Re: [PATCH v2 1/7] s390/kdump: implement is_kdump_kernel()

[David Hildenbrand]

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 A right, I remember that there was some outdated documentation.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@xxxxxxxxxx/

With the following cleanup in mind:

From 9fbbff43f725a8482ce9e85857316ab8484ff3c8 Mon Sep 17 00:00:00 2001
From: David Hildenbrand <david@xxxxxxxxxx>
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@xxxxxxxxxx>
---
 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