This is a note to let you know that I've just added the patch titled
vgacon.c: add cond reschedule points in vgacon_do_font_op
to the 3.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
vgacon.c-add-cond-reschedule-points-in-vgacon_do_font_op.patch
and it can be found in the queue-3.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <[email protected]> know about it.
>From 809feb1735e5f4210ba455108ca91cb55b7b8610 Mon Sep 17 00:00:00 2001
From: Marcelo Tosatti <[email protected]>
Date: Thu, 20 Jun 2013 18:05:56 -0300
Subject: vgacon.c: add cond reschedule points in vgacon_do_font_op
From: Marcelo Tosatti <[email protected]>
commit 7e6d72c15ff4cc0c27573901bb05f9eddbd71ed4 upstream.
Booting a 64-vcpu KVM guest, with CONFIG_PREEMPT_VOLUNTARY,
can result in a soft lockup:
BUG: soft lockup - CPU#41 stuck for 67s! [setfont:1505]
RIP: 0010:[<ffffffff812c48da>]
[<ffffffff812c48da>] vgacon_do_font_op.clone.0+0x1ba/0x550
This is due to the 8192 (cmapsz) IO operations taking longer than expected
due to lock contention in QEMU.
Add conditional resched points in between writes allowing other tasks to
execute.
Signed-off-by: Marcelo Tosatti <[email protected]>
Signed-off-by: Dave Airlie <[email protected]>
[bwh: Backported to 3.2: add #include <linux/sched.h>, already present
upstream]
Signed-off-by: Ben Hutchings <[email protected]>
Cc: Qiang Huang <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
drivers/video/console/vgacon.c | 17 +++++++++++++----
1 file changed, 13 insertions(+), 4 deletions(-)
--- a/drivers/video/console/vgacon.c
+++ b/drivers/video/console/vgacon.c
@@ -42,6 +42,7 @@
#include <linux/kd.h>
#include <linux/slab.h>
#include <linux/vt_kern.h>
+#include <linux/sched.h>
#include <linux/selection.h>
#include <linux/spinlock.h>
#include <linux/ioport.h>
@@ -1124,11 +1125,15 @@ static int vgacon_do_font_op(struct vgas
if (arg) {
if (set)
- for (i = 0; i < cmapsz; i++)
+ for (i = 0; i < cmapsz; i++) {
vga_writeb(arg[i], charmap + i);
+ cond_resched();
+ }
else
- for (i = 0; i < cmapsz; i++)
+ for (i = 0; i < cmapsz; i++) {
arg[i] = vga_readb(charmap + i);
+ cond_resched();
+ }
/*
* In 512-character mode, the character map is not contiguous if
@@ -1139,11 +1144,15 @@ static int vgacon_do_font_op(struct vgas
charmap += 2 * cmapsz;
arg += cmapsz;
if (set)
- for (i = 0; i < cmapsz; i++)
+ for (i = 0; i < cmapsz; i++) {
vga_writeb(arg[i], charmap + i);
+ cond_resched();
+ }
else
- for (i = 0; i < cmapsz; i++)
+ for (i = 0; i < cmapsz; i++) {
arg[i] = vga_readb(charmap + i);
+ cond_resched();
+ }
}
}
Patches currently in stable-queue which might be from [email protected] are
queue-3.4/vgacon.c-add-cond-reschedule-points-in-vgacon_do_font_op.patch
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