Date: Thu, 2 Oct 2014 21:54:56 -0400 From: Larry Baird <lab@gta.com> To: Konstantin Belousov <kostikbel@gmail.com> Cc: "freebsd-hackers@freebsd.org" <freebsd-hackers@freebsd.org>, Ryan Stone <rysto32@gmail.com>, Dimitry Andric <dim@FreeBSD.org>, Bryan Drewery <bdrewery@FreeBSD.org> Subject: Re: Kernel/Compiler bug Message-ID: <20141003015456.GA27080@gta.com> In-Reply-To: <20141002143345.GY26076@kib.kiev.ua> References: <20141001031553.GA14360@gta.com> <CAFMmRNxAYcr8eEY0SJsX3zkRadjT29-mfsGcSTmG_Yx-Hidi6w@mail.gmail.com> <20141001134044.GA57022@gta.com> <FBB9E4C3-55B9-4917-9953-F8BC9AE43619@FreeBSD.org> <542C8C75.30007@FreeBSD.org> <20141002075537.GU26076@kib.kiev.ua> <20141002140232.GA52387@gta.com> <20141002143345.GY26076@kib.kiev.ua>
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> The easiest thing to do is to record the stack depth for kernel mode
> on entry into interrupt. Interrupt handlers are usually well written
> and do not consume a lot of stack.
>
> Look at the intr_event_handle(), which is the entry point. The mode can
> be deduced from trapframe passed. The kernel stack for the thread is
> described by td->td_kstack (base, i.e. bottom) and td->td_kstack_pages
> (size), so the top of the stack is at td_kstack + td_kstack_size [*].
> The current stack consumption could be taken from reading %rsp register,
> or you may take the address of any local variable as well.
>
> * - there are pcb and usermode fpu save area at the top of the stack, and
> actual kernel stack top is right below fpu save area. This should not
> be important for your measurements, since you are looking at how close
> the %rsp gets to the bottom.
This idea worked very well. Booting a GENERIC 10.1-BETA3 kernel I get a
maximum stack used of 5247 bytes. This was with a minimal virtual box
configuration. It would be interesting to hear about users with more exotic
hardware and or configurations. Not sure if I have the KASSERT correct.
Index: kern_intr.c
===================================================================
--- kern_intr.c (revision 44897)
+++ kern_intr.c (working copy)
@@ -1386,6 +1386,12 @@
}
}
+static int max_kern_thread_stack;
+
+SYSCTL_INT(_kern, OID_AUTO, max_kern_thread_stack, CTLFLAG_RD,
+ &max_kern_thread_stack, 0,
+ "Maxiumum stack used by a kernel thread");
+
/*
* Main interrupt handling body.
*
@@ -1407,6 +1413,22 @@
td = curthread;
+ /*
+ * Check for maximum stack used bya kernel thread.
+ */
+ if (!TRAPF_USERMODE(frame)) {
+ char *top = (char *)(td->td_kstack + td->td_kstack_pages *
+ PAGE_SIZE - 1);
+ char *current = (char *)&ih;
+ int used = top - current;
+
+ if (used > max_kern_thread_stack) {
+ max_kern_thread_stack = used;
+ KASSERT(max_kern_thread_stack < KSTACK_PAGES * PAGE_SIZE,
+ "Maximum kernel thread stack exxceeded");
+ }
+ }
+
/* An interrupt with no event or handlers is a stray interrupt. */
if (ie == NULL || TAILQ_EMPTY(&ie->ie_handlers))
return (EINVAL);
--
------------------------------------------------------------------------
Larry Baird
Global Technology Associates, Inc. 1992-2012 | http://www.gta.com
Celebrating Twenty Years of Software Innovation | Orlando, FL
Email: lab@gta.com | TEL 407-380-0220
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