[RFC PATCH 26/30] softirq: Increment the softirq offset on top of enabled bits

[Frederic Weisbecker <frederic@kernel.org>]

Now we can rely on the vector enabled bits to know if some vector is
disabled. Hence we can also now drive the softirq offset on top of it.

As a result, the softirq offset don't need to nest anymore as the vector
enable mask does it on the stack on its behalf:

	// Start with local_bh_disabled() == SOFTIRQ_ALL_MASK
	...
	bh = local_bh_disable(BIT(NET_RX_SOFTIRQ)) {
		bh = local_bh_disabled();
		local_bh_disabled() &= ~BIT(NET_RX_SOFTIRQ);
		// First vector disabled, inc preempt count
		preempt_count += SOFTIRQ_DISABLE_OFFSET;
		return bh;
	}
	....
		bh2 = local_bh_disable(BIT(BLOCK_SOFTIRQ)) {
			bh2 = local_bh_disabled();
			local_bh_disabled() &= ~BIT(NET_RX_SOFTIRQ);
			// No need to inc preempt count
			return bh2;
		}
		...
		local_bh_enable(bh2) {
			local_bh_disabled() = bh2;
			// No need to dec preempt count
		}
		...
	local_bh_enable(bh1) {
		local_bh_disabled() = bh;
		preempt_count -= SOFTIRQ_DISABLE_OFFSET;
	}

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: David S. Miller <davem@davemloft.net>
Cc: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/softirq.c | 25 ++++++++++++++++---------
 1 file changed, 16 insertions(+), 9 deletions(-)

diff --git a/kernel/softirq.c b/kernel/softirq.c
index e2435b0..84da16c 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -117,6 +117,10 @@ unsigned int __local_bh_disable_ip(unsigned long ip, unsigned int cnt,
 
 	raw_local_irq_save(flags);
 
+	enabled = local_softirq_enabled();
+	if (enabled != SOFTIRQ_ALL_MASK)
+		cnt &= ~SOFTIRQ_MASK;
+
 	/*
 	 * The preempt tracer hooks into preempt_count_add and will break
 	 * lockdep because it calls back into lockdep after SOFTIRQ_OFFSET
@@ -131,7 +135,6 @@ unsigned int __local_bh_disable_ip(unsigned long ip, unsigned int cnt,
 	if (softirq_count() == (cnt & SOFTIRQ_MASK))
 		trace_softirqs_off(ip);
 
-	enabled = local_softirq_enabled();
 	softirq_enabled_nand(mask);
 	raw_local_irq_restore(flags);
 
@@ -157,6 +160,9 @@ void local_bh_enable_no_softirq(unsigned int bh)
 
 	softirq_enabled_set(bh);
 
+	if (bh != SOFTIRQ_ALL_MASK)
+		return;
+			
 	if (preempt_count() == SOFTIRQ_DISABLE_OFFSET)
 		trace_preempt_on(CALLER_ADDR0, get_lock_parent_ip());
 
@@ -175,18 +181,18 @@ void __local_bh_enable_ip(unsigned long ip, unsigned int cnt, unsigned int bh)
 	local_irq_disable();
 #endif
 	softirq_enabled_set(bh);
-
-	/*
-	 * Are softirqs going to be turned on now:
-	 */
-	if (softirq_count() == SOFTIRQ_DISABLE_OFFSET)
+	if (bh != SOFTIRQ_ALL_MASK) {
+		cnt &= ~SOFTIRQ_MASK;
+	} else if (!(softirq_count() & SOFTIRQ_OFFSET)) {
+		/* Are softirqs going to be turned on now: */
 		trace_softirqs_on(ip);
+	}
 	/*
 	 * Keep preemption disabled until we are done with
 	 * softirq processing:
 	 */
-	preempt_count_sub(cnt - 1);
-
+	if (cnt)
+		preempt_count_sub(cnt - 1);
 
 	if (unlikely(!in_interrupt() && local_softirq_pending())) {
 		/*
@@ -196,7 +202,8 @@ void __local_bh_enable_ip(unsigned long ip, unsigned int cnt, unsigned int bh)
 		do_softirq();
 	}
 
-	preempt_count_dec();
+	if (cnt)
+		preempt_count_dec();
 #ifdef CONFIG_TRACE_IRQFLAGS
 	local_irq_enable();
 #endif
-- 
2.7.4