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[PATCH] m32r: update sys_tas() routine

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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>
This commit is contained in:
Hirokazu Takata 2006-02-20 18:28:17 -08:00 committed by Linus Torvalds
parent b04ec261bd
commit cf535ea52e
1 changed files with 34 additions and 27 deletions
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61
arch/m32r/kernel/sys_m32r.c
View file

@ -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