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

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);