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Message-ID: <20250911140004.2241566-1-sumanthk@linux.ibm.com>
Date: Thu, 11 Sep 2025 16:00:04 +0200
From: Sumanth Korikkar <sumanthk@...ux.ibm.com>
To: Andrew Morton <akpm@...ux-foundation.org>, linux-mm <linux-mm@...ck.org>
Cc: linux-s390@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
David Hildenbrand <david@...hat.com>,
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>, sumanthk@...ux.ibm.com
Subject: [PATCH] resource: Improve child resource handling in release_mem_region_adjustable()
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
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].
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.
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
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;
+ } 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)
+{
+ struct resource *child, *next, **p;
+
+ p = &old_parent->child;
+ while ((child = *p)) {
+ next = child->sibling;
+ if (child->start > split_addr) {
+ /* unlink child */
+ *p = next;
+ append_child_to_parent(new_parent, child);
+ } else {
+ p = &child->sibling;
+ }
+ }
+}
+
/**
* release_mem_region_adjustable - release a previously reserved memory region
* @start: resource start address
@@ -1397,15 +1432,13 @@ EXPORT_SYMBOL(__release_region);
* is released from a currently busy memory resource. The requested region
* must either match exactly or fit into a single busy resource entry. In
* the latter case, the remaining resource is adjusted accordingly.
- * Existing children of the busy memory resource must be immutable in the
- * request.
*
* 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
+ * 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)))
--
2.48.1
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