Hi Linus, Christoph,
I'm not sure what happened, but I think I applied an old incomplete patch when
patching 2.5.28, one that was missing Christoph's rwsem-spinlock stuff and the
trylock stuff. The attached patch adds these back (as per Christoph's patch),
it also adds a missing export to lib/rwsem.c.
When compiled for PentiumIII SMP, I see:
dhowells>nm vmlinux | grep rwsem
c01c5dbd t .text.lock.rwsem
c02995a0 ? __kstrtab_rwsem_down_read_failed
c02995b7 ? __kstrtab_rwsem_down_write_failed
c02995da ? __kstrtab_rwsem_downgrade_wake
c02995cf ? __kstrtab_rwsem_wake
c02a1cf8 ? __ksymtab_rwsem_down_read_failed
c02a1d00 ? __ksymtab_rwsem_down_write_failed
c02a1d10 ? __ksymtab_rwsem_downgrade_wake
c02a1d08 ? __ksymtab_rwsem_wake
c01c5870 T rwsem_down_read_failed
c01c5a20 T rwsem_down_write_failed
c01c5cf0 T rwsem_downgrade_wake
c01c5bd0 T rwsem_wake
When compiled for i386 SMP, I see:
dhowells>nm vmlinux | grep 'rwsem\|__\(up\|down.*\)_\(read\|write\)'
c01be49a t .text.lock.rwsem_spinlock
c01bdf8c T __down_read
c01be080 T __down_read_trylock
c01be0f4 T __down_write
c01be1ec T __down_write_trylock
c01be3e4 T __downgrade_write
c028c0f9 ? __kstrtab___down_read
c028c120 ? __kstrtab___down_read_trylock
c028c142 ? __kstrtab___down_write
c028c160 ? __kstrtab___down_write_trylock
c028c1c0 ? __kstrtab___downgrade_write
c028c183 ? __kstrtab___up_read
c028c19b ? __kstrtab___up_write
c028c0e0 ? __kstrtab_init_rwsem
c0295b80 ? __ksymtab___down_read
c0295b88 ? __ksymtab___down_read_trylock
c0295b90 ? __ksymtab___down_write
c0295b98 ? __ksymtab___down_write_trylock
c0295bb0 ? __ksymtab___downgrade_write
c0295ba0 ? __ksymtab___up_read
c0295ba8 ? __ksymtab___up_write
c0295b78 ? __ksymtab_init_rwsem
c01be264 T __up_read
c01be2fc T __up_write
c01bdf6c T init_rwsem
So I think I've got all the functions there and that they're all exported now.
David
diff -uNr linux-2.5.29/include/asm-i386/rwsem.h linux-rwsem-2529/include/asm-i386/rwsem.h
--- linux-2.5.29/include/asm-i386/rwsem.h Mon Jul 29 08:26:56 2002
+++ linux-rwsem-2529/include/asm-i386/rwsem.h Mon Jul 29 08:32:49 2002
@@ -118,6 +118,29 @@
}
/*
+ * trylock for reading -- returns 1 if successful, 0 if contention
+ */
+static inline int __down_read_trylock(struct rw_semaphore *sem)
+{
+ __s32 result, tmp;
+ __asm__ __volatile__(
+ "# beginning __down_read_trylock\n\t"
+ " movl %0,%1\n\t"
+ "1:\n\t"
+ " movl %1,%2\n\t"
+ " addl %3,%2\n\t"
+ " jle 2f\n\t"
+LOCK_PREFIX " cmpxchgl %2,%0\n\t"
+ " jnz 1b\n\t"
+ "2:\n\t"
+ "# ending __down_read_trylock\n\t"
+ : "+m"(sem->count), "=&a"(result), "=&r"(tmp)
+ : "i"(RWSEM_ACTIVE_READ_BIAS)
+ : "memory", "cc");
+ return result>=0 ? 1 : 0;
+}
+
+/*
* lock for writing
*/
static inline void __down_write(struct rw_semaphore *sem)
@@ -145,6 +168,19 @@
}
/*
+ * trylock for writing -- returns 1 if successful, 0 if contention
+ */
+static inline int __down_write_trylock(struct rw_semaphore *sem)
+{
+ signed long ret = cmpxchg(&sem->count,
+ RWSEM_UNLOCKED_VALUE,
+ RWSEM_ACTIVE_WRITE_BIAS);
+ if (ret == RWSEM_UNLOCKED_VALUE)
+ return 1;
+ return 0;
+}
+
+/*
* unlock after reading
*/
static inline void __up_read(struct rw_semaphore *sem)
diff -uNr linux-2.5.29/include/linux/rwsem-spinlock.h linux-rwsem-2529/include/linux/rwsem-spinlock.h
--- linux-2.5.29/include/linux/rwsem-spinlock.h Thu Jul 11 19:35:21 2002
+++ linux-rwsem-2529/include/linux/rwsem-spinlock.h Mon Jul 29 08:32:49 2002
@@ -54,9 +54,12 @@
extern void FASTCALL(init_rwsem(struct rw_semaphore *sem));
extern void FASTCALL(__down_read(struct rw_semaphore *sem));
+extern int FASTCALL(__down_read_trylock(struct rw_semaphore *sem));
extern void FASTCALL(__down_write(struct rw_semaphore *sem));
+extern int FASTCALL(__down_write_trylock(struct rw_semaphore *sem));
extern void FASTCALL(__up_read(struct rw_semaphore *sem));
extern void FASTCALL(__up_write(struct rw_semaphore *sem));
+extern void FASTCALL(__downgrade_write(struct rw_semaphore *sem));
#endif /* __KERNEL__ */
#endif /* _LINUX_RWSEM_SPINLOCK_H */
diff -uNr linux-2.5.29/include/linux/rwsem.h linux-rwsem-2529/include/linux/rwsem.h
--- linux-2.5.29/include/linux/rwsem.h Mon Jul 29 08:26:57 2002
+++ linux-rwsem-2529/include/linux/rwsem.h Mon Jul 29 08:32:49 2002
@@ -46,6 +46,18 @@
}
/*
+ * trylock for reading -- returns 1 if successful, 0 if contention
+ */
+static inline int down_read_trylock(struct rw_semaphore *sem)
+{
+ int ret;
+ rwsemtrace(sem,"Entering down_read_trylock");
+ ret = __down_read_trylock(sem);
+ rwsemtrace(sem,"Leaving down_read_trylock");
+ return ret;
+}
+
+/*
* lock for writing
*/
static inline void down_write(struct rw_semaphore *sem)
@@ -56,6 +68,18 @@
}
/*
+ * trylock for writing -- returns 1 if successful, 0 if contention
+ */
+static inline int down_write_trylock(struct rw_semaphore *sem)
+{
+ int ret;
+ rwsemtrace(sem,"Entering down_write_trylock");
+ ret = __down_write_trylock(sem);
+ rwsemtrace(sem,"Leaving down_write_trylock");
+ return ret;
+}
+
+/*
* release a read lock
*/
static inline void up_read(struct rw_semaphore *sem)
@@ -85,6 +109,5 @@
rwsemtrace(sem,"Leaving downgrade_write");
}
-
#endif /* __KERNEL__ */
#endif /* _LINUX_RWSEM_H */
diff -uNr linux-2.5.29/lib/rwsem-spinlock.c linux-rwsem-2529/lib/rwsem-spinlock.c
--- linux-2.5.29/lib/rwsem-spinlock.c Thu Jul 11 19:35:17 2002
+++ linux-rwsem-2529/lib/rwsem-spinlock.c Mon Jul 29 08:32:49 2002
@@ -46,8 +46,9 @@
* - the 'waiting count' is non-zero
* - the spinlock must be held by the caller
* - woken process blocks are discarded from the list after having flags zeroised
+ * - writers are only woken if wakewrite is non-zero
*/
-static inline struct rw_semaphore *__rwsem_do_wake(struct rw_semaphore *sem)
+static inline struct rw_semaphore *__rwsem_do_wake(struct rw_semaphore *sem, int wakewrite)
{
struct rwsem_waiter *waiter;
int woken;
@@ -56,7 +57,14 @@
waiter = list_entry(sem->wait_list.next,struct rwsem_waiter,list);
- /* try to grant a single write lock if there's a writer at the front of the queue
+ if (!wakewrite) {
+ if (waiter->flags & RWSEM_WAITING_FOR_WRITE)
+ goto out;
+ goto dont_wake_writers;
+ }
+
+ /* if we are allowed to wake writers try to grant a single write lock if there's a
+ * writer at the front of the queue
* - we leave the 'waiting count' incremented to signify potential contention
*/
if (waiter->flags & RWSEM_WAITING_FOR_WRITE) {
@@ -68,16 +76,19 @@
}
/* grant an infinite number of read locks to the readers at the front of the queue */
+ dont_wake_writers:
woken = 0;
- do {
+ while (waiter->flags&RWSEM_WAITING_FOR_READ) {
+ struct list_head *next = waiter->list.next;
+
list_del(&waiter->list);
waiter->flags = 0;
wake_up_process(waiter->task);
woken++;
if (list_empty(&sem->wait_list))
break;
- waiter = list_entry(sem->wait_list.next,struct rwsem_waiter,list);
- } while (waiter->flags&RWSEM_WAITING_FOR_READ);
+ waiter = list_entry(next,struct rwsem_waiter,list);
+ }
sem->activity += woken;
@@ -149,6 +160,28 @@
}
/*
+ * trylock for reading -- returns 1 if successful, 0 if contention
+ */
+int __down_read_trylock(struct rw_semaphore *sem)
+{
+ int ret = 0;
+ rwsemtrace(sem,"Entering __down_read_trylock");
+
+ spin_lock(&sem->wait_lock);
+
+ if (sem->activity>=0 && list_empty(&sem->wait_list)) {
+ /* granted */
+ sem->activity++;
+ ret = 1;
+ }
+
+ spin_unlock(&sem->wait_lock);
+
+ rwsemtrace(sem,"Leaving __down_read_trylock");
+ return ret;
+}
+
+/*
* get a write lock on the semaphore
* - note that we increment the waiting count anyway to indicate an exclusive lock
*/
@@ -195,6 +228,28 @@
}
/*
+ * trylock for writing -- returns 1 if successful, 0 if contention
+ */
+int __down_write_trylock(struct rw_semaphore *sem)
+{
+ int ret = 0;
+ rwsemtrace(sem,"Entering __down_write_trylock");
+
+ spin_lock(&sem->wait_lock);
+
+ if (sem->activity==0 && list_empty(&sem->wait_list)) {
+ /* granted */
+ sem->activity = -1;
+ ret = 1;
+ }
+
+ spin_unlock(&sem->wait_lock);
+
+ rwsemtrace(sem,"Leaving __down_write_trylock");
+ return ret;
+}
+
+/*
* release a read lock on the semaphore
*/
void __up_read(struct rw_semaphore *sem)
@@ -222,18 +277,40 @@
sem->activity = 0;
if (!list_empty(&sem->wait_list))
- sem = __rwsem_do_wake(sem);
+ sem = __rwsem_do_wake(sem, 1);
spin_unlock(&sem->wait_lock);
rwsemtrace(sem,"Leaving __up_write");
}
+/*
+ * downgrade a write lock into a read lock
+ * - just wake up any readers at the front of the queue
+ */
+void __downgrade_write(struct rw_semaphore *sem)
+{
+ rwsemtrace(sem,"Entering __rwsem_downgrade");
+
+ spin_lock(&sem->wait_lock);
+
+ sem->activity = 1;
+ if (!list_empty(&sem->wait_list))
+ sem = __rwsem_do_wake(sem,0);
+
+ spin_unlock(&sem->wait_lock);
+
+ rwsemtrace(sem,"Leaving __rwsem_downgrade");
+}
+
EXPORT_SYMBOL(init_rwsem);
EXPORT_SYMBOL(__down_read);
+EXPORT_SYMBOL(__down_read_trylock);
EXPORT_SYMBOL(__down_write);
+EXPORT_SYMBOL(__down_write_trylock);
EXPORT_SYMBOL(__up_read);
EXPORT_SYMBOL(__up_write);
+EXPORT_SYMBOL(__downgrade_write);
#if RWSEM_DEBUG
EXPORT_SYMBOL(rwsemtrace);
#endif
diff -uNr linux-2.5.29/lib/rwsem.c linux-rwsem-2529/lib/rwsem.c
--- linux-2.5.29/lib/rwsem.c Mon Jul 29 08:26:57 2002
+++ linux-rwsem-2529/lib/rwsem.c Mon Jul 29 08:35:47 2002
@@ -236,6 +236,7 @@
EXPORT_SYMBOL_NOVERS(rwsem_down_read_failed);
EXPORT_SYMBOL_NOVERS(rwsem_down_write_failed);
EXPORT_SYMBOL_NOVERS(rwsem_wake);
+EXPORT_SYMBOL_NOVERS(rwsem_downgrade_wake);
#if RWSEM_DEBUG
EXPORT_SYMBOL(rwsemtrace);
#endif
-
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This archive was generated by hypermail 2b29 : Tue Jul 30 2002 - 14:00:32 EST