[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@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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 @@
: /* 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 @@
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()