Hi,
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.
-- Takata
From: Hirokazu Takata <[email protected]>
Subject: Re: [WTF?] sys_tas() on m32r
Date: Tue, 27 Dec 2005 14:27:39 +0900 (JST)
> Hi,
>
> From: Andrew Morton <[email protected]>
> Date: Fri, 23 Dec 2005 05:55:26 -0800
> > Al Viro <[email protected]> wrote:
> > >
> > > 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;
> > > }
> > > in arch/m32r/kernel/sys_m32r.c. Trivial oops *AND* ability to trigger
> > > IO with interrupts disabled.
> >
> > Yeah. I pointed this out to Takata in October last year and then promptly
> > forgot about it. It's rather amazing that this code (which appears to be in
> > live use in linuxthreads) hasn't generated oopses.
>
> Yes, I remember it.
>
> > 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().
>
> Exactly.
> This problem has been bothering me, but I cannot find a good solusion...
Signed-off-by: Hirokazu Takata <[email protected]>
---
arch/m32r/kernel/sys_m32r.c | 61 ++++++++++++++++++++++++--------------------
1 file changed, 34 insertions(+), 27 deletions(-)
Index: linux-2.6.16-rc1/arch/m32r/kernel/sys_m32r.c
===================================================================
--- linux-2.6.16-rc1.orig/arch/m32r/kernel/sys_m32r.c 2006-01-31 21:47:06.918951364 +0900
+++ linux-2.6.16-rc1/arch/m32r/kernel/sys_m32r.c 2006-01-31 21:58:21.733388614 +0900
@@ -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
--
Hirokazu Takata <[email protected]>
Linux/M32R Project: http://www.linux-m32r.org/
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
[Index of Archives]
[Kernel Newbies]
[Netfilter]
[Bugtraq]
[Photo]
[Stuff]
[Gimp]
[Yosemite News]
[MIPS Linux]
[ARM Linux]
[Linux Security]
[Linux RAID]
[Video 4 Linux]
[Linux for the blind]
[Linux Resources]
