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

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Message-ID: <1263bf89-a2dd-4ae9-a8f9-9c36ddd08208@linux.ibm.com>
Date: Fri, 14 Mar 2025 14:38:04 +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 3/6] powerpc: fadump: use lock guard for mutex



On 3/14/25 13:52, Peter Zijlstra wrote:

Thanks Peter for taking a look.

> 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();
> 

Ok. Got it, since the variable is still in scope unlock wont be called.
So, will use scoped_guard as you suggested below in v2.

> 
> 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();
> 	...

ok.