linux-kernel - Re: [PATCH v3 05/14] s390/pkey: Remove redundant rcu_read_lock/unlock() in spin

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Message-ID: <31be6bb6541bb3e338e3025ac9e8fce5@linux.ibm.com>
Date: Tue, 16 Sep 2025 12:51:03 +0200
From: Harald Freudenberger <freude@...ux.ibm.com>
To: pengdonglin <dolinux.peng@...il.com>
Cc: tj@...nel.org, tony.luck@...el.com, jani.nikula@...ux.intel.com,
        ap420073@...il.com, jv@...sburgh.net, bcrl@...ck.org,
        trondmy@...nel.org, longman@...hat.com, kees@...nel.org,
        bigeasy@...utronix.de, hdanton@...a.com, paulmck@...nel.org,
        linux-kernel@...r.kernel.org, linux-rt-devel@...ts.linux.dev,
        linux-nfs@...r.kernel.org, linux-aio@...ck.org,
        linux-fsdevel@...r.kernel.org, linux-security-module@...r.kernel.org,
        netdev@...r.kernel.org, intel-gfx@...ts.freedesktop.org,
        linux-wireless@...r.kernel.org, linux-acpi@...r.kernel.org,
        linux-s390@...r.kernel.org, cgroups@...r.kernel.org,
        Holger Dengler <dengler@...ux.ibm.com>,
        Vasily
 Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        pengdonglin <pengdonglin@...omi.com>
Subject: Re: [PATCH v3 05/14] s390/pkey: Remove redundant
 rcu_read_lock/unlock() in spin_lock

On 2025-09-16 06:47, pengdonglin wrote:
> From: pengdonglin <pengdonglin@...omi.com>
> 
> Since commit a8bb74acd8efe ("rcu: Consolidate RCU-sched update-side
> function definitions")
> there is no difference between rcu_read_lock(), rcu_read_lock_bh() and
> rcu_read_lock_sched() in terms of RCU read section and the relevant 
> grace
> period. That means that spin_lock(), which implies 
> rcu_read_lock_sched(),
> also implies rcu_read_lock().
> 
> There is no need no explicitly start a RCU read section if one has 
> already
> been started implicitly by spin_lock().
> 
> Simplify the code and remove the inner rcu_read_lock() invocation.
> 
> Cc: Harald Freudenberger <freude@...ux.ibm.com>
> Cc: Holger Dengler <dengler@...ux.ibm.com>
> Cc: Vasily Gorbik <gor@...ux.ibm.com>
> Cc: Alexander Gordeev <agordeev@...ux.ibm.com>
> Signed-off-by: pengdonglin <pengdonglin@...omi.com>
> Signed-off-by: pengdonglin <dolinux.peng@...il.com>
> ---
>  drivers/s390/crypto/pkey_base.c | 3 ---
>  1 file changed, 3 deletions(-)
> 
> diff --git a/drivers/s390/crypto/pkey_base.c 
> b/drivers/s390/crypto/pkey_base.c
> index b15741461a63..4c4a9feecccc 100644
> --- a/drivers/s390/crypto/pkey_base.c
> +++ b/drivers/s390/crypto/pkey_base.c
> @@ -48,16 +48,13 @@ int pkey_handler_register(struct pkey_handler 
> *handler)
> 
>  	spin_lock(&handler_list_write_lock);
> 
> -	rcu_read_lock();
>  	list_for_each_entry_rcu(h, &handler_list, list) {
>  		if (h == handler) {
> -			rcu_read_unlock();
>  			spin_unlock(&handler_list_write_lock);
>  			module_put(handler->module);
>  			return -EEXIST;
>  		}
>  	}
> -	rcu_read_unlock();
> 
>  	list_add_rcu(&handler->list, &handler_list);
>  	spin_unlock(&handler_list_write_lock);

Acked-by: Harald Freudenberger <freude@...ux.ibm.com>