File 0092-hw-char-serial-Only-retry-if-qemu_c.patch of Package qemu.15022

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File 0092-hw-char-serial-Only-retry-if-qemu_c.patch of Package qemu.15022

From 7d2a39b6b9bbb3a6be3516d93216fb27637728d5 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 eb72191ee7..9936fa20d3 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 =

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File 0092-hw-char-serial-Only-retry-if-qemu_c.patch of Package qemu.15022

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