From: Alan Cox <alan@linux.intel.com>
Date: Sat, 19 Jan 2019 21:38:54 +0000 (+0000)
Subject: tty: Fix deadlock in tty output
X-Git-Url: https://git.ndcode.org/public/gitweb.cgi?a=commitdiff_plain;h=d4e2f098fa4160a64e43f9d5efff956481b710a6;p=FUZIX.git

tty: Fix deadlock in tty output

If you had a dumb tty port (or driver) and your write blocked until pre-emption
then we'd sleep expecting a tty wake event even though the tty doesn't provide
one.

Instead if we got told 'soon' we yield when asked to pre-empt.
---

diff --git a/Kernel/tty.c b/Kernel/tty.c
index 6a90fdbd..37405a6b 100644
--- a/Kernel/tty.c
+++ b/Kernel/tty.c
@@ -547,10 +547,14 @@ uint8_t tty_putc_maywait(uint8_t minor, unsigned char c, uint8_t flag)
 					udata.u_error = EAGAIN;
 					return 1;
 				}
-				irq = di();
-				tty_sleeping(minor);
-				psleep(&ttydata[minor]);
-				irqrestore(irq);
+				if (t != TTY_READY_SOON) {
+					irq = di();
+					tty_sleeping(minor);
+					psleep(&ttydata[minor]);
+					irqrestore(irq);
+				} else
+					/* Yield */
+					switchout();
 			}
 		}
 	}