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Message-ID: <20061008133215.GL29920@ftp.linux.org.uk>
Date: Sun, 8 Oct 2006 14:32:15 +0100
From: Al Viro <viro@....linux.org.uk>
To: davem@...emloft.net
Cc: Linus Torvalds <torvalds@...l.org>, linux-kernel@...r.kernel.org
Subject: [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: Al Viro <viro@...iv.linux.org.uk>
---
arch/sparc/kernel/sparc_ksyms.c | 4 +++-
arch/sparc/lib/locks.S | 20 ++++++++++++++++++++
include/asm-sparc/spinlock.h | 28 +++++++++++++++++++++++++++-
3 files changed, 50 insertions(+), 2 deletions(-)
diff --git a/arch/sparc/kernel/sparc_ksyms.c b/arch/sparc/kernel/sparc_ksyms.c
index 4d441a5..33dadd9 100644
--- a/arch/sparc/kernel/sparc_ksyms.c
+++ b/arch/sparc/kernel/sparc_ksyms.c
@@ -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
diff --git a/arch/sparc/lib/locks.S b/arch/sparc/lib/locks.S
index 95fa484..b1df55c 100644
--- a/arch/sparc/lib/locks.S
+++ b/arch/sparc/lib/locks.S
@@ -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
diff --git a/include/asm-sparc/spinlock.h b/include/asm-sparc/spinlock.h
index 557d089..de2249b 100644
--- a/include/asm-sparc/spinlock.h
+++ b/include/asm-sparc/spinlock.h
@@ -129,6 +129,7 @@ static inline void __raw_write_lock(raw_
: /* 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(ra
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()
--
1.4.2.GIT
-
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