From ccfbb5bed407053b27492a9adc06064d949a9aa6 Mon Sep 17 00:00:00 2001
From: Anna-Maria Gleixner <anna-maria@linutronix.de>
Date: Tue, 12 Jun 2018 18:16:20 +0200
Subject: [PATCH] atomic: Add irqsave variant of atomic_dec_and_lock()
Git-commit: ccfbb5bed407053b27492a9adc06064d949a9aa6
Patch-mainline: v4.18-rc2
References: bsc#1111974 bsc#1166003
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>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r20180612161621.22645-3-bigeasy@linutronix.de
Acked-by: Coly Li <colyli@suse.de>
---
include/linux/spinlock.h | 5 +++++
lib/dec_and_lock.c | 16 ++++++++++++++++
2 files changed, 21 insertions(+)
--- a/include/linux/spinlock.h
+++ b/include/linux/spinlock.h
@@ -408,4 +408,9 @@ 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 *flags);
+#define atomic_dec_and_lock_irqsave(atomic, lock, flags) \
+ __cond_lock(lock, _atomic_dec_and_lock_irqsave(atomic, lock, &(flags)))
+
#endif /* __LINUX_SPINLOCK_H */
--- a/lib/dec_and_lock.c
+++ b/lib/dec_and_lock.c
@@ -32,3 +32,19 @@ int _atomic_dec_and_lock(atomic_t *atomi
}
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);