[PATCH v6 04/10] crash_core: serialize crash header preparation against hotplug

[Wandun Chen <chenwandun1@gmail.com>]

From: Wandun Chen <chenwandun@lixiang.com>

crash_prepare_headers() counts memory ranges before populating the
allocated crash_mem array. The weak implementation used by ARM64,
RISC-V and LoongArch walks memblock.memory, while x86 performs the same
two-pass operation over system RAM resources. Concurrent memory hotplug
can change range source between the two walks and make the populate
pass overflow cmem->ranges.

Take device_hotplug_lock when preparing crash headers during
kexec_file_load(). The x86 memory hotplug path already takes
device_hotplug_lock, so call __crash_prepare_headers() directly
to avoid recursive locking.

Sashiko reported this issue in [1].

Fixes: 3751e728cef2 ("arm64: kexec_file: add crash dump support")
Fixes: 1bcca8620a91 ("LoongArch: Add crash dump support for kexec_file")
Fixes: 8acea455fafa ("RISC-V: Support for kexec_file on panic")
Fixes: dd5f726076cc ("kexec: support for kexec on panic using new system call")
Signed-off-by: Wandun Chen <chenwandun@lixiang.com>
Link: https://sashiko.dev/#/message/20260806101002.1F84E1F000E9@smtp.kernel.org [1]
---
 arch/x86/kernel/crash.c    |  2 +-
 include/linux/crash_core.h |  2 ++
 kernel/crash_core.c        | 17 +++++++++++++++--
 3 files changed, 18 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
index e681ec9cf1dc..284d78bc3fd0 100644
--- a/arch/x86/kernel/crash.c
+++ b/arch/x86/kernel/crash.c
@@ -465,7 +465,7 @@ void arch_crash_handle_hotplug_event(struct kimage *image, void *arg)
 	 * Create the new elfcorehdr reflecting the changes to CPU and/or
 	 * memory resources.
 	 */
-	if (crash_prepare_headers(IS_ENABLED(CONFIG_X86_64), &elfbuf, &elfsz, NULL)) {
+	if (__crash_prepare_headers(IS_ENABLED(CONFIG_X86_64), &elfbuf, &elfsz, NULL)) {
 		pr_err("unable to create new elfcorehdr");
 		goto out;
 	}
diff --git a/include/linux/crash_core.h b/include/linux/crash_core.h
index bc087124cd78..28e7a81cf263 100644
--- a/include/linux/crash_core.h
+++ b/include/linux/crash_core.h
@@ -61,6 +61,8 @@ extern int crash_prepare_elf64_headers(struct crash_mem *mem, int need_kernel_ma
 				       void **addr, unsigned long *sz);
 extern int crash_prepare_headers(int need_kernel_map, void **addr,
 				 unsigned long *sz, unsigned long *nr_mem_ranges);
+int __crash_prepare_headers(int need_kernel_map, void **addr, unsigned long *sz,
+			    unsigned long *nr_mem_ranges);
 extern int crash_exclude_core_ranges(struct crash_mem **cmem);
 
 struct kimage;
diff --git a/kernel/crash_core.c b/kernel/crash_core.c
index 77285ae3ce60..3adee1ae120c 100644
--- a/kernel/crash_core.c
+++ b/kernel/crash_core.c
@@ -16,6 +16,7 @@
 #include <linux/mm.h>
 #include <linux/cpuhotplug.h>
 #include <linux/memblock.h>
+#include <linux/device.h>
 #include <linux/kmemleak.h>
 #include <linux/crash_core.h>
 #include <linux/reboot.h>
@@ -338,8 +339,8 @@ int crash_exclude_core_ranges(struct crash_mem **cmem)
 	return 0;
 }
 
-int crash_prepare_headers(int need_kernel_map, void **addr, unsigned long *sz,
-			  unsigned long *nr_mem_ranges)
+int __crash_prepare_headers(int need_kernel_map, void **addr, unsigned long *sz,
+			    unsigned long *nr_mem_ranges)
 {
 	unsigned int max_nr_ranges;
 	struct crash_mem *cmem;
@@ -376,6 +377,18 @@ int crash_prepare_headers(int need_kernel_map, void **addr, unsigned long *sz,
 	return ret;
 }
 
+int crash_prepare_headers(int need_kernel_map, void **addr, unsigned long *sz,
+			  unsigned long *nr_mem_ranges)
+{
+	int ret;
+
+	lock_device_hotplug();
+	ret = __crash_prepare_headers(need_kernel_map, addr, sz, nr_mem_ranges);
+	unlock_device_hotplug();
+
+	return ret;
+}
+
 /**
  * crash_exclude_mem_range - exclude a mem range for existing ranges
  * @mem: mem->range contains an array of ranges sorted in ascending order
-- 
2.43.0