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[PATCH] sparc32 rwlock fix

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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: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Al Viro 2006-10-08 14:32:15 +01:00 • committed by Linus Torvalds
parent 6d24c8dc2e
commit 7a39f52202
3 changed files with 50 additions and 2 deletions
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4
arch/sparc/kernel/sparc_ksyms.c
View file

@ -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

20
arch/sparc/lib/locks.S
View file

@ -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