linux-kernel - Re: [PATCH 4/6] powerpc: book3s: vas: use lock guard for mutex

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Message-ID: <20250314082527.GU5880@noisy.programming.kicks-ass.net>
Date: Fri, 14 Mar 2025 09:25:27 +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 4/6] powerpc: book3s: vas: use lock guard for mutex

On Fri, Mar 14, 2025 at 11:15:42AM +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
> 
> There is also an example of using scoped_guard. 
> 
> Signed-off-by: Shrikanth Hegde <sshegde@...ux.ibm.com>
> ---
>  arch/powerpc/platforms/book3s/vas-api.c | 19 ++++++-------------
>  1 file changed, 6 insertions(+), 13 deletions(-)
> 
> diff --git a/arch/powerpc/platforms/book3s/vas-api.c b/arch/powerpc/platforms/book3s/vas-api.c
> index 0b6365d85d11..eb1a97271afb 100644
> --- a/arch/powerpc/platforms/book3s/vas-api.c
> +++ b/arch/powerpc/platforms/book3s/vas-api.c
> @@ -425,7 +425,7 @@ static vm_fault_t vas_mmap_fault(struct vm_fault *vmf)
>  		return VM_FAULT_SIGBUS;
>  	}
>  
> -	mutex_lock(&txwin->task_ref.mmap_mutex);
> +	guard(mutex)(&txwin->task_ref.mmap_mutex);
>  	/*
>  	 * The window may be inactive due to lost credit (Ex: core
>  	 * removal with DLPAR). If the window is active again when
> @@ -437,11 +437,9 @@ static vm_fault_t vas_mmap_fault(struct vm_fault *vmf)
>  		if (paste_addr) {
>  			fault = vmf_insert_pfn(vma, vma->vm_start,
>  					(paste_addr >> PAGE_SHIFT));
> -			mutex_unlock(&txwin->task_ref.mmap_mutex);
>  			return fault;
>  		}
>  	}
> -	mutex_unlock(&txwin->task_ref.mmap_mutex);

I had to open up this file to check, but this seems incorrect since you
now also run do_fail_paste() with the lock held, where previously you
did not.


>  	/*
>  	 * Received this fault due to closing the actual window.