The patch below does not apply to the 3.10-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.
thanks, greg k-h ------------------ original commit in Linus's tree ------------------ >From 7e6d72c15ff4cc0c27573901bb05f9eddbd71ed4 Mon Sep 17 00:00:00 2001 From: Marcelo Tosatti <[email protected]> Date: Thu, 20 Jun 2013 18:05:56 -0300 Subject: [PATCH] vgacon.c: add cond reschedule points in vgacon_do_font_op 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]> Cc: [email protected] Signed-off-by: Dave Airlie <[email protected]> diff --git a/drivers/video/console/vgacon.c b/drivers/video/console/vgacon.c index 5855d17d..0dd6d962 100644 --- a/drivers/video/console/vgacon.c +++ b/drivers/video/console/vgacon.c @@ -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(); + } } } -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
