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Subject[PATCH] coredump_filter: add hugepage dumping v4
Date
Hi Kawai-san,

Thanks!


> This should be:
> write 0x21 to the process's proc file.
>
> Except for this, it seems OK. Thanks.
>
> Reviewed-by: Hidehiro Kawai <hidehiro.kawai.ez@hitachi.com>
>
> > - $ echo 0x1 > /proc/1234/coredump_filter
> > + $ echo 0x21 > /proc/1234/coredump_filter
> >
> > When a new process is created, the process inherits the bitmask status from its
> > parent. It is useful to set up coredump_filter before the program runs.

new version is attached.



============================================
From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Subject: [PATCH v4] coredump_filter: add hugepage core dumping

Changelog
-----------------
v3 -> v4
- fixed documentation typo.

v2 -> v3
- separated /proc/[pid]/core_dump_filter bits into
shared and private mapping pages.
- updated document

v1 -> v2
- updated document



Now, hugepage's vma has VM_RESERVED flag in order not to being swapped.
But VM_RESERVED vma isn't core dumped because this flag is often used for
some kernel vmas (e.g. vmalloc, sound related).

Then hugepage is never dumped and it can't be debugged easily.
Many developers want hugepages to be included into core-dump.

However, We can't read generic VM_RESERVED area because this area is often
IO mapping area.
then these area reading may change device state. it is definitly undesiable
side-effect.

So, To add hugepage specific bit of the coredump filter is better.
it will be able to hugepage core dumping and doesn't cause any side-effect
to any i/o devices.

In additional, libhugetlb use hugetlb private mapping pages as anonymous page.
Then, hugepage private mapping pages should be core dumped by default.


Then, /proc/[pid]/core_dump_filter has two new bits.

- bit 5 mean hugetlb private mapping pages are dumped or not. (default: yes)
- bit 6 mean hugetlb shared mapping pages are dumped or not. (default: no)


I tested by following method.

% ulimit -c unlimited
% ./crash_hugepage 50
% ./crash_hugepage 50 -p
% ls -lh
% gdb ./crash_hugepage core
%
% echo 0x43 > /proc/self/coredump_filter
% ./crash_hugepage 50
% ./crash_hugepage 50 -p
% ls -lh
% gdb ./crash_hugepage core

crash_hugepage.c
------------------------------------------------
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <sys/mman.h>
#include <string.h>

#include "hugetlbfs.h"

int main(int argc, char** argv){
char* p;
int ch;
int mmap_flags = MAP_SHARED;
int fd;
int nr_pages;

while((ch = getopt(argc, argv, "p")) != -1) {
switch (ch) {
case 'p':
mmap_flags &= ~MAP_SHARED;
mmap_flags |= MAP_PRIVATE;
break;
default:
/* nothing*/
break;
}
}
argc -= optind;
argv += optind;

if (argc == 0){
printf("need # of pages\n");
exit(1);
}

nr_pages = atoi(argv[0]);
if (nr_pages < 2) {
printf("nr_pages must >2\n");
exit(1);
}

fd = hugetlbfs_unlinked_fd();
p = mmap(NULL, nr_pages * gethugepagesize(),
PROT_READ|PROT_WRITE, mmap_flags, fd, 0);

sleep(2);

*(p + gethugepagesize()) = 1; /* COW */
sleep(2);

/* crash! */
*(int*)0 = 1;

return 0;
}

-----------------------------------------------------


Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Reviewed-by: Kawai Hidehiro <hidehiro.kawai.ez@hitachi.com>
CC: Hugh Dickins <hugh@veritas.com>
CC: William Irwin <wli@holomorphy.com>
CC: Adam Litke <agl@us.ibm.com>

---
Documentation/filesystems/proc.txt | 15 ++++++++++-----
fs/binfmt_elf.c | 12 ++++++++++--
include/linux/sched.h | 7 +++++--
3 files changed, 25 insertions(+), 9 deletions(-)

Index: b/Documentation/filesystems/proc.txt
===================================================================
--- a/Documentation/filesystems/proc.txt 2008-09-25 21:19:13.000000000 +0900
+++ b/Documentation/filesystems/proc.txt 2008-09-25 21:21:05.000000000 +0900
@@ -2408,24 +2408,29 @@ will be dumped when the <pid> process is
of memory types. If a bit of the bitmask is set, memory segments of the
corresponding memory type are dumped, otherwise they are not dumped.

-The following 4 memory types are supported:
+The following 7 memory types are supported:
- (bit 0) anonymous private memory
- (bit 1) anonymous shared memory
- (bit 2) file-backed private memory
- (bit 3) file-backed shared memory
- (bit 4) ELF header pages in file-backed private memory areas (it is
effective only if the bit 2 is cleared)
+ - (bit 5) hugetlb private memory
+ - (bit 6) hugetlb shared memory

Note that MMIO pages such as frame buffer are never dumped and vDSO pages
are always dumped regardless of the bitmask status.

-Default value of coredump_filter is 0x3; this means all anonymous memory
-segments are dumped.
+ Note bit 0-4 doesn't effect any hugetlb memory. hugetlb memory are only
+ effected by bit 5-6.
+
+Default value of coredump_filter is 0x23; this means all anonymous memory
+segments and hugetlb private memory are dumped.

If you don't want to dump all shared memory segments attached to pid 1234,
-write 1 to the process's proc file.
+write 0x21 to the process's proc file.

- $ echo 0x1 > /proc/1234/coredump_filter
+ $ echo 0x21 > /proc/1234/coredump_filter

When a new process is created, the process inherits the bitmask status from its
parent. It is useful to set up coredump_filter before the program runs.
Index: b/fs/binfmt_elf.c
===================================================================
--- a/fs/binfmt_elf.c 2008-09-25 21:18:58.000000000 +0900
+++ b/fs/binfmt_elf.c 2008-09-25 21:19:16.000000000 +0900
@@ -1156,16 +1156,24 @@ static int dump_seek(struct file *file,
static unsigned long vma_dump_size(struct vm_area_struct *vma,
unsigned long mm_flags)
{
+#define FILTER(type) (mm_flags & (1UL << MMF_DUMP_##type))
+
/* The vma can be set up to tell us the answer directly. */
if (vma->vm_flags & VM_ALWAYSDUMP)
goto whole;

+ /* Hugetlb memory check */
+ if (vma->vm_flags & VM_HUGETLB) {
+ if ((vma->vm_flags & VM_SHARED) && FILTER(HUGETLB_SHARED))
+ goto whole;
+ if (!(vma->vm_flags & VM_SHARED) && FILTER(HUGETLB_PRIVATE))
+ goto whole;
+ }
+
/* Do not dump I/O mapped devices or special mappings */
if (vma->vm_flags & (VM_IO | VM_RESERVED))
return 0;

-#define FILTER(type) (mm_flags & (1UL << MMF_DUMP_##type))
-
/* By default, dump shared memory if mapped from an anonymous file. */
if (vma->vm_flags & VM_SHARED) {
if (vma->vm_file->f_path.dentry->d_inode->i_nlink == 0 ?
Index: b/include/linux/sched.h
===================================================================
--- a/include/linux/sched.h 2008-09-25 21:18:58.000000000 +0900
+++ b/include/linux/sched.h 2008-09-25 21:19:16.000000000 +0900
@@ -403,12 +403,15 @@ extern int get_dumpable(struct mm_struct
#define MMF_DUMP_MAPPED_PRIVATE 4
#define MMF_DUMP_MAPPED_SHARED 5
#define MMF_DUMP_ELF_HEADERS 6
+#define MMF_DUMP_HUGETLB_PRIVATE 7
+#define MMF_DUMP_HUGETLB_SHARED 8
#define MMF_DUMP_FILTER_SHIFT MMF_DUMPABLE_BITS
-#define MMF_DUMP_FILTER_BITS 5
+#define MMF_DUMP_FILTER_BITS 7
#define MMF_DUMP_FILTER_MASK \
(((1 << MMF_DUMP_FILTER_BITS) - 1) << MMF_DUMP_FILTER_SHIFT)
#define MMF_DUMP_FILTER_DEFAULT \
- ((1 << MMF_DUMP_ANON_PRIVATE) | (1 << MMF_DUMP_ANON_SHARED))
+ ((1 << MMF_DUMP_ANON_PRIVATE) | (1 << MMF_DUMP_ANON_SHARED) |\
+ (1 << MMF_DUMP_HUGETLB_PRIVATE))

struct sighand_struct {
atomic_t count;



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