linux-kernel - Re: [PATCH 1/4] Blackfin: arch patch for 2.6.18

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Message-Id: <200609251905.22224.arnd@arndb.de>
Date:	Mon, 25 Sep 2006 19:05:21 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Aubrey <aubreylee@...il.com>
Cc:	"Luke Yang" <luke.adi@...il.com>, linux-kernel@...r.kernel.org,
	"Andrew Morton" <akpm@...l.org>
Subject: Re: [PATCH 1/4] Blackfin: arch patch for 2.6.18

On Monday 25 September 2006 17:39, Aubrey wrote:
> 1) Timer interrupt will call do_irq(), then return_from_int().
> 
> 2) return_from_int() will check if there is interrupt pending or
> signal pending, if so, it will call schedule_and_signal_from_int().
> 
> 3) schedule_and_signal_from_int() will jump to resume_userspace()
> 
> 4) resume_userspace() will call _schedule to run the user task.

I have a little trouble reading your assembly code, but your
return_from_int() function should normally not call
schedule_and_signal_from_int() when the interrupt happened
in kernel context (like in the idle function):

+	/* if not return to user mode, get out */
+	p2.l = lo(IPEND);
+	p2.h = hi(IPEND);
+	r0 = [p2];
+	r1 = 0x17(Z);
+	r2 = ~r1;
+	r2.h = 0;
+	r0 = r2 & r0;
+	r1 = 1;
+	r1 = r0 - r1;
+	r2 = r0 & r1;
+	cc = r2 == 0;
+	if !cc jump 2f;

This looks a lot like you user_mode() function, so you jump
over schedule_and_signal_from_int() here.

What you described would be a preemptive kernel
(CONFIG_PREEMPT), but you clearly don't have that enabled.

	Arnd <><
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