9p: trans_fd/p9_conn_cancel: drop client lock earlier

stable inclusion
from stable-v5.10.156
commit f14858bc77c567e089965962877ee726ffad0556
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I7MCG1

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f14858bc77c567e089965962877ee726ffad0556

--------------------------------

commit 52f1c45d upstream.

syzbot reported a double-lock here and we no longer need this
lock after requests have been moved off to local list:
just drop the lock earlier.

Link: https://lkml.kernel.org/r/20220904064028.1305220-1-asmadeus@codewreck.org
Reported-by: syzbot+50f7e8d06c3768dd97f3@syzkaller.appspotmail.com
Signed-off-by: NDominique Martinet <asmadeus@codewreck.org>
Tested-by: Schspa Shi <schspa@gmail.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Nsanglipeng <sanglipeng1@jd.com>

net/9p/trans_fd.c

@@ -205,6 +205,8 @@ static void p9_conn_cancel(struct p9_conn *m, int err)
 		list_move(&req->req_list, &cancel_list);
 	}
 
+	spin_unlock(&m->client->lock);
+
 	list_for_each_entry_safe(req, rtmp, &cancel_list, req_list) {
 		p9_debug(P9_DEBUG_ERROR, "call back req %p\n", req);
 		list_del(&req->req_list);
@@ -212,7 +214,6 @@ static void p9_conn_cancel(struct p9_conn *m, int err)
 			req->t_err = err;
 		p9_client_cb(m->client, req, REQ_STATUS_ERROR);
 	}
-	spin_unlock(&m->client->lock);
 }
 
 static __poll_t