[Crash-utility] Re: [PATCH] get vmalloc start address from vmcoreinfo

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On 01/03/24 12:32 pm, Aditya Gupta wrote:
Below error is noticed when running crash on vmcore collected from a linux-next
kernel crash (linux-next tag next-20240121):

     # crash /boot/vmlinuz-6.8.0-rc5-next-20240221 ./vmcore
     ……
     ……
     For help, type “help”.
     Type "apropos word" to search for commands related to "word"...

     crash: page excluded: kernel virtual address: c00000000219a2c0  type: “vmlist"

This occured since getting the vmalloc area base address doesn't work in
crash now, due to 'vmap_area_list' being removed in the linux kernel with
below commit (in linux-next tree):

     commit 378eb24a0658dd922b29524e0ce35c6c43f56cba
          mm/vmalloc: remove vmap_area_list

As an alternative, the commit introduced 'VMALLOC_START' in vmcoreinfo to
get base address of vmalloc area, use it to return vmallow start address
instead of depending on vmap_area_list and vmlist


LGTM.

Acked-by: Hari Bathini <hbathini@xxxxxxxxxxxxx>

Reported-by: Sachin Sant <sachinp@xxxxxxxxxxxxx>
Signed-off-by: Aditya Gupta <adityag@xxxxxxxxxxxxx>
---
  memory.c | 11 ++++++++++-
  1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/memory.c b/memory.c
index b84e974a3325..b3027bd101cd 100644
--- a/memory.c
+++ b/memory.c
@@ -17220,11 +17220,20 @@ first_vmalloc_address(void)
  {
  	static ulong vmalloc_start = 0;
          ulong vm_struct, vmap_area;
+	char *vmalloc_start_string;
if (DUMPFILE() && vmalloc_start)
  		return vmalloc_start;
- if (vt->flags & USE_VMAP_AREA) {
+	/*
+	 * 'vmap_area_list' and 'vmlist' in newer kernels might be empty, prefer
+	 * `VMALLOC_START` if exported in vmcoreinfo
+	 */
+	vmalloc_start_string = pc->read_vmcoreinfo("NUMBER(VMALLOC_START)");
+	if (vmalloc_start_string) {
+		vmalloc_start = stol(vmalloc_start_string, QUIET, NULL);
+		free(vmalloc_start_string);
+	} else if (vt->flags & USE_VMAP_AREA) {
  		get_symbol_data("vmap_area_list", sizeof(void *), &vmap_area);
  		if (!vmap_area)
  			return 0;
--
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