[PATCH] powerpc/pseries: Fix dtl_access_lock to be a rw_semaphore

[Nysal Jan K.A.]

On Mon, Aug 19, 2024 at 10:24:01PM GMT, Michael Ellerman wrote:

<snip>

> Fixes: 06220d78f24a ("powerpc/pseries: Introduce rwlock to gatekeep DTLB usage")
> Signed-off-by: Michael Ellerman <mpe at ellerman.id.au>
> ---
>  arch/powerpc/include/asm/dtl.h        | 3 ++-
>  arch/powerpc/platforms/pseries/dtl.c  | 8 ++++----
>  arch/powerpc/platforms/pseries/lpar.c | 8 ++++----
>  3 files changed, 10 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/dtl.h b/arch/powerpc/include/asm/dtl.h
> index d6f43d149f8d..e21bac6c065c 100644
> --- a/arch/powerpc/include/asm/dtl.h
> +++ b/arch/powerpc/include/asm/dtl.h
> @@ -1,6 +1,7 @@
>  #ifndef _ASM_POWERPC_DTL_H
>  #define _ASM_POWERPC_DTL_H
>  
> +#include <linux/rwsem.h>
>  #include <asm/lppaca.h>
>  #include <linux/spinlock_types.h>

The above include is redundant now and can be removed.

Reviewed-by: Nysal Jan K.A <nysal at linux.ibm.com>

>  
> @@ -35,7 +36,7 @@ struct dtl_entry {
>  #define DTL_LOG_ALL		(DTL_LOG_CEDE | DTL_LOG_PREEMPT | DTL_LOG_FAULT)
>  
>  extern struct kmem_cache *dtl_cache;
> -extern rwlock_t dtl_access_lock;
> +extern struct rw_semaphore dtl_access_lock;
>  
>  extern void register_dtl_buffer(int cpu);
>  extern void alloc_dtl_buffers(unsigned long *time_limit);
> diff --git a/arch/powerpc/platforms/pseries/dtl.c b/arch/powerpc/platforms/pseries/dtl.c
> index 3f1cdccebc9c..ecc04ef8c53e 100644
> --- a/arch/powerpc/platforms/pseries/dtl.c
> +++ b/arch/powerpc/platforms/pseries/dtl.c
> @@ -191,7 +191,7 @@ static int dtl_enable(struct dtl *dtl)
>  		return -EBUSY;
>  
>  	/* ensure there are no other conflicting dtl users */
> -	if (!read_trylock(&dtl_access_lock))
> +	if (!down_read_trylock(&dtl_access_lock))
>  		return -EBUSY;
>  
>  	n_entries = dtl_buf_entries;
> @@ -199,7 +199,7 @@ static int dtl_enable(struct dtl *dtl)
>  	if (!buf) {
>  		printk(KERN_WARNING "%s: buffer alloc failed for cpu %d\n",
>  				__func__, dtl->cpu);
> -		read_unlock(&dtl_access_lock);
> +		up_read(&dtl_access_lock);
>  		return -ENOMEM;
>  	}
>  
> @@ -217,7 +217,7 @@ static int dtl_enable(struct dtl *dtl)
>  	spin_unlock(&dtl->lock);
>  
>  	if (rc) {
> -		read_unlock(&dtl_access_lock);
> +		up_read(&dtl_access_lock);
>  		kmem_cache_free(dtl_cache, buf);
>  	}
>  
> @@ -232,7 +232,7 @@ static void dtl_disable(struct dtl *dtl)
>  	dtl->buf = NULL;
>  	dtl->buf_entries = 0;
>  	spin_unlock(&dtl->lock);
> -	read_unlock(&dtl_access_lock);
> +	up_read(&dtl_access_lock);
>  }
>  
>  /* file interface */
> diff --git a/arch/powerpc/platforms/pseries/lpar.c b/arch/powerpc/platforms/pseries/lpar.c
> index c1d8bee8f701..bb09990eec30 100644
> --- a/arch/powerpc/platforms/pseries/lpar.c
> +++ b/arch/powerpc/platforms/pseries/lpar.c
> @@ -169,7 +169,7 @@ struct vcpu_dispatch_data {
>   */
>  #define NR_CPUS_H	NR_CPUS
>  
> -DEFINE_RWLOCK(dtl_access_lock);
> +DECLARE_RWSEM(dtl_access_lock);
>  static DEFINE_PER_CPU(struct vcpu_dispatch_data, vcpu_disp_data);
>  static DEFINE_PER_CPU(u64, dtl_entry_ridx);
>  static DEFINE_PER_CPU(struct dtl_worker, dtl_workers);
> @@ -463,7 +463,7 @@ static int dtl_worker_enable(unsigned long *time_limit)
>  {
>  	int rc = 0, state;
>  
> -	if (!write_trylock(&dtl_access_lock)) {
> +	if (!down_write_trylock(&dtl_access_lock)) {
>  		rc = -EBUSY;
>  		goto out;
>  	}
> @@ -479,7 +479,7 @@ static int dtl_worker_enable(unsigned long *time_limit)
>  		pr_err("vcpudispatch_stats: unable to setup workqueue for DTL processing\n");
>  		free_dtl_buffers(time_limit);
>  		reset_global_dtl_mask();
> -		write_unlock(&dtl_access_lock);
> +		up_write(&dtl_access_lock);
>  		rc = -EINVAL;
>  		goto out;
>  	}
> @@ -494,7 +494,7 @@ static void dtl_worker_disable(unsigned long *time_limit)
>  	cpuhp_remove_state(dtl_worker_state);
>  	free_dtl_buffers(time_limit);
>  	reset_global_dtl_mask();
> -	write_unlock(&dtl_access_lock);
> +	up_write(&dtl_access_lock);
>  }
>  
>  static ssize_t vcpudispatch_stats_write(struct file *file, const char __user *p,
> -- 
> 2.46.0
> 
>