On 20.11.24 11:13, Baoquan He wrote:
On 10/25/24 at 05:11pm, David Hildenbrand wrote:
s390 allocates+prepares the elfcore hdr in the dump (2nd) kernel, not in
the crashed kernel.
RAM provided by memory devices such as virtio-mem can only be detected
using the device driver; when vmcore_init() is called, these device
drivers are usually not loaded yet, or the devices did not get probed
yet. Consequently, on s390 these RAM ranges will not be included in
the crash dump, which makes the dump partially corrupt and is
unfortunate.
Instead of deferring the vmcore_init() call, to an (unclear?) later point,
let's reuse the vmcore_cb infrastructure to obtain device RAM ranges as
the device drivers probe the device and get access to this information.
Then, we'll add these ranges to the vmcore, adding more PT_LOAD
entries and updating the offsets+vmcore size.
Use Kconfig tricks to include this code automatically only if (a) there is
a device driver compiled that implements the callback
(PROVIDE_PROC_VMCORE_DEVICE_RAM) and; (b) the architecture actually needs
this information (NEED_PROC_VMCORE_DEVICE_RAM).
The current target use case is s390, which only creates an elf64
elfcore, so focusing on elf64 is sufficient.
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
---
fs/proc/Kconfig | 25 ++++++
fs/proc/vmcore.c | 156 +++++++++++++++++++++++++++++++++++++
include/linux/crash_dump.h | 9 +++
3 files changed, 190 insertions(+)
diff --git a/fs/proc/Kconfig b/fs/proc/Kconfig
index d80a1431ef7b..1e11de5f9380 100644
--- a/fs/proc/Kconfig
+++ b/fs/proc/Kconfig
@@ -61,6 +61,31 @@ config PROC_VMCORE_DEVICE_DUMP
as ELF notes to /proc/vmcore. You can still disable device
dump using the kernel command line option 'novmcoredd'.
+config PROVIDE_PROC_VMCORE_DEVICE_RAM
+ def_bool n
+
+config NEED_PROC_VMCORE_DEVICE_RAM
+ def_bool n
+
+config PROC_VMCORE_DEVICE_RAM
+ def_bool y
+ depends on PROC_VMCORE
+ depends on NEED_PROC_VMCORE_DEVICE_RAM
+ depends on PROVIDE_PROC_VMCORE_DEVICE_RAM
Kconfig item is always a thing I need learn to master.
Yes, it's usually a struggle to get it right. It took me a couple of
iterations to get to this point :)
When I checked
this part, I have to write them down to deliberate. I am wondering if
below 'simple version' works too and more understandable. Please help
point out what I have missed.
===========simple version======
config PROC_VMCORE_DEVICE_RAM
def_bool y
depends on PROC_VMCORE && VIRTIO_MEM
depends on NEED_PROC_VMCORE_DEVICE_RAM
config S390
select NEED_PROC_VMCORE_DEVICE_RAM
> ============
So the three changes you did are
(a) Remove the config option but select/depend on them.
(b) Remove the "depends on PROC_VMCORE" from PROC_VMCORE_DEVICE_RAM,
and the "if PROC_VMCORE" from s390.
(c) Remove the PROVIDE_PROC_VMCORE_DEVICE_RAM
Regarding (a), that doesn't work. If you select a config option that
doesn't exist, it is silently dropped. It's always treated as if it
wouldn't be set.
Regarding (b), I think that's an anti-pattern (having config options
enabled that are completely ineffective) and I don't see a benefit
dropping them.
Regarding (c), it would mean that s390x unconditionally includes that
code even if virtio-mem is not configured in.
So while we could drop PROVIDE_PROC_VMCORE_DEVICE_RAM -- (c), it would
that we end up including code in configurations that don't possibly need
it. That's why I included that part.
======= config items extracted from this patchset====
config PROVIDE_PROC_VMCORE_DEVICE_RAM
def_bool n
config NEED_PROC_VMCORE_DEVICE_RAM
def_bool n
config PROC_VMCORE_DEVICE_RAM
def_bool y
depends on PROC_VMCORE
depends on NEED_PROC_VMCORE_DEVICE_RAM
depends on PROVIDE_PROC_VMCORE_DEVICE_RAM
config VIRTIO_MEM
depends on X86_64 || ARM64 || RISCV
~~~~~ I don't get why VIRTIO_MEM dones't depend on S390 if
s390 need PROC_VMCORE_DEVICE_RAM.
This series depends on s390 support for virtio-mem, which just went
upstream.
See
commit 38968bcdcc1d46f2fdcd3a72599d5193bf8baf84
Author: David Hildenbrand <david@xxxxxxxxxx>
Date: Fri Oct 25 16:14:49 2024 +0200
virtio-mem: s390 support
......
select PROVIDE_PROC_VMCORE_DEVICE_RAM if PROC_VMCORE
config S390
select NEED_PROC_VMCORE_DEVICE_RAM if PROC_VMCORE
=================================================
Thanks for having a look!
--
Cheers,
David / dhildenb
