1:40 a.m.
Since kernel commit cf338283652f ("slab: remove struct kmem_cache_cpu")
in linux-next we have no more 'cpu_slab' member in struct kmem_cache.
Pick 'cpu_sheaves' as an alternative kmem_cache member for kernel-next to
identify the SLUB case.
Without the patch, crash fails to start on kernel-next with the error
message:
crash: invalid structure member offset: kmem_cache_s_num
FILE: memory.c LINE: 9988 FUNCTION: kmem_cache_init()
This fix allows the crash to start with no errors. But kmap -s is no
longer working for kernel-next since kmem_cache_cpu array is completely
missing.
Signed-off-by: Mikhail Zaslonko <zaslonko(a)linux.ibm.com>
---
memory.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/memory.c b/memory.c
index cbc8d2f..3373fdb 100644
--- a/memory.c
+++ b/memory.c
@@ -672,6 +672,7 @@ vm_init(void)
} else if (!VALID_STRUCT(kmem_slab_s) &&
!VALID_STRUCT(slab_s) &&
!MEMBER_EXISTS("kmem_cache", "cpu_slab") &&
+ !MEMBER_EXISTS("kmem_cache", "cpu_sheaves") &&
(VALID_STRUCT(slab) || (vt->flags & SLAB_OVERLOAD_PAGE))) {
vt->flags |= PERCPU_KMALLOC_V2;
@@ -816,7 +817,7 @@ vm_init(void)
if (INVALID_MEMBER(page_first_page))
ANON_MEMBER_OFFSET_INIT(page_first_page, "page", "first_page");
- } else if (MEMBER_EXISTS("kmem_cache", "cpu_slab") &&
+ } else if ((MEMBER_EXISTS("kmem_cache", "cpu_slab") ||
MEMBER_EXISTS("kmem_cache", "cpu_sheaves")) &&
STRUCT_EXISTS("kmem_cache_node")) {
vt->flags |= KMALLOC_SLUB;
--
2.52.0
3:21 a.m.
New subject: [PATCH] memory: Handle crash failure in linux-next caused by struct kmem_cache changes
Hi Mikhail,
Thanks for your fix on this!
On Tue, Jan 27, 2026 at 8:40 PM Mikhail Zaslonko <zaslonko(a)linux.ibm.com> wrote:
Since kernel commit cf338283652f ("slab: remove struct kmem_cache_cpu")
in linux-next we have no more 'cpu_slab' member in struct kmem_cache.
Pick 'cpu_sheaves' as an alternative kmem_cache member for kernel-next to
identify the SLUB case.
Without the patch, crash fails to start on kernel-next with the error
message:
crash: invalid structure member offset: kmem_cache_s_num
FILE: memory.c LINE: 9988 FUNCTION: kmem_cache_init()
This fix allows the crash to start with no errors. But kmap -s is no
longer working for kernel-next since kmem_cache_cpu array is completely
missing.
Signed-off-by: Mikhail Zaslonko <zaslonko(a)linux.ibm.com>
---
memory.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/memory.c b/memory.c
index cbc8d2f..3373fdb 100644
--- a/memory.c
+++ b/memory.c
@@ -672,6 +672,7 @@ vm_init(void)
} else if (!VALID_STRUCT(kmem_slab_s) &&
!VALID_STRUCT(slab_s) &&
!MEMBER_EXISTS("kmem_cache", "cpu_slab")
&&
+ !MEMBER_EXISTS("kmem_cache", "cpu_sheaves")
&&
(VALID_STRUCT(slab) || (vt->flags & SLAB_OVERLOAD_PAGE))) {
vt->flags |= PERCPU_KMALLOC_V2;
@@ -816,7 +817,7 @@ vm_init(void)
if (INVALID_MEMBER(page_first_page))
ANON_MEMBER_OFFSET_INIT(page_first_page, "page",
"first_page");
- } else if (MEMBER_EXISTS("kmem_cache", "cpu_slab")
&&
+ } else if ((MEMBER_EXISTS("kmem_cache", "cpu_slab") ||
MEMBER_EXISTS("kmem_cache", "cpu_sheaves")) &&
STRUCT_EXISTS("kmem_cache_node")) {
vt->flags |= KMALLOC_SLUB;
I tested your patch and find "kmem -s/-S" both not work:
crash> kmem -s
CACHE OBJSIZE ALLOCATED TOTAL SLABS SSIZE NAME
kmem: cannot determine location of kmem_cache.cpu_slab page
crash> kmem -S
CACHE OBJSIZE ALLOCATED TOTAL SLABS SSIZE NAME
kmem: cannot determine location of kmem_cache.cpu_slab page
And I add the following change upon your patch, to 1) let "kmem -s"
work and 2) "kmem -S" output error info.
@@ -5270,6 +5272,9 @@ cmd_kmem(void)
if (sflag || Sflag || rflag || !(vt->flags & KMEM_CACHE_INIT))
kmem_cache_init();
+ if (Sflag && MEMBER_EXISTS("kmem_cache",
"cpu_sheaves"))
+ error(FATAL, "-S not supported for this kernel\n");
+
while (args[optind]) {
if (hexadecimal(args[optind], 0)) {
value[spec_addr++] =
@@ -20401,7 +20406,6 @@ get_cpu_slab_ptr(struct meminfo *si, int cpu,
ulong *cpu_freelist)
default:
cpu_slab_ptr = 0;
- error(FATAL, "cannot determine location of
kmem_cache.cpu_slab page\n");
}
return cpu_slab_ptr;
And from my testing:
crash> kmem -s
CACHE OBJSIZE ALLOCATED TOTAL SLABS SSIZE NAME
ffff8b4e83d5fb00 2120 0 0 0 32k
nfs4_xattr_cache_cache
ffff8b4e83d5f200 216 0 0 0 4k nfs_direct_cache
ffff8b4e83d5fc00 736 28 42 2 16k nfs_commit_data
ffff8b4e83d5f900 936 56 68 4 16k nfs_write_data
...
To contrast with /proc/slabinfo:
nfs4_xattr_cache_cache 0 0 2128 15 8 : tunables 0
0 0 : slabdata 0 0 0
nfs_direct_cache 0 0 216 18 1 : tunables 0 0
0 : slabdata 0 0 0
nfs_commit_data 28 42 768 21 4 : tunables 0 0
0 : slabdata 2 2 0
nfs_write_data 56 68 960 17 4 : tunables 0 0
0 : slabdata 4 4 0
nfs_read_data 0 0 960 17 4 : tunables 0 0
0 : slabdata 0 0 0
The "kmem -s" output looks fine.
crash> kmem -S
kmem: -S not supported for this kernel
What do you think of this?
Thanks,
Tao Liu
--
2.52.0
9:08 a.m.
New subject: [PATCH] memory: Handle crash failure in linux-next caused by struct kmem_cache changes
Hi Tao,
On 11-Feb-26 10:21, Tao Liu wrote:
Hi Mikhail,
Thanks for your fix on this!
On Tue, Jan 27, 2026 at 8:40 PM Mikhail Zaslonko <zaslonko(a)linux.ibm.com> wrote:
>
> Since kernel commit cf338283652f ("slab: remove struct kmem_cache_cpu")
> in linux-next we have no more 'cpu_slab' member in struct kmem_cache.
> Pick 'cpu_sheaves' as an alternative kmem_cache member for kernel-next to
> identify the SLUB case.
>
> Without the patch, crash fails to start on kernel-next with the error
> message:
>
> crash: invalid structure member offset: kmem_cache_s_num
> FILE: memory.c LINE: 9988 FUNCTION: kmem_cache_init()
>
> This fix allows the crash to start with no errors. But kmap -s is no
> longer working for kernel-next since kmem_cache_cpu array is completely
> missing.
>
> Signed-off-by: Mikhail Zaslonko <zaslonko(a)linux.ibm.com>
> ---
> memory.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/memory.c b/memory.c
> index cbc8d2f..3373fdb 100644
> --- a/memory.c
> +++ b/memory.c
> @@ -672,6 +672,7 @@ vm_init(void)
> } else if (!VALID_STRUCT(kmem_slab_s) &&
> !VALID_STRUCT(slab_s) &&
> !MEMBER_EXISTS("kmem_cache", "cpu_slab")
&&
> + !MEMBER_EXISTS("kmem_cache", "cpu_sheaves")
&&
> (VALID_STRUCT(slab) || (vt->flags & SLAB_OVERLOAD_PAGE)))
{
> vt->flags |= PERCPU_KMALLOC_V2;
>
> @@ -816,7 +817,7 @@ vm_init(void)
> if (INVALID_MEMBER(page_first_page))
> ANON_MEMBER_OFFSET_INIT(page_first_page, "page",
"first_page");
>
> - } else if (MEMBER_EXISTS("kmem_cache", "cpu_slab")
&&
> + } else if ((MEMBER_EXISTS("kmem_cache", "cpu_slab") ||
MEMBER_EXISTS("kmem_cache", "cpu_sheaves")) &&
> STRUCT_EXISTS("kmem_cache_node")) {
> vt->flags |= KMALLOC_SLUB;
>
I tested your patch and find "kmem -s/-S" both not work:
crash> kmem -s
CACHE OBJSIZE ALLOCATED TOTAL SLABS SSIZE NAME
kmem: cannot determine location of kmem_cache.cpu_slab page
crash> kmem -S
CACHE OBJSIZE ALLOCATED TOTAL SLABS SSIZE NAME
kmem: cannot determine location of kmem_cache.cpu_slab page
And I add the following change upon your patch, to 1) let "kmem -s"
work and 2) "kmem -S" output error info.
@@ -5270,6 +5272,9 @@ cmd_kmem(void)
if (sflag || Sflag || rflag || !(vt->flags & KMEM_CACHE_INIT))
kmem_cache_init();
+ if (Sflag && MEMBER_EXISTS("kmem_cache",
"cpu_sheaves"))
+ error(FATAL, "-S not supported for this kernel\n");
+
Shouldn't it be:
if (Sflag && !MEMBER_EXISTS("kmem_cache", "cpu_slab"))
Otherwise kmem -S is 'not supported' on all kernels starting 6.18
('cpu_sheaves' belongs to struct kmem_cache since kernel v.6.18)
while (args[optind]) {
if (hexadecimal(args[optind], 0)) {
value[spec_addr++] =
@@ -20401,7 +20406,6 @@ get_cpu_slab_ptr(struct meminfo *si, int cpu,
ulong *cpu_freelist)
default:
cpu_slab_ptr = 0;
- error(FATAL, "cannot determine location of
indeed, 'kmem -s' works again on kernel-next after this trick :)
Thanks,
Tao Liu
> --
> 2.52.0
>
1:08 a.m.
New subject: [PATCH] memory: Handle crash failure in linux-next caused by struct kmem_cache changes
Hi Mikhail,
On Sat, Feb 14, 2026 at 4:09 AM Mikhail Zaslonko <zaslonko(a)linux.ibm.com> wrote:
Hi Tao,
On 11-Feb-26 10:21, Tao Liu wrote:
> Hi Mikhail,
>
> Thanks for your fix on this!
>
> On Tue, Jan 27, 2026 at 8:40 PM Mikhail Zaslonko <zaslonko(a)linux.ibm.com>
wrote:
>>
>> Since kernel commit cf338283652f ("slab: remove struct
kmem_cache_cpu")
>> in linux-next we have no more 'cpu_slab' member in struct kmem_cache.
>> Pick 'cpu_sheaves' as an alternative kmem_cache member for kernel-next
to
>> identify the SLUB case.
>>
>> Without the patch, crash fails to start on kernel-next with the error
>> message:
>>
>> crash: invalid structure member offset: kmem_cache_s_num
>> FILE: memory.c LINE: 9988 FUNCTION: kmem_cache_init()
>>
>> This fix allows the crash to start with no errors. But kmap -s is no
>> longer working for kernel-next since kmem_cache_cpu array is completely
>> missing.
>>
>> Signed-off-by: Mikhail Zaslonko <zaslonko(a)linux.ibm.com>
>> ---
>> memory.c | 3 ++-
>> 1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/memory.c b/memory.c
>> index cbc8d2f..3373fdb 100644
>> --- a/memory.c
>> +++ b/memory.c
>> @@ -672,6 +672,7 @@ vm_init(void)
>> } else if (!VALID_STRUCT(kmem_slab_s) &&
>> !VALID_STRUCT(slab_s) &&
>> !MEMBER_EXISTS("kmem_cache", "cpu_slab")
&&
>> + !MEMBER_EXISTS("kmem_cache",
"cpu_sheaves") &&
>> (VALID_STRUCT(slab) || (vt->flags &
SLAB_OVERLOAD_PAGE))) {
>> vt->flags |= PERCPU_KMALLOC_V2;
>>
>> @@ -816,7 +817,7 @@ vm_init(void)
>> if (INVALID_MEMBER(page_first_page))
>> ANON_MEMBER_OFFSET_INIT(page_first_page,
"page", "first_page");
>>
>> - } else if (MEMBER_EXISTS("kmem_cache", "cpu_slab")
&&
>> + } else if ((MEMBER_EXISTS("kmem_cache", "cpu_slab")
|| MEMBER_EXISTS("kmem_cache", "cpu_sheaves")) &&
>> STRUCT_EXISTS("kmem_cache_node")) {
>> vt->flags |= KMALLOC_SLUB;
>>
>
> I tested your patch and find "kmem -s/-S" both not work:
>
> crash> kmem -s
> CACHE OBJSIZE ALLOCATED TOTAL SLABS SSIZE NAME
> kmem: cannot determine location of kmem_cache.cpu_slab page
> crash> kmem -S
> CACHE OBJSIZE ALLOCATED TOTAL SLABS SSIZE NAME
> kmem: cannot determine location of kmem_cache.cpu_slab page
>
> And I add the following change upon your patch, to 1) let "kmem -s"
> work and 2) "kmem -S" output error info.
>
> @@ -5270,6 +5272,9 @@ cmd_kmem(void)
> if (sflag || Sflag || rflag || !(vt->flags & KMEM_CACHE_INIT))
> kmem_cache_init();
>
> + if (Sflag && MEMBER_EXISTS("kmem_cache",
"cpu_sheaves"))
> + error(FATAL, "-S not supported for this kernel\n");
> +
Shouldn't it be:
if (Sflag && !MEMBER_EXISTS("kmem_cache",
"cpu_slab"))
Otherwise kmem -S is 'not supported' on all kernels starting 6.18
('cpu_sheaves' belongs to struct kmem_cache since kernel v.6.18)
Right. "kmem -S" currently relies on cpu_slab, not cpu_sheaves.
Could you please send v2 for this? I can ack and merge it so
linux-next can work for crash.
Thanks,
Tao Liu
> while (args[optind]) {
> if (hexadecimal(args[optind], 0)) {
> value[spec_addr++] =
> @@ -20401,7 +20406,6 @@ get_cpu_slab_ptr(struct meminfo *si, int cpu,
> ulong *cpu_freelist)
>
> default:
> cpu_slab_ptr = 0;
> - error(FATAL, "cannot determine location of
indeed, 'kmem -s' works again on kernel-next after this trick :)
>
> Thanks,
> Tao Liu
>
>> --
>> 2.52.0
>>
>
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days inactive
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Tao Liu