OpenVZ Forum


Home » Mailing lists » Devel » [PATCH] BC: resource beancounters (v3)
[PATCH 1/7] introduce atomic_dec_and_lock_irqsave() [message #5740 is a reply to message #5738] Tue, 29 August 2006 14:47 Go to previous messageGo to previous message
dev is currently offline  dev
Messages: 1693
Registered: September 2005
Location: Moscow
Senior Member
Oleg Nesterov noticed to me that the construction like
(used in beancounter patches and free_uid()):

local_irq_save(flags);
if (atomic_dec_and_lock(&refcnt, &lock))
...

is not that good for preemtible kernels, since with preemption
spin_lock() can schedule() to reduce latency. However, it won't schedule
if interrupts are disabled.

So this patch introduces atomic_dec_and_lock_irqsave() as a logical
counterpart to atomic_dec_and_lock().

Signed-Off-By: Pavel Emelianov <xemul@sw.ru>
Signed-Off-By: Kirill Korotaev <dev@sw.ru>

---

include/linux/spinlock.h | 6 ++++++
kernel/user.c | 5 +----
lib/dec_and_lock.c | 19 +++++++++++++++++++
3 files changed, 26 insertions(+), 4 deletions(-)

--- ./include/linux/spinlock.h.dlirq 2006-08-28 10:17:35.000000000 +0400
+++ ./include/linux/spinlock.h 2006-08-28 11:22:37.000000000 +0400
@@ -266,6 +266,12 @@ extern int _atomic_dec_and_lock(atomic_t
#define atomic_dec_and_lock(atomic, lock) \
__cond_lock(lock, _atomic_dec_and_lock(atomic, lock))

+extern int _atomic_dec_and_lock_irqsave(atomic_t *atomic, spinlock_t *lock,
+ unsigned long *flagsp);
+#define atomic_dec_and_lock_irqsave(atomic, lock, flags) \
+ __cond_lock(lock, \
+ _atomic_dec_and_lock_irqsave(atomic, lock, &flags))
+
/**
* spin_can_lock - would spin_trylock() succeed?
* @lock: the spinlock in question.
--- ./kernel/user.c.dlirq 2006-07-10 12:39:20.000000000 +0400
+++ ./kernel/user.c 2006-08-28 11:08:56.000000000 +0400
@@ -108,15 +108,12 @@ void free_uid(struct user_struct *up)
if (!up)
return;

- local_irq_save(flags);
- if (atomic_dec_and_lock(&up->__count, &uidhash_lock)) {
+ if (atomic_dec_and_lock_irqsave(&up->__count, &uidhash_lock, flags)) {
uid_hash_remove(up);
spin_unlock_irqrestore(&uidhash_lock, flags);
key_put(up->uid_keyring);
key_put(up->session_keyring);
kmem_cache_free(uid_cachep, up);
- } else {
- local_irq_restore(flags);
}
}

--- ./lib/dec_and_lock.c.dlirq 2006-04-21 11:59:36.000000000 +0400
+++ ./lib/dec_and_lock.c 2006-08-28 11:22:08.000000000 +0400
@@ -33,3 +33,22 @@ int _atomic_dec_and_lock(atomic_t *atomi
}

EXPORT_SYMBOL(_atomic_dec_and_lock);
+
+/*
+ * the same, but takes the lock with _irqsave
+ */
+int _atomic_dec_and_lock_irqsave(atomic_t *atomic, spinlock_t *lock,
+ unsigned long *flagsp)
+{
+#ifdef CONFIG_SMP
+ if (atomic_add_unless(atomic, -1, 1))
+ return 0;
+#endif
+ spin_lock_irqsave(lock, *flagsp);
+ if (atomic_dec_and_test(atomic))
+ return 1;
+ spin_unlock_irqrestore(lock, *flagsp);
+ return 0;
+}
+
+EXPORT_SYMBOL(_atomic_dec_and_lock_irqsave);

Report message to a moderator

[Message index]
 
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Previous Topic: [PATCH] neigh_table_clear() doesn't free stats
Next Topic: [PATCH] ext3: wrong error behavior
Goto Forum:
  

[ Syndicate this forum (XML) ] [ RSS ] [ PDF ]

Current Time: Sat Jul 27 16:13:12 GMT 2024

Total time taken to generate the page: 0.02675 seconds
Powered by FUDforum Powered by Virtuozzo Containers