s390: drop memory notifier for protecting kdump crash kernel area
Subsystems (2)
PATCH 1/1 s390: drop memory notifier for protecting kdump crash kernel area
Assume we have a crashkernel area of 256MB reserved:
root@vm0:~# cat /proc/iomem 00000000-6fffffff : System RAM 0f258000-0fcfffff : Kernel code 0fd00000-101d10e3 : Kernel data 105b3000-1068dfff : Kernel bss 70000000-7fffffff : Crash kernel
This exactly corresponds to memory block 7 (memory block size is 256MB). Trying to offline that memory block results in:
root@vm0:~# echo "offline" > /sys/devices/system/memory/memory7/state -bash: echo: write error: Device or resource busy
[ 128.458762] page:000003d081c00000 refcount:1 mapcount:0 mapping:00000000d01cecd4 index:0x0 [ 128.458773] flags: 0x1ffff00000001000(reserved) [ 128.458781] raw: 1ffff00000001000 000003d081c00008 000003d081c00008 0000000000000000 [ 128.458781] raw: 0000000000000000 0000000000000000 ffffffff00000001 0000000000000000 [ 128.458783] page dumped because: unmovable page
The craskernel area is marked reserved in the bootmem allocator. This results in the memmap getting initialized (refcount=1, PG_reserved), but the pages are never freed to the page allocator.
So these pages look like allocated pages that are unmovable (esp. PG_reserved), and therefore, memory offlining fails early, when trying to isolate the page range.
We don't need a special memory notifier and can drop it. Repeating the above test with this patch results in the same behavior.
--- arch/s390/kernel/setup.c | 33 --------------------------------- 1 file changed, 33 deletions(-)
arch/s390/kernel/setup.c +0 -33
@@ -39,7 +39,6 @@#include <linux/kernel_stat.h> #include <linux/dma-contiguous.h> #include <linux/device.h> -#include <linux/notifier.h> #include <linux/pfn.h> #include <linux/ctype.h> #include <linux/reboot.h>
@@ -591,35 +590,6 @@ static void __init setup_memory_end(void)pr_notice ("The maximum memory size is %luMB\n" , memory_end >>20 ); } -#ifdef CONFIG_CRASH_DUMP - -/* -* When kdump is enabled, we have to ensure that no memory from -* the area [0 - crashkernel memory size] and -* [crashk_res.start - crashk_res.end] is set offline. -*/ -static int kdump_mem_notifier (struct notifier_block *nb, -unsigned long action,void *data) -{ -struct memory_notify *arg = data; - -if (action !=MEM_GOING_OFFLINE ) -return NOTIFY_OK ; -if (arg->start_pfn <PFN_DOWN (resource_size (&crashk_res))) -return NOTIFY_BAD ; -if (arg->start_pfn >PFN_DOWN (crashk_res.end)) -return NOTIFY_OK ; -if (arg->start_pfn + arg->nr_pages -1 <PFN_DOWN (crashk_res.start)) -return NOTIFY_OK ; -return NOTIFY_BAD ; -} - -static struct notifier_block kdump_mem_nb = { - .notifier_call = kdump_mem_notifier, -}; - -#endif -/* * Make sure that the area behind memory_end is protected */
@@ -703,9 +673,6 @@ static void __init reserve_crashkernel(void)return ; } -if (register_memory_notifier (&kdump_mem_nb)) -return ; -if (!OLDMEM_BASE &&MACHINE_IS_VM )diag10_range (PFN_DOWN (crash_base),PFN_DOWN (crash_size)); crashk_res.start = crash_base;
Signature · 1 line
2.25.3
Quoted 58 lines · David Hildenbrand
Assume we have a crashkernel area of 256MB reserved:
root@vm0:~# cat /proc/iomem 00000000-6fffffff : System RAM 0f258000-0fcfffff : Kernel code 0fd00000-101d10e3 : Kernel data 105b3000-1068dfff : Kernel bss 70000000-7fffffff : Crash kernelThis exactly corresponds to memory block 7 (memory block size is 256MB). Trying to offline that memory block results in:
root@vm0:~# echo "offline" > /sys/devices/system/memory/memory7/state -bash: echo: write error: Device or resource busy[ 128.458762] page:000003d081c00000 refcount:1 mapcount:0 mapping:00000000d01cecd4 index:0x0 [ 128.458773] flags: 0x1ffff00000001000(reserved) [ 128.458781] raw: 1ffff00000001000 000003d081c00008 000003d081c00008 0000000000000000 [ 128.458781] raw: 0000000000000000 0000000000000000 ffffffff00000001 0000000000000000 [ 128.458783] page dumped because: unmovable pageThe craskernel area is marked reserved in the bootmem allocator. This results in the memmap getting initialized (refcount=1,
PG_reserved), but the pages are never freed to the page allocator.So these pages look like allocated pages that are unmovable (esp.
PG_reserved), and therefore, memory offlining fails early, when trying to isolate the page range.We don't need a special memory notifier and can drop it. Repeating the above test with this patch results in the same behavior.
Cc Heiko Carstens <[email protected]>Cc Vasily Gorbik <[email protected]>Cc Christian Borntraeger <[email protected]>Cc Martin Schwidefsky <[email protected]>Cc Philipp Rudo <[email protected]>Cc Gerald Schaefer <[email protected]>Cc Eric W. Biederman <[email protected]>Cc Michal Hocko <[email protected]>Signed-off-by David Hildenbrand <[email protected]>--- arch/s390/kernel/setup.c | 33 --------------------------------- 1 file changed, 33 deletions(-)arch/s390/kernel/setup.c +0
-1@@ -39,7 +39,6 @@#include <linux/kernel_stat.h> #include <linux/dma-contiguous.h> #include <linux/device.h> -#include <linux/notifier.h> #include <linux/pfn.h> #include <linux/ctype.h> #include <linux/reboot.h>
arch/s390/kernel/setup.c static void __init setup_memory_end(void) · line 600
Quoted 10 lines
arch/s390/kernel/setup.c +0
-7@@ -591,35 +590,6 @@ static void __init setup_memory_end(void)pr_notice ("The maximum memory size is %luMB\n" , memory_end >>20 ); } -#ifdef CONFIG_CRASH_DUMP - -/* -* When kdump is enabled, we have to ensure that no memory from -* the area [0 - crashkernel memory size] and -* [crashk_res.start - crashk_res.end] is set offline. -*/
Re-reading that comment, I missed the [0 - crashkernel memory size] part (for relocation IIRC). So we might want to keep checking for [0 - crashkernel memory size] - will double check.
Signature · 3 lines
Thanks, David / dhildenb