File 0132-hw-char-serial-Only-retry-if-qemu_c.patch of Package qemu.openSUSE_Leap_42.3_Update

From fff6746c2458ecf1c85f779c1aaa925566bc22e1 Mon Sep 17 00:00:00 2001
From: Sergio Lopez <slp@redhat.com>
Date: Tue, 5 Jun 2018 03:54:55 -0400
Subject: [PATCH] hw/char/serial: Only retry if qemu_chr_fe_write returns 0

Only retry on serial_xmit if qemu_chr_fe_write returns 0, as this is the
only recoverable error.

Retrying with any other scenario, in addition to being a waste of CPU
cycles, can compromise the Guest stability if by the vCPU issuing the
write and the main loop thread are, by chance or explicit pinning,
running on the same pCPU.

Previous discussion:

https://lists.nongnu.org/archive/html/qemu-devel/2018-05/msg06998.html

Signed-off-by: Sergio Lopez <slp@redhat.com>
Message-Id: <1528185295-14199-1-git-send-email-slp@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
(cherry picked from commit 019288bf137183bf3407c9824655b753bfafc99f)
[LY: BSC#1108474]
Signed-off-by: Liang Yan <lyan@suse.com>
---
 hw/char/serial.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/hw/char/serial.c b/hw/char/serial.c
index 03d890ca24..83b4a99323 100644
--- a/hw/char/serial.c
+++ b/hw/char/serial.c
@@ -261,7 +261,7 @@ static void serial_xmit(SerialState *s)
         if (s->mcr & UART_MCR_LOOP) {
             /* in loopback mode, say that we just received a char */
             serial_receive1(s, &s->tsr, 1);
-        } else if (qemu_chr_fe_write(&s->chr, &s->tsr, 1) != 1 &&
+        } else if (qemu_chr_fe_write(&s->chr, &s->tsr, 1) == 0 &&
                    s->tsr_retry < MAX_XMIT_RETRY) {
             assert(s->watch_tag == 0);
             s->watch_tag =