3.2.49-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Marcelo Tosatti <mtosatti@xxxxxxxxxx> 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 <mtosatti@xxxxxxxxxx> Signed-off-by: Dave Airlie <airlied@xxxxxxxxxx> [bwh: Backported to 3.2: add #include <linux/sched.h>, already present upstream] Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx> --- drivers/video/console/vgacon.c | 16 ++++++++++++---- 1 file changed, 12 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(); + } } } -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html