OpenVZ Forum


Home » Mailing lists » Devel » BC: resource beancounters (v6) (with userpages reclamation + configfs)
[PATCH 1/13] BC: atomic_dec_and_lock_irqsave() helper [message #8161 is a reply to message #8159] Thu, 09 November 2006 16:47 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.bcprep 2006-11-03 17:46:25.000000000 +0300
+++ ./include/linux/spinlock.h 2006-11-03 17:46:31.000000000 +0300
@@ -319,6 +319,12 @@ 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.bcprep 2006-11-03 17:46:25.000000000 +0300
+++ ./kernel/user.c 2006-11-03 17:46:31.000000000 +0300
@@ -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.bcprep 2006-11-03 17:46:25.000000000 +0300
+++ ./lib/dec_and_lock.c 2006-11-03 17:46:31.000000000 +0300
@@ -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
Read Message
Read Message
Read Message
Read Message
Read Message
Previous Topic: Re: Re: [RFC] [PATCH 0/4] uid_ns: introduction
Next Topic: [PATCH] ext3: small fix for previous retries patch in ext3_prepare_write()
Goto Forum:
  

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

Current Time: Mon Sep 08 02:02:14 GMT 2025

Total time taken to generate the page: 0.08009 seconds
Powered by FUDforum Powered by Virtuozzo Containers