linux-kernel - Re: [RFC v3 1/3] fadump: Refactor and prepare fadump_cma

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Message-ID: <b66e69a9-7098-44f6-822d-f19bfe85117d@linux.ibm.com>
Date: Fri, 18 Oct 2024 20:24:28 +0530
From: Madhavan Srinivasan <maddy@...ux.ibm.com>
To: "Ritesh Harjani (IBM)" <ritesh.list@...il.com>,
        linuxppc-dev@...ts.ozlabs.org
Cc: linux-mm@...ck.org, Sourabh Jain <sourabhjain@...ux.ibm.com>,
        Hari Bathini <hbathini@...ux.ibm.com>, Zi Yan <ziy@...dia.com>,
        David Hildenbrand <david@...hat.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Mahesh J Salgaonkar <mahesh@...ux.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        "Aneesh Kumar K . V" <aneesh.kumar@...nel.org>,
        Donet Tom <donettom@...ux.vnet.ibm.com>,
        LKML
 <linux-kernel@...r.kernel.org>,
        Sachin P Bappalige <sachinpb@...ux.ibm.com>
Subject: Re: [RFC v3 1/3] fadump: Refactor and prepare fadump_cma_init for
 late init



On 10/14/24 4:54 PM, Ritesh Harjani (IBM) wrote:
> Madhavan Srinivasan <maddy@...ux.ibm.com> writes:
> 
>> On 10/11/24 8:30 PM, Ritesh Harjani (IBM) wrote:
>>> We anyway don't use any return values from fadump_cma_init(). Since
>>> fadump_reserve_mem() from where fadump_cma_init() gets called today,
>>> already has the required checks.
>>> This patch makes this function return type as void. Let's also handle
>>> extra cases like return if fadump_supported is false or dump_active, so
>>> that in later patches we can call fadump_cma_init() separately from
>>> setup_arch().
>>
>> Usually patches to this file are posted with title format of
>>
>> powerpc/fadump:<>
> 
> yes. I guess it is good to do it that way (I might have missed it)
> Although commit history of oldest few patches to fadump shows..
> 
> ebaeb5ae2437 fadump: Convert firmware-assisted cpu state dump data into elf notes.
> 2df173d9e85d fadump: Initialize elfcore header and add PT_LOAD program headers.
> 3ccc00a7e04f fadump: Register for firmware assisted dump.
> eb39c8803d0e fadump: Reserve the memory for firmware assisted dump.
> 
>>

Patchset looks fine to me. 

Reviewed-by: Madhavan Srinivasan <maddy@...ux.ibm.com> for the series.


>>
>>>
>>> Acked-by: Hari Bathini <hbathini@...ux.ibm.com>
>>> Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@...il.com>
>>> ---
>>> v2 -> v3: Separated the series into 2 as discussed in v2.
>>> [v2]: https://lore.kernel.org/linuxppc-dev/cover.1728585512.git.ritesh.list@gmail.com/
>>>
>>>  arch/powerpc/kernel/fadump.c | 23 +++++++++--------------
>>>  1 file changed, 9 insertions(+), 14 deletions(-)
>>>
>>> diff --git a/arch/powerpc/kernel/fadump.c b/arch/powerpc/kernel/fadump.c
>>> index a612e7513a4f..162327d66982 100644
>>> --- a/arch/powerpc/kernel/fadump.c
>>> +++ b/arch/powerpc/kernel/fadump.c
>>> @@ -78,27 +78,23 @@ static struct cma *fadump_cma;
>>>   * But for some reason even if it fails we still have the memory reservation
>>>   * with us and we can still continue doing fadump.
>>>   */
>>> -static int __init fadump_cma_init(void)
>>> +static void __init fadump_cma_init(void)
>>>  {
>>>  	unsigned long long base, size;
>>>  	int rc;
>>>
>>> -	if (!fw_dump.fadump_enabled)
>>> -		return 0;
>>> -
>>> +	if (!fw_dump.fadump_supported || !fw_dump.fadump_enabled ||
>>> +			fw_dump.dump_active)
>>> +		return;
>>
>> Is these checks even needed here? fadump_reserve_mem() checked for all
>> these already, also dont see any other caller for fadump_cma_init(). 
>>
>>
> 
> In the next patch we will move fadump_cma_init() call from within
> fadump_reserve_mem() to setup_arch(). Hence we need these extra checks
> in fadump_cma_init() as well. I mentioned the same in the commit msg of
> this patch too.
> 
>>>  	/*
>>>  	 * Do not use CMA if user has provided fadump=nocma kernel parameter.
>>> -	 * Return 1 to continue with fadump old behaviour.
>>>  	 */
>>> -	if (fw_dump.nocma)
>>> -		return 1;
>>> +	if (fw_dump.nocma || !fw_dump.boot_memory_size)
>>> +		return;
>>>
>>>  	base = fw_dump.reserve_dump_area_start;
>>>  	size = fw_dump.boot_memory_size;
>>>
>>> -	if (!size)
>>> -		return 0;
>>
>> So this is the only place where we return 0, which in turn will make the
>> "ret" in fadump_reserve_mem() as zero forcing to call reserve_crashkernel()
>> in early_init_devtree().
>>
>> we are removing it, becos we know "size" here will never be zero?
>>
>>
> 
> yes. Because we already check if boot_memory_size is less than
> bootmem_min in fadump_reserve_mem(). If it is less, then we fail and
> disable fadump (fadump_enabled = 0).
> 
> So then there is no need to check for !boot_memory_size in here.
> 
> fadump_reseve_mem( ) {
> <...>
> 	if (!fw_dump.dump_active) {
> 		fw_dump.boot_memory_size =
> 			PAGE_ALIGN(fadump_calculate_reserve_size());
> 
> 		bootmem_min = fw_dump.ops->fadump_get_bootmem_min();
> 		if (fw_dump.boot_memory_size < bootmem_min) {
> 			pr_err("Can't enable fadump with boot memory size (0x%lx) less than 0x%llx\n",
> 			       fw_dump.boot_memory_size, bootmem_min);
> 			goto error_out;
> 		}
>     <...>    
>     }
> <...>
> error_out:
> 	fw_dump.fadump_enabled = 0;
> 	fw_dump.reserve_dump_area_size = 0;
> 	return 0;
> }
> 
> 
> Thanks for the review!
> -ritesh