PATCH: Crash while suspending on FreeBSD/amd64 8.1-RC2

[Yamagi Burmeister]

Okay, with the help of a friend of mine I managed to track this down.

> (kgdb) bt
> #0  doadump () at pcpu.h:223
> #1  0xffffffff8020dfe9 in boot (howto=260) at
> /usr/src/sys/kern/kern_shutdown.c:416
> #2  0xffffffff8020e41c in panic (fmt=0xffffffff8044ebbb "%s")
>    at /usr/src/sys/kern/kern_shutdown.c:590
> #3  0xffffffff80408bc8 in trap_fatal (frame=0xffffff0004a4e000,
> eva=Variable "eva" is not available.
> )
>    at /usr/src/sys/amd64/amd64/trap.c:777
> #4  0xffffffff80408f94 in trap_pfault (frame=0xffffff803da285e0,
> usermode=0)
>    at /usr/src/sys/amd64/amd64/trap.c:693
> #5  0xffffffff804097da in trap (frame=0xffffff803da285e0)
>    at /usr/src/sys/amd64/amd64/trap.c:451
> #6  0xffffffff803ef543 in calltrap () at
> /usr/src/sys/amd64/amd64/exception.S:223
> #7  0xffffffff80406f16 in bcopy () at
> /usr/src/sys/amd64/amd64/support.S:124
> #8  0xffffffff80745fb7 in vesa_bios_save_restore (code=1,
> p=0xffffff80002a6004,
>    size=4928) at /usr/src/sys/modules/vesa/../../dev/fb/vesa.c:551
> #9  0xffffffff80746059 in vesa_save_state (adp=Variable "adp" is not
> available.
> )
>    at /usr/src/sys/modules/vesa/../../dev/fb/vesa.c:1429
> #10 0xffffffff80424144 in vga_suspend (dev=0xffffff0001632a00)
>    at /usr/src/sys/isa/vga_isa.c:81
> #11 0xffffffff804241d7 in isavga_suspend (dev=0xffffff0001632a00)
>    at /usr/src/sys/isa/vga_isa.c:234

The problem is on stack level 8. Line 538 in sys/dev/fb/vesa.c returns
NULL because x86bios_alloc(&offs, size); couldn't allocate memory. In
line 551 the nullpointer is passed to bcopy(), causing the crash. A
simple sollution is to add a nullpointer check like the attached patch
does. But I'm not sure if that's the right solution, since the VGA state
will not be saved if the check triggers.

--- vesa.c_	2010-07-01 20:38:54.000000000 +0200
+++ vesa.c	2010-07-01 20:38:03.000000000 +0200
@@ -536,6 +536,8 @@
 		return (1);

 	buf = x86bios_alloc(&offs, size);
+	if (buf == NULL)
+		return (1);

 	x86bios_init_regs(&regs);
 	regs.R_AX = 0x4f04;


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