[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 fe55b28..670cb49 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 @@
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