[PATCH] m32r: update sys_tas() routine (cf535ea5) · Commits · 戴 / test

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>

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

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