linux-kernel - Re: [PATCH v1 07/11] fs/proc/vmcore: introduce PROC_VMCORE_DEVICE_RAM to detect device RAM ranges in 2nd kernel

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Message-ID: <3866cec8-9983-4adf-b96e-42fa728c84a8@redhat.com>
Date: Fri, 22 Nov 2024 10:47:45 +0100
From: David Hildenbrand <david@...hat.com>
To: Baoquan He <bhe@...hat.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
 linux-s390@...r.kernel.org, virtualization@...ts.linux.dev,
 kvm@...r.kernel.org, linux-fsdevel@...r.kernel.org,
 kexec@...ts.infradead.org, Heiko Carstens <hca@...ux.ibm.com>,
 Vasily Gorbik <gor@...ux.ibm.com>, Alexander Gordeev
 <agordeev@...ux.ibm.com>, Christian Borntraeger <borntraeger@...ux.ibm.com>,
 Sven Schnelle <svens@...ux.ibm.com>, "Michael S. Tsirkin" <mst@...hat.com>,
 Jason Wang <jasowang@...hat.com>, Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
 Eugenio Pérez <eperezma@...hat.com>,
 Vivek Goyal <vgoyal@...hat.com>, Dave Young <dyoung@...hat.com>,
 Thomas Huth <thuth@...hat.com>, Cornelia Huck <cohuck@...hat.com>,
 Janosch Frank <frankja@...ux.ibm.com>,
 Claudio Imbrenda <imbrenda@...ux.ibm.com>, Eric Farman
 <farman@...ux.ibm.com>, Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v1 07/11] fs/proc/vmcore: introduce PROC_VMCORE_DEVICE_RAM
 to detect device RAM ranges in 2nd kernel

On 22.11.24 08:31, Baoquan He wrote:
> On 10/25/24 at 05:11pm, David Hildenbrand wrote:
> ......snip...
>> diff --git a/fs/proc/vmcore.c b/fs/proc/vmcore.c
>> index 3e90416ee54e..c332a9a4920b 100644
>> --- a/fs/proc/vmcore.c
>> +++ b/fs/proc/vmcore.c
>> @@ -69,6 +69,8 @@ static LIST_HEAD(vmcore_cb_list);
>>   /* Whether the vmcore has been opened once. */
>>   static bool vmcore_opened;
>>   
>> +static void vmcore_process_device_ram(struct vmcore_cb *cb);
>> +
>>   void register_vmcore_cb(struct vmcore_cb *cb)
>>   {
>>   	INIT_LIST_HEAD(&cb->next);
>> @@ -80,6 +82,8 @@ void register_vmcore_cb(struct vmcore_cb *cb)
>>   	 */
>>   	if (vmcore_opened)
>>   		pr_warn_once("Unexpected vmcore callback registration\n");
>> +	else if (cb->get_device_ram)
>> +		vmcore_process_device_ram(cb);
> 
> Global variable 'vmcore_opened' is used to indicate if /proc/vmcore is
> opened. With &vmcore_mutex, we don't need to worry about concurrent
> opening and modification. However, if people just open /proc/vmcore and
> close it after checking, then s390 will miss the vmcore dumping, is it
> acceptable?

See my reply to your other mail (patch #3).

> 
>>   	mutex_unlock(&vmcore_mutex);
>>   }
>>   EXPORT_SYMBOL_GPL(register_vmcore_cb);
>> @@ -1511,6 +1515,158 @@ int vmcore_add_device_dump(struct vmcoredd_data *data)
> ......
>> +
>> +static void vmcore_process_device_ram(struct vmcore_cb *cb)
>> +{
>> +	unsigned char *e_ident = (unsigned char *)elfcorebuf;
>> +	struct vmcore_mem_node *first, *m;
>> +	LIST_HEAD(list);
>> +	int count;
>> +
>> +	if (cb->get_device_ram(cb, &list)) {
>> +		pr_err("Kdump: obtaining device ram ranges failed\n");
>> +		return;
>> +	}
>> +	count = list_count_nodes(&list);
>> +	if (!count)
>> +		return;
>> +
>> +	/* We only support Elf64 dumps for now. */
>> +	if (WARN_ON_ONCE(e_ident[EI_CLASS] != ELFCLASS64)) {
>> +		pr_err("Kdump: device ram ranges only support Elf64\n");
>> +		goto out_free;
>> +	}
> 
> Only supporting Elf64 dumps seems to be a basic checking, do we need
> to put it at the beginning of function? Otherwise, we spend efforts to
> call cb->get_device_ram(), then fail.

The idea was that if there is nothing to add, then the elf class doesn't 
matter. But yes, I can move this further up.

Thanks!

-- 
Cheers,

David / dhildenb