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

[Ira Weiny]

On Thu, Jun 04, 2020 at 12:41:33PM +0300, Mike Rapoport wrote:
> 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...

FWIW I got s390 to compile and this patch fixes s390 booting for me as well.

13:05:25 > /home/iweiny/dev/linux-build-test/rootfs/s390/run-qemu-s390.sh 
Build reference: next-20200603-4-g840714292d8c

Building s390:defconfig:initrd ... running ........... passed
Building s390:defconfig:virtio-blk-ccw:rootfs ... running ........... passed
Building s390:defconfig:scsi[virtio-ccw]:rootfs ... running ..............  passed
Building s390:defconfig:virtio-pci:rootfs ... running ........... passed
Building s390:defconfig:scsi[virtio-pci]:rootfs ... running ........... passed

Ira

> 
> @Peter, @Thomas, can you comment please?
> 
> From e51d50ee6f4d1f446decf91c2c67230da14ff82c Mon Sep 17 00:00:00 2001
> From: Mike Rapoport <rppt@xxxxxxxxxxxxx>
> 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@xxxxxxxxxxxxx>
> ---
>  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.