Re: [PATCH RESEND v1 2/5] crash: let arch decide crash memory export to iomem_resource

[Sourabh Jain]

Hello Baoquan

On 08/01/25 16:55, Baoquan he wrote:
> Hi,
>
> On 01/08/25 at 03:44pm, Sourabh Jain wrote:
> > insert_crashkernel_resources() adds crash memory to iomem_resource if
> > generic crashkernel reservation is enabled on an architecture.
> >
> > On PowerPC, system RAM is added to iomem_resource. See commit
> > c40dd2f766440 ("powerpc: Add System RAM to /proc/iomem").
> >
> > Enabling generic crashkernel reservation on PowerPC leads to a conflict
> > when system RAM is added to iomem_resource because a part of the system
> > RAM, the crashkernel memory, has already been added to iomem_resource.
> >
> > The next commit in the series "powerpc/crash: use generic crashkernel
> > reservation" enables generic crashkernel reservation on PowerPC. If the
> > crashkernel is added to iomem_resource, the kernel fails to add
> > system RAM to /proc/iomem and prints the following traces:
> >
> > CPU: 0 UID: 0 PID: 1 Comm: swapper/0 Not tainted 6.13.0-rc2+
> > snip...
> > NIP [c000000002016b3c] add_system_ram_resources+0xf0/0x15c
> > LR [c000000002016b34] add_system_ram_resources+0xe8/0x15c
> > Call Trace:
> > [c00000000484bbc0] [c000000002016b34] add_system_ram_resources+0xe8/0x15c
> > [c00000000484bc20] [c000000000010a4c] do_one_initcall+0x7c/0x39c
> > [c00000000484bd00] [c000000002005418] do_initcalls+0x144/0x18c
> > [c00000000484bd90] [c000000002005714] kernel_init_freeable+0x21c/0x290
> > [c00000000484bdf0] [c0000000000110f4] kernel_init+0x2c/0x1b8
> > [c00000000484be50] [c00000000000dd3c] ret_from_kernel_user_thread+0x14/0x1c
> >
> > To avoid this, an architecture hook is added in
> > insert_crashkernel_resources(), allowing the architecture to decide
> > whether crashkernel memory should be added to iomem_resource.
> Have you tried defining HAVE_ARCH_ADD_CRASH_RES_TO_IOMEM_EARLY in ppc to
> add crashkernel region to iomem early?


I didn’t try, but I think even if I do, the kernel will run into the 
same issue
because as soon as crashkernel is added to iomem, there will be a resource
conflict when the PowerPC code tries to add system RAM to iomem. Which
happens during subsys_initcall.

Regardless, I will give it a try.

> Now there are two branches in the
> existing code, adding a hook will make three ways.

I agree. I can try updating powerpc code to not consider crashkernel 
memory as
iomem conflict.

Thanks for the review.

- Sourabh Jain