linux-kernel - Re: [PATCH v2 1/7] s390/kdump: implement is_kdump

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Message-ID: <a3f310d0-b878-44c4-9454-f7faf8be04ad@redhat.com>
Date: Tue, 15 Oct 2024 12:40:59 +0200
From: David Hildenbrand <david@...hat.com>
To: Heiko Carstens <hca@...ux.ibm.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
 linux-s390@...r.kernel.org, virtualization@...ts.linux.dev,
 linux-doc@...r.kernel.org, kvm@...r.kernel.org,
 Vasily Gorbik <gor@...ux.ibm.com>, Alexander Gordeev
 <agordeev@...ux.ibm.com>, Christian Borntraeger <borntraeger@...ux.ibm.com>,
 Sven Schnelle <svens@...ux.ibm.com>, Thomas Huth <thuth@...hat.com>,
 Cornelia Huck <cohuck@...hat.com>, Janosch Frank <frankja@...ux.ibm.com>,
 Claudio Imbrenda <imbrenda@...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>, Andrew Morton <akpm@...ux-foundation.org>,
 Jonathan Corbet <corbet@....net>, Mario Casquero <mcasquer@...hat.com>,
 Alexander Egorenkov <egorenar@...ux.ibm.com>,
 Mikhail Zaslonko <zaslonko@...ux.ibm.com>
Subject: Re: [PATCH v2 1/7] s390/kdump: implement is_kdump_kernel()

On 15.10.24 12:08, Heiko Carstens wrote:
> On Tue, Oct 15, 2024 at 10:41:21AM +0200, David Hildenbrand wrote:
>> On 15.10.24 10:30, Heiko Carstens wrote:
>>> On Mon, Oct 14, 2024 at 09:26:03PM +0200, David Hildenbrand wrote:
>>>> On 14.10.24 20:20, Heiko Carstens wrote:
>>>>> Looks like this could work. But the comment in smp.c above
>>>>> dump_available() needs to be updated.
>>>>
>>>> A right, I remember that there was some outdated documentation.
> 
> ...
> 
>> My concern is that we'll now have
>>
>> bool is_kdump_kernel(void)
>> {
>>         return oldmem_data.start && !is_ipl_type_dump();
>> }
>>
>> Which matches 3), but if 2) is also called "kdump", then should it actually
>> be
>>
>> bool is_kdump_kernel(void)
>> {
>>         return oldmem_data.start;
>> }
>>
>> ?
>>
>> When I wrote that code I was rather convinced that the variant in this patch
>> is the right thing to do.
> 
> Oh well, we simply of too many dump options. I'll let Alexander and
> Mikhail better comment on this :)

Thanks!

> 
> Alexander, Mikhail, the discussion starts here, and we need a sane
> is_kdump_kernel() for s390:
> https://lore.kernel.org/all/20241014144622.876731-1-david@redhat.com/
> 

With the following cleanup in mind:

 From 9fbbff43f725a8482ce9e85857316ab8484ff3c8 Mon Sep 17 00:00:00 2001
From: David Hildenbrand <david@...hat.com>
Date: Tue, 15 Oct 2024 11:07:43 +0200
Subject: [PATCH] s390: use !dump_available() instead of "!oldmem_data.start &&
  !is_ipl_type_dump()"

Let's make the code more readable:

    !dump_available()
-> !(oldmem_data.start || is_ipl_type_dump())
-> !oldmem_data.start && !is_ipl_type_dump()

Signed-off-by: David Hildenbrand <david@...hat.com>
---
  arch/s390/kernel/crash_dump.c | 2 +-
  arch/s390/kernel/os_info.c    | 2 +-
  2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/s390/kernel/crash_dump.c b/arch/s390/kernel/crash_dump.c
index cca1827d3d2e..fbc5de66d03b 100644
--- a/arch/s390/kernel/crash_dump.c
+++ b/arch/s390/kernel/crash_dump.c
@@ -609,7 +609,7 @@ int elfcorehdr_alloc(unsigned long long *addr, unsigned long long *size)
  	u64 hdr_off;

  	/* If we are not in kdump or zfcp/nvme dump mode return */
-	if (!oldmem_data.start && !is_ipl_type_dump())
+	if (!dump_available())
  		return 0;
  	/* If we cannot get HSA size for zfcp/nvme dump return error */
  	if (is_ipl_type_dump() && !sclp.hsa_size)
diff --git a/arch/s390/kernel/os_info.c b/arch/s390/kernel/os_info.c
index b695f980bbde..09578f400ef7 100644
--- a/arch/s390/kernel/os_info.c
+++ b/arch/s390/kernel/os_info.c
@@ -148,7 +148,7 @@ static void os_info_old_init(void)

  	if (os_info_init)
  		return;
-	if (!oldmem_data.start && !is_ipl_type_dump())
+	if (!dump_available())
  		goto fail;
  	if (copy_oldmem_kernel(&addr, __LC_OS_INFO, sizeof(addr)))
  		goto fail;
-- 
2.46.1

It looks like we create /proc/vmcore, allocating the elfcorehdr essentially
if dump_available() && (!is_ipl_type_dump() || !sclp.hsa_size).

So in the condition, we would have previously made is_kdump_kernel() happt *after* the
fs init calls.

So I'm wondering if is_kdump_kernel() should simply translate to dump_available(). It
doesn't sound completely right to create /proc/vmcore for "standard zfcp/nvme dump",
but that is what we currently do.

I would have thought we have that special zcore thingy for that.

So I think we should either have

bool is_kdump_kernel(void)
{
	return dump_available();
}

Or

bool is_kdump_kernel(void)
{
	return dump_available() && (!is_ipl_type_dump() || !sclp.hsa_size);
}

I'd prefer the first version.

-- 
Cheers,

David / dhildenb