Commit 7a39f522 authored by Al Viro's avatar Al Viro Committed by Linus Torvalds
Browse files

[PATCH] sparc32 rwlock fix 



read_trylock() is broken on sparc32 (doesn't build and didn't work
right, actually).  Proposed fix:

 - make "writer holds lock" distinguishable from "reader tries to grab
   lock"

 - have __raw_read_trylock() try to acquire the mutex (in LSB of lock),
   terminating spin if we see that there's writer holding it.  Then do
   the rest as we do in read_lock().

Thanks to Ingo for discussion...

Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 6d24c8dc

arch/sparc/kernel/sparc_ksyms.c

+3 −1
Original line number Diff line number Diff line
@@ -87,6 +87,7 @@ extern void ___set_bit(void); 
extern void ___clear_bit(void);

extern void ___change_bit(void);

extern void ___rw_read_enter(void);

extern void ___rw_read_try(void);

extern void ___rw_read_exit(void);

extern void ___rw_write_enter(void);
@@ -104,8 +105,9 @@ extern unsigned _Urem(unsigned, unsigned); 
EXPORT_SYMBOL(sparc_cpu_model);

EXPORT_SYMBOL(kernel_thread);

#ifdef CONFIG_SMP

// XXX find what uses (or used) these.

// XXX find what uses (or used) these.   AV: see asm/spinlock.h

EXPORT_SYMBOL(___rw_read_enter);

EXPORT_SYMBOL(___rw_read_try);

EXPORT_SYMBOL(___rw_read_exit);

EXPORT_SYMBOL(___rw_write_enter);

#endif

arch/sparc/lib/locks.S

+20 −0
Original line number Diff line number Diff line
@@ -25,6 +25,15 @@ ___rw_read_enter_spin_on_wlock: 
	 ldstub	[%g1 + 3], %g2

	b	___rw_read_enter_spin_on_wlock

	 ldub	[%g1 + 3], %g2

___rw_read_try_spin_on_wlock:

	andcc	%g2, 0xff, %g0

	be,a	___rw_read_try

	 ldstub	[%g1 + 3], %g2

	xnorcc	%g2, 0x0, %o0	/* if g2 is ~0, set o0 to 0 and bugger off */

	bne,a	___rw_read_enter_spin_on_wlock

	 ld	[%g1], %g2

	retl

	 mov	%g4, %o7

___rw_read_exit_spin_on_wlock:

	orcc	%g2, 0x0, %g0

	be,a	___rw_read_exit
@@ -60,6 +69,17 @@ ___rw_read_exit: 
	retl

	 mov	%g4, %o7



	.globl	___rw_read_try

___rw_read_try:

	orcc	%g2, 0x0, %g0

	bne	___rw_read_try_spin_on_wlock

	 ld	[%g1], %g2

	add	%g2, 1, %g2

	st	%g2, [%g1]

	set	1, %o1

	retl

	 mov	%g4, %o7



	.globl	___rw_write_enter

___rw_write_enter:

	orcc	%g2, 0x0, %g0

include/asm-sparc/spinlock.h

+27 −1
Original line number Diff line number Diff line
@@ -129,6 +129,7 @@ static inline void __raw_write_lock(raw_rwlock_t *rw) 
	: /* no outputs */

	: "r" (lp)

	: "g2", "g4", "memory", "cc");

	*(volatile __u32 *)&lp->lock = ~0U;

}



static inline int __raw_write_trylock(raw_rwlock_t *rw)
@@ -144,15 +145,40 @@ static inline int __raw_write_trylock(raw_rwlock_t *rw) 
		val = rw->lock & ~0xff;

		if (val)

			((volatile u8*)&rw->lock)[3] = 0;

		else

			*(volatile u32*)&rw->lock = ~0U;

	}



	return (val == 0);

}



static inline int __read_trylock(raw_rwlock_t *rw)

{

	register raw_rwlock_t *lp asm("g1");

	register int res asm("o0");

	lp = rw;

	__asm__ __volatile__(

	"mov	%%o7, %%g4\n\t"

	"call	___rw_read_try\n\t"

	" ldstub	[%%g1 + 3], %%g2\n"

	: "=r" (res)

	: "r" (lp)

	: "g2", "g4", "memory", "cc");

	return res;

}



#define __raw_read_trylock(lock) \

({	unsigned long flags; \

	int res; \

	local_irq_save(flags); \

	res = __read_trylock(lock); \

	local_irq_restore(flags); \

	res; \

})



#define __raw_write_unlock(rw)	do { (rw)->lock = 0; } while(0)



#define __raw_spin_lock_flags(lock, flags) __raw_spin_lock(lock)

#define __raw_read_trylock(lock) generic__raw_read_trylock(lock)



#define _raw_spin_relax(lock)	cpu_relax()

#define _raw_read_relax(lock)	cpu_relax()

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