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

[David Hildenbrand]

On 15.10.24 10:41, 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 A right, I remember that there was some outdated documentation.
> > >
> > > > Are you willing to do that, or should I provide an addon patch?
> > >
> > > I can squash the following:
> > >
> > > diff --git a/arch/s390/kernel/smp.c b/arch/s390/kernel/smp.c
> > > index 4df56fdb2488..a4f538876462 100644
> > > --- a/arch/s390/kernel/smp.c
> > > +++ b/arch/s390/kernel/smp.c
> > > @@ -587,16 +587,16 @@ int smp_store_status(int cpu)
> > >     *    with sigp stop-and-store-status. The firmware or the boot-loader
> > >     *    stored the registers of the boot CPU in the absolute lowcore in the
> > >     *    memory of the old system.
> > > - * 3) kdump and the old kernel did not store the CPU state,
> > > - *    or stand-alone kdump for DASD
> > > - *    condition: OLDMEM_BASE != NULL && !is_kdump_kernel()
> > > + * 3) kdump or stand-alone kdump for DASD
> > > + *    condition: OLDMEM_BASE != NULL && !is_ipl_type_dump() == false
> > >     *    The state for all CPUs except the boot CPU needs to be collected
> > >     *    with sigp stop-and-store-status. The kexec code or the boot-loader
> > >     *    stored the registers of the boot CPU in the memory of the old system.
> > > - * 4) kdump and the old kernel stored the CPU state
> > > - *    condition: OLDMEM_BASE != NULL && is_kdump_kernel()
> > > - *    This case does not exist for s390 anymore, setup_arch explicitly
> > > - *    deactivates the elfcorehdr= kernel parameter
> > > + *
> > > + * Note that the old Kdump mode where the old kernel stored the CPU state
> >
> > To be consistent with the rest of the comment, please write kdump in
> > all lower case characters, please.
>
> It obviously was too late in the evening for me :) Thanks!
>
> > > + * does no longer exist: setup_arch explicitly deactivates the elfcorehdr=
> > > + * kernel parameter. The is_kudmp_kernel() implementation on s390 is independent
> >
> > Typo: kudmp.
> >
> > > Does that sound reasonable? I'm not so sure about the "2) stand-alone kdump for
> > > SCSI/NVMe (zfcp/nvme dump with swapped memory)": is that really "kdump" ?
> >
> > Yes, it is some sort of kdump, even though a bit odd.
>
> 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.

I think we can do some follow up cleanups, assuming is_kdump_kernel() here is correct:

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;
diff --git a/drivers/s390/char/zcore.c b/drivers/s390/char/zcore.c
index 33cebb91b933..6a194b4f6ba5 100644
--- a/drivers/s390/char/zcore.c
+++ b/drivers/s390/char/zcore.c
@@ -300,9 +300,7 @@ static int __init zcore_init(void)
        unsigned char arch;
        int rc;
 
-       if (!is_ipl_type_dump())
-               return -ENODATA;
-       if (oldmem_data.start)
+       if (is_kdump_kernel())
                return -ENODATA;
 
        zcore_dbf = debug_register("zcore", 4, 1, 4 * sizeof(long));


--
Cheers,

David / dhildenb