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

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Message-ID: <87bjznyliv.fsf@gmail.com>
Date: Mon, 14 Oct 2024 16:54:56 +0530
From: Ritesh Harjani (IBM) <ritesh.list@...il.com>
To: Madhavan Srinivasan <maddy@...ux.ibm.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

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.

>
>
>> 
>> 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