From 595cfbc5ae5bfaefa29b57a3f4dec04b76e108c5 Mon Sep 17 00:00:00 2001 From: Marcelo Tosatti Date: Thu, 20 Jun 2013 18:05:56 -0300 Subject: [PATCH] vgacon.c: add cond reschedule points in vgacon_do_font_op 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:[] [] 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 Signed-off-by: Dave Airlie [bwh: Backported to 3.2: add #include , already present upstream] Signed-off-by: Ben Hutchings Cc: Qiang Huang Signed-off-by: Greg Kroah-Hartman --- drivers/video/console/vgacon.c | 17 +++++++++++++---- 1 file changed, 13 insertions(+), 4 deletions(-) diff --git a/drivers/video/console/vgacon.c b/drivers/video/console/vgacon.c index 5855d17d19a..9d8feac6763 100644 --- a/drivers/video/console/vgacon.c +++ b/drivers/video/console/vgacon.c @@ -42,6 +42,7 @@ #include #include #include +#include #include #include #include @@ -1124,11 +1125,15 @@ 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 +1144,15 @@ 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(); + } } } -- 2.34.1