Re: [PATCH] makedumpfile: call initial before use cache

["HAGIO KAZUHITO(萩尾 一仁)" <k-hagio-ab@nec.com>]

On 2024/07/20 16:38, Lichen Liu wrote:

>> This will work only for 4.19 and later kernels, but might reduce users
>> that hit the issue.  Does this work for you?
> That works for me because I'm testing for the 6.x kernel.

Thanks for the check.  Is the issue a segmentation fault?
I've made a patch below, is this OK?


 From 084742cba5b81da563074454ab8c879e8e411cb0 Mon Sep 17 00:00:00 2001
From: Kazuhito Hagio <k-hagio-ab@nec.com>
Date: Mon, 22 Jul 2024 14:31:43 +0900
Subject: [PATCH] Workaround for segfault by "makedumpfile --mem-usage" on PPC64

"makedumpfile --mem-usage /proc/kcore" can cause a segmentation fault on
PPC64, because the readmem() of the following code path uses cache
before it's initialized in initial().

   show_mem_usage
     get_page_offset
       get_versiondep_info_ppc64
         readmem
     ...
     initial
         cache_init

The get_page_offset() is needed to get vmcoreinfo from /proc/kcore data,
so we can avoid calling it when a vmcoreinfo exists in the ELF NOTE
segment of /proc/kcore, i.e. on Linux 4.19 and later.

(Note: for older kernels, we will need another way to fix it.)

Reported-by: Lichen Liu <lichliu@redhat.com>
Signed-off-by: Kazuhito Hagio <k-hagio-ab@nec.com>
---
  makedumpfile.c | 12 ++++++------
  1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/makedumpfile.c b/makedumpfile.c
index 5b347126db76..7d1dfcca50d8 100644
--- a/makedumpfile.c
+++ b/makedumpfile.c
@@ -12019,14 +12019,14 @@ int show_mem_usage(void)
  		DEBUG_MSG("Read vmcoreinfo from NOTE segment: %d\n", vmcoreinfo);
  	}
  
-	if (!get_page_offset())
-		return FALSE;
+	if (!vmcoreinfo) {
+		if (!get_page_offset())
+			return FALSE;
  
-	/* paddr_to_vaddr() on arm64 needs phys_base. */
-	if (!get_phys_base())
-		return FALSE;
+		/* paddr_to_vaddr() on arm64 needs phys_base. */
+		if (!get_phys_base())
+			return FALSE;
  
-	if (!vmcoreinfo) {
  		if (!get_sys_kernel_vmcoreinfo(&vmcoreinfo_addr, &vmcoreinfo_len))
  			return FALSE;
  
-- 
2.31.1
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