Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit cf535ea5 authored by Hirokazu Takata's avatar Hirokazu Takata Committed by Linus Torvalds
Browse files

[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: default avatarHirokazu Takata <takata@linux-m32r.org>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent b04ec261

arch/m32r/kernel/sys_m32r.c

+34 −27
Original line number Diff line number Diff line
@@ -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