Messages in this thread Patch in this message | | | Date | Thu, 09 Nov 2006 19:53:14 +0300 | From | Kirill Korotaev <> | Subject | [PATCH 1/13] BC: atomic_dec_and_lock_irqsave() helper |
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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); - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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