13 +685,7 @@ 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; } -- 2.25.1.362.g51ebf55