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From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: linux-kernel@vger.kernel.org
Cc: tglx@linutronix.de, Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@redhat.com>,
	linux-mm@kvack.org, Shaohua Li <shli@kernel.org>,
	linux-raid@vger.kernel.org,
	Anna-Maria Gleixner <anna-maria@linutronix.de>,
	Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Subject: [PATCH 1/5] spinlock: atomic_dec_and_lock: Add an irqsave variant
Date: Fri,  4 May 2018 17:45:29 +0200	[thread overview]
Message-ID: <20180504154533.8833-2-bigeasy@linutronix.de> (raw)
In-Reply-To: <20180504154533.8833-1-bigeasy@linutronix.de>

From: Anna-Maria Gleixner <anna-maria@linutronix.de>

There are in-tree users of atomic_dec_and_lock() which must acquire the
spin lock with interrupts disabled. To workaround the lack of an irqsave
variant of atomic_dec_and_lock() they use local_irq_save() at the call
site. This causes extra code and creates in some places unneeded long
interrupt disabled times. These places need also extra treatment for
PREEMPT_RT due to the disconnect of the irq disabling and the lock
function.

Implement the missing irqsave variant of the function.

Signed-off-by: Anna-Maria Gleixner <anna-maria@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 include/linux/spinlock.h |  5 +++++
 lib/dec_and_lock.c       | 16 ++++++++++++++++
 2 files changed, 21 insertions(+)

diff --git a/include/linux/spinlock.h b/include/linux/spinlock.h
index 4894d322d258..803536c992f5 100644
--- a/include/linux/spinlock.h
+++ b/include/linux/spinlock.h
@@ -409,6 +409,11 @@ extern int _atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock);
 #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 *flags);
+#define atomic_dec_and_lock_irqsave(atomic, lock, flags) \
+		__cond_lock(lock, _atomic_dec_and_lock_irqsave(atomic, lock, &(flags)))
+
 int alloc_bucket_spinlocks(spinlock_t **locks, unsigned int *lock_mask,
 			   size_t max_size, unsigned int cpu_mult,
 			   gfp_t gfp);
diff --git a/lib/dec_and_lock.c b/lib/dec_and_lock.c
index 347fa7ac2e8a..9555b68bb774 100644
--- a/lib/dec_and_lock.c
+++ b/lib/dec_and_lock.c
@@ -33,3 +33,19 @@ int _atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock)
 }
 
 EXPORT_SYMBOL(_atomic_dec_and_lock);
+
+int _atomic_dec_and_lock_irqsave(atomic_t *atomic, spinlock_t *lock,
+				 unsigned long *flags)
+{
+	/* Subtract 1 from counter unless that drops it to 0 (ie. it was 1) */
+	if (atomic_add_unless(atomic, -1, 1))
+		return 0;
+
+	/* Otherwise do it the slow way */
+	spin_lock_irqsave(lock, *flags);
+	if (atomic_dec_and_test(atomic))
+		return 1;
+	spin_unlock_irqrestore(lock, *flags);
+	return 0;
+}
+EXPORT_SYMBOL(_atomic_dec_and_lock_irqsave);
-- 
2.17.0

  reply	other threads:[~2018-05-04 15:45 UTC|newest]

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-05-04 15:45 Introduce atomic_dec_and_lock_irqsave() Sebastian Andrzej Siewior
2018-05-04 15:45 ` Sebastian Andrzej Siewior [this message]
2018-06-04 10:25   ` [PATCH 1/5 v2] spinlock: atomic_dec_and_lock: Add an irqsave variant Sebastian Andrzej Siewior
2018-06-04 10:27     ` [PATCH 1.5/5] alpha: atomic: provide asm for the fastpath for _atomic_dec_and_lock_irqsave Sebastian Andrzej Siewior
2018-06-04 11:48       ` Peter Zijlstra
2018-06-04 12:55         ` Sebastian Andrzej Siewior
2018-06-06 11:18         ` [PATCH 0.5/5] alpha: remove custom dec_and_lock() implementation Sebastian Andrzej Siewior
2018-06-06 11:21           ` Sebastian Andrzej Siewior
2018-06-06 11:59           ` Peter Zijlstra
2018-06-12 21:36             ` [tip:locking/urgent] alpha: Remove " tip-bot for Sebastian Andrzej Siewior
2018-05-04 15:45 ` [PATCH 2/5] mm/backing-dev: Use irqsave variant of atomic_dec_and_lock() Sebastian Andrzej Siewior
2018-05-04 15:45 ` [PATCH 3/5] kernel/user: " Sebastian Andrzej Siewior
2018-05-04 15:45 ` [PATCH 4/5] drivers/md/raid5: " Sebastian Andrzej Siewior
2018-05-04 15:45 ` [PATCH 5/5] drivers/md/raid5: Do not disable irq on release_inactive_stripe_list() call Sebastian Andrzej Siewior
2018-05-04 15:54 ` Introduce atomic_dec_and_lock_irqsave() Peter Zijlstra
2018-05-04 16:07   ` Sebastian Andrzej Siewior
2018-05-04 16:21     ` Peter Zijlstra
2018-05-04 16:26       ` Al Viro
2018-05-04 16:38         ` Peter Zijlstra
2018-05-23 13:02 ` Peter Zijlstra
2018-05-30  9:26   ` Sebastian Andrzej Siewior

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