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

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Message-ID: <333198fd-e028-42cb-8847-bd5ddd2a623b@linux.ibm.com>
Date: Fri, 14 Mar 2025 14:57:13 +0530
From: Shrikanth Hegde <sshegde@...ux.ibm.com>
To: Peter Zijlstra <peterz@...radead.org>
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 3/14/25 13:55, Peter Zijlstra wrote:
> 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.
> 

Yes. Got it. let me use scoped_guard for it as well. There is get_user 
and other things in the fail parse and having it with mutex will not be 
good.

I went through the rest of the patches too. It is mostly return after 
mutex.

Only in Patch 5/6 there is additional debug statement. Let me put a 
comment there.

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