Re: [PATCH] arch/{mips,sparc,microblaze,powerpc}: Don't enable pagefault/preempt twice

[Mike Rapoport <rppt@kernel.org>]

On Wed, Jun 03, 2020 at 04:44:17PM -0700, Guenter Roeck wrote:
> 
> sparc32 smp images in next-20200603 still crash for me with a spinlock
> recursion. s390 images hang early in boot. Several others (alpha, arm64,
> various ppc) don't even compile. I can run some more bisects over time,
> but this is becoming a full-time job :-(.

I've been able to bisect s390 hang to commit b614345f52bc ("x86/entry:
Clarify irq_{enter,exit}_rcu()").

After this commit, lockdep_hardirq_exit() is called twice on s390 (and
others) - one time in irq_exit_rcu() and another one in irq_exit():

/**
 * irq_exit_rcu() - Exit an interrupt context without updating RCU
 *
 * Also processes softirqs if needed and possible.
 */
void irq_exit_rcu(void)
{
	__irq_exit_rcu();
	 /* must be last! */
	lockdep_hardirq_exit();
}

/**
 * irq_exit - Exit an interrupt context, update RCU and lockdep
 *
 * Also processes softirqs if needed and possible.
 */
void irq_exit(void)
{
	irq_exit_rcu();
	rcu_irq_exit();
	 /* must be last! */
	lockdep_hardirq_exit();
}

Removing the call in irq_exit() make s390 boot again, and judgung by the
x86 entry code, the comment /* must be last! */ is stale...

@Peter, @Thomas, can you comment please?

From e51d50ee6f4d1f446decf91c2c67230da14ff82c Mon Sep 17 00:00:00 2001
From: Mike Rapoport <rppt@linux.ibm.com>
Date: Thu, 4 Jun 2020 12:37:03 +0300
Subject: [PATCH] softirq: don't call lockdep_hardirq_exit() twice

After commit b614345f52bc ("x86/entry: Clarify irq_{enter,exit}_rcu()")
lockdep_hardirq_exit() is called twice on every architecture that uses
irq_exit(): one time in irq_exit_rcu() and another one in irq_exit().

Remove the extra call in irq_exit().

Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
---
 kernel/softirq.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/kernel/softirq.c b/kernel/softirq.c
index a3eb6eba8c41..7523f4ce4c1d 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -427,7 +427,6 @@ static inline void __irq_exit_rcu(void)
 void irq_exit_rcu(void)
 {
 	__irq_exit_rcu();
-	 /* must be last! */
 	lockdep_hardirq_exit();
 }
 
@@ -440,8 +439,6 @@ void irq_exit(void)
 {
 	irq_exit_rcu();
 	rcu_irq_exit();
-	 /* must be last! */
-	lockdep_hardirq_exit();
 }
 
 /*
-- 
2.26.2



> Guenter

-- 
Sincerely yours,
Mike.