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Commit 7e6d72c1 authored by Marcelo Tosatti's avatar Marcelo Tosatti Committed by Dave Airlie
Browse files

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: default avatarMarcelo Tosatti <mtosatti@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: default avatarDave Airlie <airlied@redhat.com>
parent 5cef29aa

drivers/video/console/vgacon.c

+12 −4
Original line number Original line Diff line number Diff line
@@ -1124,11 +1124,15 @@ static int vgacon_do_font_op(struct vgastate *state,char *arg,int set,int ch512) 




	if (arg) {

	if (arg) {

		if (set)

		if (set)

			for (i = 0; i < cmapsz; i++)

			for (i = 0; i < cmapsz; i++) {

				vga_writeb(arg[i], charmap + i);

				vga_writeb(arg[i], charmap + i);

				cond_resched();

			}

		else

		else

			for (i = 0; i < cmapsz; i++)

			for (i = 0; i < cmapsz; i++) {

				arg[i] = vga_readb(charmap + i);

				arg[i] = vga_readb(charmap + i);

				cond_resched();

			}





		/*

		/*

		 * In 512-character mode, the character map is not contiguous if

		 * 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;

			charmap += 2 * cmapsz;

			arg += cmapsz;

			arg += cmapsz;

			if (set)

			if (set)

				for (i = 0; i < cmapsz; i++)

				for (i = 0; i < cmapsz; i++) {

					vga_writeb(arg[i], charmap + i);

					vga_writeb(arg[i], charmap + i);

					cond_resched();

				}

			else

			else

				for (i = 0; i < cmapsz; i++)

				for (i = 0; i < cmapsz; i++) {

					arg[i] = vga_readb(charmap + i);

					arg[i] = vga_readb(charmap + i);

					cond_resched();

				}

		}

		}

	}

	}