linux-kernel - Re: [PATCH 3/6] powerpc: fadump: use lock guard for mutex

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Message-ID: <20250314082223.GT5880@noisy.programming.kicks-ass.net>
Date: Fri, 14 Mar 2025 09:22:23 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Shrikanth Hegde <sshegde@...ux.ibm.com>
Cc: maddy@...ux.ibm.com, linuxppc-dev@...ts.ozlabs.org, npiggin@...il.com,
	christophe.leroy@...roup.eu, mpe@...erman.id.au,
	fbarrat@...ux.ibm.com, ajd@...ux.ibm.com, mahesh@...ux.ibm.com,
	oohall@...il.com, hbathini@...ux.ibm.com, dhowells@...hat.com,
	haren@...ux.ibm.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/6] powerpc: fadump: use lock guard for mutex

On Fri, Mar 14, 2025 at 11:15:41AM +0530, Shrikanth Hegde wrote:
> use guard(mutex) for scope based resource management of mutex.
> This would make the code simpler and easier to maintain.
> 
> More details on lock guards can be found at
> https://lore.kernel.org/all/20230612093537.614161713@infradead.org/T/#u
> 
> Signed-off-by: Shrikanth Hegde <sshegde@...ux.ibm.com>
> ---
>  arch/powerpc/kernel/fadump.c | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/fadump.c b/arch/powerpc/kernel/fadump.c
> index 4b371c738213..5fd2c546fd8c 100644
> --- a/arch/powerpc/kernel/fadump.c
> +++ b/arch/powerpc/kernel/fadump.c
> @@ -1374,15 +1374,13 @@ static void fadump_free_elfcorehdr_buf(void)
>  
>  static void fadump_invalidate_release_mem(void)
>  {
> -	mutex_lock(&fadump_mutex);
> +	guard(mutex)(&fadump_mutex);
> +
>  	if (!fw_dump.dump_active) {
> -		mutex_unlock(&fadump_mutex);
>  		return;
>  	}
>  
>  	fadump_cleanup();
> -	mutex_unlock(&fadump_mutex);
> -

This will result in running the below functions with the mutex held.

>  	fadump_free_elfcorehdr_buf();
>  	fadump_release_memory(fw_dump.boot_mem_top, memblock_end_of_DRAM());
>  	fadump_free_cpu_notes_buf();


The equivalent transformation for the above code would look like:

static void fadump_invalidate_release_mem(void)
{
	scoped_guard (mutex, &fadump_mutex) {
		if (!fw_dump.dump_active)
			return;

		fadump_cleanup();
	}

	fadump_free_elfcorehdr_buf();
	...