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vgacon.c: add cond reschedule points in vgacon_do_font_op

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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 <mtosatti@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: Dave Airlie <airlied@redhat.com>
This commit is contained in:
Marcelo Tosatti 2013-06-20 18:05:56 -03:00 committed by Dave Airlie
parent 5cef29aa52
commit 7e6d72c15f
1 changed files with 12 additions and 4 deletions
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16
drivers/video/console/vgacon.c
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@ -1124,11 +1124,15 @@ static int vgacon_do_font_op(struct vgastate *state,char *arg,int set,int ch512)
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 +1143,15 @@ static int vgacon_do_font_op(struct vgastate *state,char *arg,int set,int ch512)
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();
}
}
}