Date: Tue, 25 Sep 2001 04:35:25 -0700 From: Julian Elischer <julian@elischer.org> To: Peter Wemm <peter@wemm.org> Cc: Matt Dillon <dillon@earth.backplane.com>, Ian Dowse <iedowse@maths.tcd.ie>, hackers@FreeBSD.ORG Subject: Re: Patch to test kstack usage. Message-ID: <3BB06BFD.F1870676@elischer.org> References: <20010925051923.6CA2F3808@overcee.netplex.com.au>
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Peter Wemm wrote:
>
> Matt Dillon wrote:
> > This isn't perfect but it should be a good start in regards to
> > testing kstack use. This patch is against -stable. It reports
> > kernel stack use on process exit and will generate a 'Kernel stack
> > underflow' message if it detects an underflow. It doesn't panic,
> > so for a fun time you can leave UPAGES at 2 and watch in horror.
>
> It is checking against the wrong guard value. It should be u_guard2.
>
> FWIW; the max stack available is 4688 bytes on a standard 4.x system. Yes,
> that is too freaking close. Also, the maximum usage depends on what sort
> of cards you have in the system.. If you have a heavy tty user (eg: a 32+
> port serial card) then you have lots of tty interrupts nesting as well.
> Having the ppp/sl/plip drivers in the system partly negates the effect of
> this though since it wires the net/tty interrupt masks together.
usb devices allocate 2K on the stack so if you have them too.......
so does openning an atapi cdrom...
so a combination of interrupts and those, might consume 4K
>
> peter@thunder[10:13pm]~-111> ./tu
> stack base = 3504
> stack size = 4688
> peter@thunder[10:13pm]~-112> cat tu.c
> #include <sys/param.h>
> #include <sys/user.h>
> #include <stdio.h>
> #include <stddef.h>
>
> int
> main(int ac, char **av)
> {
> int stack_base = offsetof(struct user, u_kproc);
>
> printf("stack base = %d\n", stack_base);
> printf("stack size = %d\n", UPAGES * PAGE_SIZE - stack_base);
> }
>
> > --- sys/user.h 1999/12/29 04:24:49 1.24
> > +++ sys/user.h 2001/09/25 03:41:04
> > @@ -109,9 +109,13 @@
> > * Remaining fields only for core dump and/or ptrace--
> > * not valid at other times!
> > */
> > + u_int32_t u_guard2; /* guard the base of the kstack */
> > struct kinfo_proc u_kproc; /* proc + eproc */
> > struct md_coredump u_md; /* machine dependent glop */
> > + u_int32_t u_guard; /* guard the base of the kstack */
> > };
>
> Cheers,
> -Peter
> --
> Peter Wemm - peter@FreeBSD.org; peter@yahoo-inc.com; peter@netplex.com.au
> "All of this is for nothing if we don't go to the stars" - JMS/B5
--
+------------------------------------+ ______ _ __
| __--_|\ Julian Elischer | \ U \/ / hard at work in
| / \ julian@elischer.org +------>x USA \ a very strange
| ( OZ ) \___ ___ | country !
+- X_.---._/ presently in San Francisco \_/ \\
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