Re: FAILED: patch "[PATCH] crash: fix crashkernel resource shrink" failed to apply to 6.6-stable tree

[Sourabh Jain <sourabhjain@linux.ibm.com>]

Hello Greg

On 20/11/25 21:45, gregkh@linuxfoundation.org wrote:
> The patch below does not apply to the 6.6-stable tree.
> If someone wants it applied there, or to any other stable or longterm
> tree, then please email the backport, including the original git commit
> id to <stable@vger.kernel.org>.
>
> To reproduce the conflict and resubmit, you may use the following commands:
>
> git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.6.y
> git checkout FETCH_HEAD
> git cherry-pick -x 00fbff75c5acb4755f06f08bd1071879c63940c5
> # <resolve conflicts, build, test, etc.>
> git commit -s

I followed the above steps and back-ported the fix.

> git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2025112029-arrogance-bondless-6a5b@gregkh' --subject-prefix 'PATCH 6.6.y' HEAD^..

I used the above command to send the back-ported patch. The command ran
fine, but I do not see my back-ported patch on lore.kernel.org.

This is the first time I am sending a patch using --in-reply, so I am not
sure how it works. Please let me know if you did not receive the
backported patch.

I also kept the Signed-off-by and Acked-by tags in the backported patch,
as it is identical to the original patch.

Thanks,
Sourabh Jain

>
> Possible dependencies:
>
>
>
> thanks,
>
> greg k-h
>
> ------------------ original commit in Linus's tree ------------------
>
>  From 00fbff75c5acb4755f06f08bd1071879c63940c5 Mon Sep 17 00:00:00 2001
> From: Sourabh Jain <sourabhjain@linux.ibm.com>
> Date: Sun, 2 Nov 2025 01:07:41 +0530
> Subject: [PATCH] crash: fix crashkernel resource shrink
>
> When crashkernel is configured with a high reservation, shrinking its
> value below the low crashkernel reservation causes two issues:
>
> 1. Invalid crashkernel resource objects
> 2. Kernel crash if crashkernel shrinking is done twice
>
> For example, with crashkernel=200M,high, the kernel reserves 200MB of high
> memory and some default low memory (say 256MB).  The reservation appears
> as:
>
> cat /proc/iomem | grep -i crash
> af000000-beffffff : Crash kernel
> 433000000-43f7fffff : Crash kernel
>
> If crashkernel is then shrunk to 50MB (echo 52428800 >
> /sys/kernel/kexec_crash_size), /proc/iomem still shows 256MB reserved:
> af000000-beffffff : Crash kernel
>
> Instead, it should show 50MB:
> af000000-b21fffff : Crash kernel
>
> Further shrinking crashkernel to 40MB causes a kernel crash with the
> following trace (x86):
>
> BUG: kernel NULL pointer dereference, address: 0000000000000038
> PGD 0 P4D 0
> Oops: 0000 [#1] PREEMPT SMP NOPTI
> <snip...>
> Call Trace: <TASK>
> ? __die_body.cold+0x19/0x27
> ? page_fault_oops+0x15a/0x2f0
> ? search_module_extables+0x19/0x60
> ? search_bpf_extables+0x5f/0x80
> ? exc_page_fault+0x7e/0x180
> ? asm_exc_page_fault+0x26/0x30
> ? __release_resource+0xd/0xb0
> release_resource+0x26/0x40
> __crash_shrink_memory+0xe5/0x110
> crash_shrink_memory+0x12a/0x190
> kexec_crash_size_store+0x41/0x80
> kernfs_fop_write_iter+0x141/0x1f0
> vfs_write+0x294/0x460
> ksys_write+0x6d/0xf0
> <snip...>
>
> This happens because __crash_shrink_memory()/kernel/crash_core.c
> incorrectly updates the crashk_res resource object even when
> crashk_low_res should be updated.
>
> Fix this by ensuring the correct crashkernel resource object is updated
> when shrinking crashkernel memory.
>
> Link: https://lkml.kernel.org/r/20251101193741.289252-1-sourabhjain@linux.ibm.com
> Fixes: 16c6006af4d4 ("kexec: enable kexec_crash_size to support two crash kernel regions")
> Signed-off-by: Sourabh Jain <sourabhjain@linux.ibm.com>
> Acked-by: Baoquan He <bhe@redhat.com>
> Cc: Zhen Lei <thunder.leizhen@huawei.com>
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
>
> diff --git a/kernel/crash_core.c b/kernel/crash_core.c
> index 3b1c43382eec..99dac1aa972a 100644
> --- a/kernel/crash_core.c
> +++ b/kernel/crash_core.c
> @@ -373,7 +373,7 @@ static int __crash_shrink_memory(struct resource *old_res,
>   		old_res->start = 0;
>   		old_res->end   = 0;
>   	} else {
> -		crashk_res.end = ram_res->start - 1;
> +		old_res->end = ram_res->start - 1;
>   	}
>   
>   	crash_free_reserved_phys_range(ram_res->start, ram_res->end);
>