From: Hirokazu Takata <takata@linux-m32r.org>
Date: Tue, 21 Feb 2006 02:28:17 +0000 (-0800)
Subject: [PATCH] m32r: update sys_tas() routine
X-Git-Tag: v2.6.16-rc5~75
X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=cf535ea52e68e3ee6f4a90cc383faa1ee857f14d;p=linux-2.6

[PATCH] m32r: update sys_tas() routine

This patch updates and fixes sys_tas() routine for m32r.

In the previous implementation, a lockup rarely caused at sys_tas()
routine in SMP environment.

> > The problem is that touching *addr will generate an oops if that page isn't
> > paged in.  If we convert it to use get_user() then that's an improvement,
> > but we must not run get_user() under spinlock or local_irq_disable().

I rewrote sys_tas() routine by using "lock -> unlock" instructions, and
utilizing the m32r's interrupt handling characteristics; the m32r processor
can accept interrupts only at the 32-bit instruction boundary.  So, the
"unlock" instruction can be executed continuously after the "lock"
instruction execution without any interruptions.

In addition, to solve such a page_fault problem, I use a fixup code like
get_user().

And, as for the kernel lockup problem, we found that a calling
do_page_fault() routine with disabling interrupts might cause a lockup at
flush_tlb_others(), because we checked a completion of IPI handler's
operations in a spin-locked critical section.

Therefore, by using "lock -> unlock" code, we can implement the sys_tas()
rouitine without disabling interrupts explicitly, then no lockups would
happen at flush_tlb_others(), I hope.

Compile check and some working test in SMP environment have done.

Signed-off-by: Hirokazu Takata <takata@linux-m32r.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
---

diff --git a/arch/m32r/kernel/sys_m32r.c b/arch/m32r/kernel/sys_m32r.c
index fe55b28d37..670cb49210 100644
--- a/arch/m32r/kernel/sys_m32r.c
+++ b/arch/m32r/kernel/sys_m32r.c
@@ -29,28 +29,7 @@
 
 /*
  * sys_tas() - test-and-set
- * linuxthreads testing version
  */
-#ifndef CONFIG_SMP
-asmlinkage int sys_tas(int *addr)
-{
-	int oldval;
-	unsigned long flags;
-
-	if (!access_ok(VERIFY_WRITE, addr, sizeof (int)))
-		return -EFAULT;
-	local_irq_save(flags);
-	oldval = *addr;
-	if (!oldval)
-		*addr = 1;
-	local_irq_restore(flags);
-	return oldval;
-}
-#else /* CONFIG_SMP */
-#include <linux/spinlock.h>
-
-static DEFINE_SPINLOCK(tas_lock);
-
 asmlinkage int sys_tas(int *addr)
 {
 	int oldval;
@@ -58,15 +37,43 @@ asmlinkage int sys_tas(int *addr)
 	if (!access_ok(VERIFY_WRITE, addr, sizeof (int)))
 		return -EFAULT;
 
-	_raw_spin_lock(&tas_lock);
-	oldval = *addr;
-	if (!oldval)
-		*addr = 1;
-	_raw_spin_unlock(&tas_lock);
+	/* atomic operation:
+	 *   oldval = *addr; *addr = 1;
+	 */
+	__asm__ __volatile__ (
+		DCACHE_CLEAR("%0", "r4", "%1")
+		"	.fillinsn\n"
+		"1:\n"
+		"	lock	%0, @%1	    ->	unlock	%2, @%1\n"
+		"2:\n"
+		/* NOTE:
+		 *   The m32r processor can accept interrupts only
+		 *   at the 32-bit instruction boundary.
+		 *   So, in the above code, the "unlock" instruction
+		 *   can be executed continuously after the "lock"
+		 *   instruction execution without any interruptions.
+		 */
+		".section .fixup,\"ax\"\n"
+		"	.balign 4\n"
+		"3:	ldi	%0, #%3\n"
+		"	seth	r14, #high(2b)\n"
+		"	or3	r14, r14, #low(2b)\n"
+		"	jmp	r14\n"
+		".previous\n"
+		".section __ex_table,\"a\"\n"
+		"	.balign 4\n"
+		"	.long 1b,3b\n"
+		".previous\n"
+		: "=&r" (oldval)
+		: "r" (addr), "r" (1), "i"(-EFAULT)
+		: "r14", "memory"
+#ifdef CONFIG_CHIP_M32700_TS1
+		  , "r4"
+#endif /* CONFIG_CHIP_M32700_TS1 */
+	);
 
 	return oldval;
 }
-#endif /* CONFIG_SMP */
 
 /*
  * sys_pipe() is the normal C calling standard for creating