um: Fix uml_mconsole stop/go

stable inclusion
from stable-v5.10.110
commit 272c74323dcc5b65e6e20f89c9283b3696ed36a7
bugzilla: https://gitee.com/openeuler/kernel/issues/I574AL

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=272c74323dcc5b65e6e20f89c9283b3696ed36a7

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

commit 1a3a6a2a upstream.

Moving to an EPOLL based IRQ controller broke uml_mconsole stop/go
commands. This fixes it and restores stop/go functionality.

Fixes: ff6a1798 ("Epoll based IRQ controller")
Signed-off-by: NAnton Ivanov <anton.ivanov@cambridgegreys.com>
Signed-off-by: NRichard Weinberger <richard@nod.at>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NYu Liao <liaoyu15@huawei.com>
Reviewed-by: NWei Li <liwei391@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

arch/um/drivers/mconsole_kern.c

@@ -223,7 +223,7 @@ void mconsole_go(struct mc_request *req)
 
 void mconsole_stop(struct mc_request *req)
 {
-	deactivate_fd(req->originating_fd, MCONSOLE_IRQ);
+	block_signals();
 	os_set_fd_block(req->originating_fd, 1);
 	mconsole_reply(req, "stopped", 0, 0);
 	for (;;) {
@@ -246,6 +246,7 @@ void mconsole_stop(struct mc_request *req)
 	}
 	os_set_fd_block(req->originating_fd, 0);
 	mconsole_reply(req, "", 0, 0);
+	unblock_signals();
 }
 
 static DEFINE_SPINLOCK(mc_devices_lock);