| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Message-ID: <0ab2cb14-ba8e-4436-b03d-9457137f492a@redhat.com>
Date: Thu, 11 Sep 2025 20:50:40 +0200
From: David Hildenbrand <david@...hat.com>
To: Sumanth Korikkar <sumanthk@...ux.ibm.com>,
Andrew Morton <akpm@...ux-foundation.org>, linux-mm <linux-mm@...ck.org>
Cc: linux-s390@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
Dan Williams <dan.j.williams@...el.com>,
Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
Gerald Schaefer <gerald.schaefer@...ux.ibm.com>,
Heiko Carstens <hca@...ux.ibm.com>, Vasily Gorbik <gor@...ux.ibm.com>,
Alexander Gordeev <agordeev@...ux.ibm.com>
Subject: Re: [PATCH] resource: Improve child resource handling in
release_mem_region_adjustable()
On 11.09.25 16:00, Sumanth Korikkar wrote:
Hi,
> When memory block is removed via try_remove_memory(), it eventually
> reaches release_mem_region_adjustable(). The current implementation
> assumes that when a busy memory resource is split into two, all child
> resources remain in the lower address range.
>
> This simplification causes problems when child resources actually belong
> to the upper split. For example:
>
> * Initial memory layout:
> lsmem
> RANGE SIZE STATE REMOVABLE BLOCK
> 0x0000000000000000-0x00000002ffffffff 12G online yes 0-95
>
> * /proc/iomem
> 00000000-2dfefffff : System RAM
> 158834000-1597b3fff : Kernel code
> 1597b4000-159f50fff : Kernel data
> 15a13c000-15a218fff : Kernel bss
> 2dff00000-2ffefffff : Crash kernel
> 2fff00000-2ffffffff : System RAM
>
> * After offlining and removing range
> 0x150000000-0x157ffffff
> lsmem
> RANGE SIZE STATE REMOVABLE BLOCK
> 0x0000000000000000-0x000000014fffffff 5.3G online yes 0-41
> 0x0000000150000000-0x0000000157ffffff 128M offline 42
> 0x0000000158000000-0x00000002ffffffff 6.6G online yes 43-95
>
First of all
1) How are you triggering this :)
2) Why do you say "and removing the range" when it's still listed in
lsmem output.
lsmem will only list present memory block devices. So if it's still
listed there, nothing was removed. Or is that prior to actually removing it.
Is this some powerpc dlpar use case?
> The iomem resource gets split into two entries, but kernel code, kernel
> data, and kernel bss remain attached to the lower resource [0–5376M]
> instead of the correct upper resource [5504M–12288M].
Yes.
>
> As a result, WARN_ON() triggers in release_mem_region_adjustable()
> ("Usecase: split into two entries - we need a new resource")
> ------------[ cut here ]------------
> WARNING: CPU: 5 PID: 858 at kernel/resource.c:1486
> release_mem_region_adjustable+0x210/0x280
> Modules linked in:
> CPU: 5 UID: 0 PID: 858 Comm: chmem Not tainted 6.17.0-rc2-11707-g2c36aaf3ba4e
> Hardware name: IBM 3906 M04 704 (z/VM 7.3.0)
> Krnl PSW : 0704d00180000000 0000024ec0dae0e4
> (release_mem_region_adjustable+0x214/0x280)
> R:0 T:1 IO:1 EX:1 Key:0 M:1 W:0 P:0 AS:3 CC:1 PM:0 RI:0 EA:3
> Krnl GPRS: 0000000000000000 00000002ffffafc0 fffffffffffffff0 0000000000000000
> 000000014fffffff 0000024ec2257608 0000000000000000 0000024ec2301758
> 0000024ec22680d0 00000000902c9140 0000000150000000 00000002ffffafc0
> 000003ffa61d8d18 0000024ec21fb478 0000024ec0dae014 000001cec194fbb0
> Krnl Code: 0000024ec0dae0d8: af000000 mc 0,0
> 0000024ec0dae0dc: a7f4ffc1 brc 15,0000024ec0dae05e
> #0000024ec0dae0e0: af000000 mc 0,0
> >0000024ec0dae0e4: a5defffd llilh %r13,65533
> 0000024ec0dae0e8: c04000c6064c larl %r4,0000024ec266ed80
> 0000024ec0dae0ee: eb1d400000f8 laa %r1,%r13,0(%r4)
> 0000024ec0dae0f4: 07e0 bcr 14,%r0
> 0000024ec0dae0f6: a7f4ffc0 brc 15,0000024ec0dae076
> Call Trace:
> [<0000024ec0dae0e4>] release_mem_region_adjustable+0x214/0x280
> ([<0000024ec0dadf3c>] release_mem_region_adjustable+0x6c/0x280)
> [<0000024ec10a2130>] try_remove_memory+0x100/0x140
> [<0000024ec10a4052>] __remove_memory+0x22/0x40
> [<0000024ec18890f6>] config_mblock_store+0x326/0x3e0
> [<0000024ec11f7056>] kernfs_fop_write_iter+0x136/0x210
> [<0000024ec1121e86>] vfs_write+0x236/0x3c0
> [<0000024ec11221b8>] ksys_write+0x78/0x110
> [<0000024ec1b6bfbe>] __do_syscall+0x12e/0x350
> [<0000024ec1b782ce>] system_call+0x6e/0x90
> Last Breaking-Event-Address:
> [<0000024ec0dae014>] release_mem_region_adjustable+0x144/0x280
> ---[ end trace 0000000000000000 ]---
>
> Also, resource adjustment doesn't happen and stale resources still cover
> [0-12288M]. Later, memory re-add fails in register_memory_resource()
> with -EBUSY.
>
> i.e: /proc/iomem is still:
> 00000000-2dfefffff : System RAM
> 158834000-1597b3fff : Kernel code
> 1597b4000-159f50fff : Kernel data
> 15a13c000-15a218fff : Kernel bss
> 2dff00000-2ffefffff : Crash kernel
> 2fff00000-2ffffffff : System RAM
>
> Enhance release_mem_region_adjustable() to reassign child resources
> to the correct parent after a split. Children are now assigned based on
> their actual range: If they fall within the lower split, keep them in
> the lower parent. If they fall within the upper split, move them to the
> upper parent.
>
> Kernel code/data/bss regions are not offlined, so they will always
> reside entirely within one parent and never span across both.
Yes.
>
> Output after the enhancement:
> * Initial state /proc/iomem (before removal of memory block):
> 00000000-2dfefffff : System RAM
> 1f94f8000-1fa477fff : Kernel code
> 1fa478000-1fac14fff : Kernel data
> 1fae00000-1faedcfff : Kernel bss
> 2dff00000-2ffefffff : Crash kernel
> 2fff00000-2ffffffff : System RAM
>
> * Offline and remove 0x1e8000000-0x1efffffff memory range
> * /proc/iomem
> 00000000-1e7ffffff : System RAM
> 1f0000000-2dfefffff : System RAM
> 1f94f8000-1fa477fff : Kernel code
> 1fa478000-1fac14fff : Kernel data
> 1fae00000-1faedcfff : Kernel bss
> 2dff00000-2ffefffff : Crash kernel
> 2fff00000-2ffffffff : System RAM
>
Do we need a Fixes: and CC stable?
> Signed-off-by: Sumanth Korikkar <sumanthk@...ux.ibm.com>
> ---
> kernel/resource.c | 44 +++++++++++++++++++++++++++++++++++++++-----
> 1 file changed, 39 insertions(+), 5 deletions(-)
>
> diff --git a/kernel/resource.c b/kernel/resource.c
> index f9bb5481501a..c329b8a4aa2f 100644
> --- a/kernel/resource.c
> +++ b/kernel/resource.c
> @@ -1388,6 +1388,41 @@ void __release_region(struct resource *parent, resource_size_t start,
> EXPORT_SYMBOL(__release_region);
>
> #ifdef CONFIG_MEMORY_HOTREMOVE
> +static void append_child_to_parent(struct resource *new_parent, struct resource *new_child)
> +{
> + struct resource *child;
> +
> + child = new_parent->child;
> + if (child) {
> + while (child->sibling)
> + child = child->sibling;
> + child->sibling = new_child;
Shouldn't we take care of the address ordering here? I guess this works
because we process them in left-to-right (lowest-to-highest) address.
> + } else {
> + new_parent->child = new_child;
> + }
> + new_child->parent = new_parent;
> + new_child->sibling = NULL;
> +}
> +
> +static void move_children_to_parent(struct resource *old_parent,
> + struct resource *new_parent,
> + resource_size_t split_addr)
I'd call this "reparent_child_resources". But actually the function is
weird. Because you only reparents some resources from old to now.
Two questions:
a) Is split_addr really required. Couldn't we derive that from "old_parent"
b) Could we somehow make it clearer (variable names etc) that we are
only reparenting from "left" to "right" (maybe we can find better names).
Something like
/*
* Reparent all child resources that no longer belong to "low" after
* a split to "high". Note that "high" does not have any children,
* because "low" is the adjusted original resource and "high" is a new
* resource.
*/
static void reparent_children_after_split(struct resource *low,
struct resource *high)
Again, maybe we can find better names for left/right low/high.
[...]
> *
> * Note:
> * - Additional release conditions, such as overlapping region, can be
> * supported after they are confirmed as valid cases.
> - * - When a busy memory resource gets split into two entries, the code
> - * assumes that all children remain in the lower address entry for
> - * simplicity. Enhance this logic when necessary.
> + * - When a busy memory resource gets split into two entries, its children is
s/is/are/
> + * reassigned to the correct parent based on their range. If a child memory
> + * resource overlaps with more than one parent, enhance the logic as needed.
> */
> void release_mem_region_adjustable(resource_size_t start, resource_size_t size)
> {
> @@ -1482,6 +1515,7 @@ void release_mem_region_adjustable(resource_size_t start, resource_size_t size)
> new_res->parent = res->parent;
> new_res->sibling = res->sibling;
> new_res->child = NULL;
> + move_children_to_parent(res, new_res, end);
>
> if (WARN_ON_ONCE(__adjust_resource(res, res->start,
> start - res->start)))
--
Cheers
David / dhildenb
Powered by blists - more mailing lists