[V7,1/3] mm/hotplug: Reorder memblock_[free|remove]() calls in try_remove_memory()
diff mbox series

Message ID 1567503958-25831-2-git-send-email-anshuman.khandual@arm.com
State New
Headers show
Series
  • arm64/mm: Enable memory hot remove
Related show

Commit Message

Anshuman Khandual Sept. 3, 2019, 9:45 a.m. UTC
Memory hot remove uses get_nid_for_pfn() while tearing down linked sysfs
entries between memory block and node. It first checks pfn validity with
pfn_valid_within() before fetching nid. With CONFIG_HOLES_IN_ZONE config
(arm64 has this enabled) pfn_valid_within() calls pfn_valid().

pfn_valid() is an arch implementation on arm64 (CONFIG_HAVE_ARCH_PFN_VALID)
which scans all mapped memblock regions with memblock_is_map_memory(). This
creates a problem in memory hot remove path which has already removed given
memory range from memory block with memblock_[remove|free] before arriving
at unregister_mem_sect_under_nodes(). Hence get_nid_for_pfn() returns -1
skipping subsequent sysfs_remove_link() calls leaving node <-> memory block
sysfs entries as is. Subsequent memory add operation hits BUG_ON() because
of existing sysfs entries.

[   62.007176] NUMA: Unknown node for memory at 0x680000000, assuming node 0
[   62.052517] ------------[ cut here ]------------
[   62.053211] kernel BUG at mm/memory_hotplug.c:1143!
[   62.053868] Internal error: Oops - BUG: 0 [#1] PREEMPT SMP
[   62.054589] Modules linked in:
[   62.054999] CPU: 19 PID: 3275 Comm: bash Not tainted 5.1.0-rc2-00004-g28cea40b2683 #41
[   62.056274] Hardware name: linux,dummy-virt (DT)
[   62.057166] pstate: 40400005 (nZcv daif +PAN -UAO)
[   62.058083] pc : add_memory_resource+0x1cc/0x1d8
[   62.058961] lr : add_memory_resource+0x10c/0x1d8
[   62.059842] sp : ffff0000168b3ce0
[   62.060477] x29: ffff0000168b3ce0 x28: ffff8005db546c00
[   62.061501] x27: 0000000000000000 x26: 0000000000000000
[   62.062509] x25: ffff0000111ef000 x24: ffff0000111ef5d0
[   62.063520] x23: 0000000000000000 x22: 00000006bfffffff
[   62.064540] x21: 00000000ffffffef x20: 00000000006c0000
[   62.065558] x19: 0000000000680000 x18: 0000000000000024
[   62.066566] x17: 0000000000000000 x16: 0000000000000000
[   62.067579] x15: ffffffffffffffff x14: ffff8005e412e890
[   62.068588] x13: ffff8005d6b105d8 x12: 0000000000000000
[   62.069610] x11: ffff8005d6b10490 x10: 0000000000000040
[   62.070615] x9 : ffff8005e412e898 x8 : ffff8005e412e890
[   62.071631] x7 : ffff8005d6b105d8 x6 : ffff8005db546c00
[   62.072640] x5 : 0000000000000001 x4 : 0000000000000002
[   62.073654] x3 : ffff8005d7049480 x2 : 0000000000000002
[   62.074666] x1 : 0000000000000003 x0 : 00000000ffffffef
[   62.075685] Process bash (pid: 3275, stack limit = 0x00000000d754280f)
[   62.076930] Call trace:
[   62.077411]  add_memory_resource+0x1cc/0x1d8
[   62.078227]  __add_memory+0x70/0xa8
[   62.078901]  probe_store+0xa4/0xc8
[   62.079561]  dev_attr_store+0x18/0x28
[   62.080270]  sysfs_kf_write+0x40/0x58
[   62.080992]  kernfs_fop_write+0xcc/0x1d8
[   62.081744]  __vfs_write+0x18/0x40
[   62.082400]  vfs_write+0xa4/0x1b0
[   62.083037]  ksys_write+0x5c/0xc0
[   62.083681]  __arm64_sys_write+0x18/0x20
[   62.084432]  el0_svc_handler+0x88/0x100
[   62.085177]  el0_svc+0x8/0xc

Re-ordering memblock_[free|remove]() with arch_remove_memory() solves the
problem on arm64 as pfn_valid() behaves correctly and returns positive
as memblock for the address range still exists. arch_remove_memory()
removes applicable memory sections from zone with __remove_pages() and
tears down kernel linear mapping. Removing memblock regions afterwards
is safe because there is no other memblock (bootmem) allocator user that
late. So nobody is going to allocate from the removed range just to blow
up later. Also nobody should be using the bootmem allocated range else
we wouldn't allow to remove it. So reordering is indeed safe.

Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
---
 mm/memory_hotplug.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

Comments

David Hildenbrand Sept. 4, 2019, 8:16 a.m. UTC | #1
On 03.09.19 11:45, Anshuman Khandual wrote:
> Memory hot remove uses get_nid_for_pfn() while tearing down linked sysfs
> entries between memory block and node. It first checks pfn validity with
> pfn_valid_within() before fetching nid. With CONFIG_HOLES_IN_ZONE config
> (arm64 has this enabled) pfn_valid_within() calls pfn_valid().
> 
> pfn_valid() is an arch implementation on arm64 (CONFIG_HAVE_ARCH_PFN_VALID)
> which scans all mapped memblock regions with memblock_is_map_memory(). This
> creates a problem in memory hot remove path which has already removed given
> memory range from memory block with memblock_[remove|free] before arriving
> at unregister_mem_sect_under_nodes(). Hence get_nid_for_pfn() returns -1
> skipping subsequent sysfs_remove_link() calls leaving node <-> memory block
> sysfs entries as is. Subsequent memory add operation hits BUG_ON() because
> of existing sysfs entries.

Since

commit 60bb462fc7adb06ebee3beb5a4af6c7e6182e248
Author: David Hildenbrand <david@redhat.com>
Date:   Wed Aug 28 13:57:15 2019 +1000

    drivers/base/node.c: simplify unregister_memory_block_under_nodes()

that problem should be gone. There is no get_nid_for_pfn() call anymore.

So this patch should no longer be necessary - but as I said during
earlier versions of this patch, the re-ordering might still make sense
for consistency (removing stuff in the reverse order they were added).
You'll have to rephrase the description then.

> 
> [   62.007176] NUMA: Unknown node for memory at 0x680000000, assuming node 0
> [   62.052517] ------------[ cut here ]------------
> [   62.053211] kernel BUG at mm/memory_hotplug.c:1143!
> [   62.053868] Internal error: Oops - BUG: 0 [#1] PREEMPT SMP
> [   62.054589] Modules linked in:
> [   62.054999] CPU: 19 PID: 3275 Comm: bash Not tainted 5.1.0-rc2-00004-g28cea40b2683 #41
> [   62.056274] Hardware name: linux,dummy-virt (DT)
> [   62.057166] pstate: 40400005 (nZcv daif +PAN -UAO)
> [   62.058083] pc : add_memory_resource+0x1cc/0x1d8
> [   62.058961] lr : add_memory_resource+0x10c/0x1d8
> [   62.059842] sp : ffff0000168b3ce0
> [   62.060477] x29: ffff0000168b3ce0 x28: ffff8005db546c00
> [   62.061501] x27: 0000000000000000 x26: 0000000000000000
> [   62.062509] x25: ffff0000111ef000 x24: ffff0000111ef5d0
> [   62.063520] x23: 0000000000000000 x22: 00000006bfffffff
> [   62.064540] x21: 00000000ffffffef x20: 00000000006c0000
> [   62.065558] x19: 0000000000680000 x18: 0000000000000024
> [   62.066566] x17: 0000000000000000 x16: 0000000000000000
> [   62.067579] x15: ffffffffffffffff x14: ffff8005e412e890
> [   62.068588] x13: ffff8005d6b105d8 x12: 0000000000000000
> [   62.069610] x11: ffff8005d6b10490 x10: 0000000000000040
> [   62.070615] x9 : ffff8005e412e898 x8 : ffff8005e412e890
> [   62.071631] x7 : ffff8005d6b105d8 x6 : ffff8005db546c00
> [   62.072640] x5 : 0000000000000001 x4 : 0000000000000002
> [   62.073654] x3 : ffff8005d7049480 x2 : 0000000000000002
> [   62.074666] x1 : 0000000000000003 x0 : 00000000ffffffef
> [   62.075685] Process bash (pid: 3275, stack limit = 0x00000000d754280f)
> [   62.076930] Call trace:
> [   62.077411]  add_memory_resource+0x1cc/0x1d8
> [   62.078227]  __add_memory+0x70/0xa8
> [   62.078901]  probe_store+0xa4/0xc8
> [   62.079561]  dev_attr_store+0x18/0x28
> [   62.080270]  sysfs_kf_write+0x40/0x58
> [   62.080992]  kernfs_fop_write+0xcc/0x1d8
> [   62.081744]  __vfs_write+0x18/0x40
> [   62.082400]  vfs_write+0xa4/0x1b0
> [   62.083037]  ksys_write+0x5c/0xc0
> [   62.083681]  __arm64_sys_write+0x18/0x20
> [   62.084432]  el0_svc_handler+0x88/0x100
> [   62.085177]  el0_svc+0x8/0xc
> 
> Re-ordering memblock_[free|remove]() with arch_remove_memory() solves the
> problem on arm64 as pfn_valid() behaves correctly and returns positive
> as memblock for the address range still exists. arch_remove_memory()
> removes applicable memory sections from zone with __remove_pages() and
> tears down kernel linear mapping. Removing memblock regions afterwards
> is safe because there is no other memblock (bootmem) allocator user that
> late. So nobody is going to allocate from the removed range just to blow
> up later. Also nobody should be using the bootmem allocated range else
> we wouldn't allow to remove it. So reordering is indeed safe.
> 
> Reviewed-by: David Hildenbrand <david@redhat.com>
> Reviewed-by: Oscar Salvador <osalvador@suse.de>
> Acked-by: Mark Rutland <mark.rutland@arm.com>
> Acked-by: Michal Hocko <mhocko@suse.com>
> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
> ---
>  mm/memory_hotplug.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index c73f09913165..355c466e0621 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1770,13 +1770,13 @@ static int __ref try_remove_memory(int nid, u64 start, u64 size)
>  
>  	/* remove memmap entry */
>  	firmware_map_remove(start, start + size, "System RAM");
> -	memblock_free(start, size);
> -	memblock_remove(start, size);
>  
>  	/* remove memory block devices before removing memory */
>  	remove_memory_block_devices(start, size);
>  
>  	arch_remove_memory(nid, start, size, NULL);
> +	memblock_free(start, size);
> +	memblock_remove(start, size);
>  	__release_memory_resource(start, size);
>  
>  	try_offline_node(nid);
>
Anshuman Khandual Sept. 5, 2019, 4:27 a.m. UTC | #2
On 09/04/2019 01:46 PM, David Hildenbrand wrote:
> On 03.09.19 11:45, Anshuman Khandual wrote:
>> Memory hot remove uses get_nid_for_pfn() while tearing down linked sysfs
>> entries between memory block and node. It first checks pfn validity with
>> pfn_valid_within() before fetching nid. With CONFIG_HOLES_IN_ZONE config
>> (arm64 has this enabled) pfn_valid_within() calls pfn_valid().
>>
>> pfn_valid() is an arch implementation on arm64 (CONFIG_HAVE_ARCH_PFN_VALID)
>> which scans all mapped memblock regions with memblock_is_map_memory(). This
>> creates a problem in memory hot remove path which has already removed given
>> memory range from memory block with memblock_[remove|free] before arriving
>> at unregister_mem_sect_under_nodes(). Hence get_nid_for_pfn() returns -1
>> skipping subsequent sysfs_remove_link() calls leaving node <-> memory block
>> sysfs entries as is. Subsequent memory add operation hits BUG_ON() because
>> of existing sysfs entries.
> Since
> 
> commit 60bb462fc7adb06ebee3beb5a4af6c7e6182e248
> Author: David Hildenbrand <david@redhat.com>
> Date:   Wed Aug 28 13:57:15 2019 +1000
> 
>     drivers/base/node.c: simplify unregister_memory_block_under_nodes()
> 
> that problem should be gone. There is no get_nid_for_pfn() call anymore.

Yes, the problem is gone. The above commit is still not present on arm64
tree against which this series was rebased and tested while posting.

> 
> So this patch should no longer be necessary - but as I said during
> earlier versions of this patch, the re-ordering might still make sense
> for consistency (removing stuff in the reverse order they were added).
> You'll have to rephrase the description then.

Sure will reword the commit message on these lines.
Balbir Singh Sept. 16, 2019, 1:44 a.m. UTC | #3
On 3/9/19 7:45 pm, Anshuman Khandual wrote:
> Memory hot remove uses get_nid_for_pfn() while tearing down linked sysfs

I could not find this path in the code, the only called for get_nid_for_pfn()
was register_mem_sect_under_node() when the system is under boot.

> entries between memory block and node. It first checks pfn validity with
> pfn_valid_within() before fetching nid. With CONFIG_HOLES_IN_ZONE config
> (arm64 has this enabled) pfn_valid_within() calls pfn_valid().
> 
> pfn_valid() is an arch implementation on arm64 (CONFIG_HAVE_ARCH_PFN_VALID)
> which scans all mapped memblock regions with memblock_is_map_memory(). This
> creates a problem in memory hot remove path which has already removed given
> memory range from memory block with memblock_[remove|free] before arriving
> at unregister_mem_sect_under_nodes(). Hence get_nid_for_pfn() returns -1
> skipping subsequent sysfs_remove_link() calls leaving node <-> memory block
> sysfs entries as is. Subsequent memory add operation hits BUG_ON() because
> of existing sysfs entries.
> 
> [   62.007176] NUMA: Unknown node for memory at 0x680000000, assuming node 0
> [   62.052517] ------------[ cut here ]------------

This seems like arm64 is not ready for probe_store() via drivers/base/memory.c/ode.c

> [   62.053211] kernel BUG at mm/memory_hotplug.c:1143!



> [   62.053868] Internal error: Oops - BUG: 0 [#1] PREEMPT SMP
> [   62.054589] Modules linked in:
> [   62.054999] CPU: 19 PID: 3275 Comm: bash Not tainted 5.1.0-rc2-00004-g28cea40b2683 #41
> [   62.056274] Hardware name: linux,dummy-virt (DT)
> [   62.057166] pstate: 40400005 (nZcv daif +PAN -UAO)
> [   62.058083] pc : add_memory_resource+0x1cc/0x1d8
> [   62.058961] lr : add_memory_resource+0x10c/0x1d8
> [   62.059842] sp : ffff0000168b3ce0
> [   62.060477] x29: ffff0000168b3ce0 x28: ffff8005db546c00
> [   62.061501] x27: 0000000000000000 x26: 0000000000000000
> [   62.062509] x25: ffff0000111ef000 x24: ffff0000111ef5d0
> [   62.063520] x23: 0000000000000000 x22: 00000006bfffffff
> [   62.064540] x21: 00000000ffffffef x20: 00000000006c0000
> [   62.065558] x19: 0000000000680000 x18: 0000000000000024
> [   62.066566] x17: 0000000000000000 x16: 0000000000000000
> [   62.067579] x15: ffffffffffffffff x14: ffff8005e412e890
> [   62.068588] x13: ffff8005d6b105d8 x12: 0000000000000000
> [   62.069610] x11: ffff8005d6b10490 x10: 0000000000000040
> [   62.070615] x9 : ffff8005e412e898 x8 : ffff8005e412e890
> [   62.071631] x7 : ffff8005d6b105d8 x6 : ffff8005db546c00
> [   62.072640] x5 : 0000000000000001 x4 : 0000000000000002
> [   62.073654] x3 : ffff8005d7049480 x2 : 0000000000000002
> [   62.074666] x1 : 0000000000000003 x0 : 00000000ffffffef
> [   62.075685] Process bash (pid: 3275, stack limit = 0x00000000d754280f)
> [   62.076930] Call trace:
> [   62.077411]  add_memory_resource+0x1cc/0x1d8
> [   62.078227]  __add_memory+0x70/0xa8
> [   62.078901]  probe_store+0xa4/0xc8
> [   62.079561]  dev_attr_store+0x18/0x28
> [   62.080270]  sysfs_kf_write+0x40/0x58
> [   62.080992]  kernfs_fop_write+0xcc/0x1d8
> [   62.081744]  __vfs_write+0x18/0x40
> [   62.082400]  vfs_write+0xa4/0x1b0
> [   62.083037]  ksys_write+0x5c/0xc0
> [   62.083681]  __arm64_sys_write+0x18/0x20
> [   62.084432]  el0_svc_handler+0x88/0x100
> [   62.085177]  el0_svc+0x8/0xc
> 
> Re-ordering memblock_[free|remove]() with arch_remove_memory() solves the
> problem on arm64 as pfn_valid() behaves correctly and returns positive
> as memblock for the address range still exists. arch_remove_memory()
> removes applicable memory sections from zone with __remove_pages() and
> tears down kernel linear mapping. Removing memblock regions afterwards
> is safe because there is no other memblock (bootmem) allocator user that
> late. So nobody is going to allocate from the removed range just to blow
> up later. Also nobody should be using the bootmem allocated range else
> we wouldn't allow to remove it. So reordering is indeed safe.
> 
> Reviewed-by: David Hildenbrand <david@redhat.com>
> Reviewed-by: Oscar Salvador <osalvador@suse.de>
> Acked-by: Mark Rutland <mark.rutland@arm.com>
> Acked-by: Michal Hocko <mhocko@suse.com>
> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
> ---

Honestly, the issue is not clear from the changelog, largely
because I can't find the use of get_nid_for_pfn()  being used
in memory hotunplug. I can see why using pfn_valid() after
memblock_free/remove is bad on the architecture.

I think the checks to pfn_valid() can be avoided from the
remove paths if we did the following

memblock_isolate_regions()
for each isolate_region {
	memblock_free
	memblock_remove
	arch_memory_remove

	# ensure that __remove_memory can avoid calling pfn_valid
}

Having said that, your patch is easier and if your assumption
about not using the memblocks is valid (after arch_memory_remove())
then might be the least resistant way forward

Balbir Singh.


>  mm/memory_hotplug.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index c73f09913165..355c466e0621 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1770,13 +1770,13 @@ static int __ref try_remove_memory(int nid, u64 start, u64 size)
>  
>  	/* remove memmap entry */
>  	firmware_map_remove(start, start + size, "System RAM");
> -	memblock_free(start, size);
> -	memblock_remove(start, size);
>  
>  	/* remove memory block devices before removing memory */
>  	remove_memory_block_devices(start, size);
>  
>  	arch_remove_memory(nid, start, size, NULL);
> +	memblock_free(start, size);
> +	memblock_remove(start, size);
>  	__release_memory_resource(start, size);
>  
>  	try_offline_node(nid);
>
Anshuman Khandual Sept. 18, 2019, 9:28 a.m. UTC | #4
On 09/16/2019 07:14 AM, Balbir Singh wrote:
> 
> 
> On 3/9/19 7:45 pm, Anshuman Khandual wrote:
>> Memory hot remove uses get_nid_for_pfn() while tearing down linked sysfs
> 
> I could not find this path in the code, the only called for get_nid_for_pfn()
> was register_mem_sect_under_node() when the system is under boot.
> 
>> entries between memory block and node. It first checks pfn validity with
>> pfn_valid_within() before fetching nid. With CONFIG_HOLES_IN_ZONE config
>> (arm64 has this enabled) pfn_valid_within() calls pfn_valid().
>>
>> pfn_valid() is an arch implementation on arm64 (CONFIG_HAVE_ARCH_PFN_VALID)
>> which scans all mapped memblock regions with memblock_is_map_memory(). This
>> creates a problem in memory hot remove path which has already removed given
>> memory range from memory block with memblock_[remove|free] before arriving
>> at unregister_mem_sect_under_nodes(). Hence get_nid_for_pfn() returns -1
>> skipping subsequent sysfs_remove_link() calls leaving node <-> memory block
>> sysfs entries as is. Subsequent memory add operation hits BUG_ON() because
>> of existing sysfs entries.
>>
>> [   62.007176] NUMA: Unknown node for memory at 0x680000000, assuming node 0
>> [   62.052517] ------------[ cut here ]------------
> 
> This seems like arm64 is not ready for probe_store() via drivers/base/memory.c/ode.c
> 
>> [   62.053211] kernel BUG at mm/memory_hotplug.c:1143!
> 
> 
> 
>> [   62.053868] Internal error: Oops - BUG: 0 [#1] PREEMPT SMP
>> [   62.054589] Modules linked in:
>> [   62.054999] CPU: 19 PID: 3275 Comm: bash Not tainted 5.1.0-rc2-00004-g28cea40b2683 #41
>> [   62.056274] Hardware name: linux,dummy-virt (DT)
>> [   62.057166] pstate: 40400005 (nZcv daif +PAN -UAO)
>> [   62.058083] pc : add_memory_resource+0x1cc/0x1d8
>> [   62.058961] lr : add_memory_resource+0x10c/0x1d8
>> [   62.059842] sp : ffff0000168b3ce0
>> [   62.060477] x29: ffff0000168b3ce0 x28: ffff8005db546c00
>> [   62.061501] x27: 0000000000000000 x26: 0000000000000000
>> [   62.062509] x25: ffff0000111ef000 x24: ffff0000111ef5d0
>> [   62.063520] x23: 0000000000000000 x22: 00000006bfffffff
>> [   62.064540] x21: 00000000ffffffef x20: 00000000006c0000
>> [   62.065558] x19: 0000000000680000 x18: 0000000000000024
>> [   62.066566] x17: 0000000000000000 x16: 0000000000000000
>> [   62.067579] x15: ffffffffffffffff x14: ffff8005e412e890
>> [   62.068588] x13: ffff8005d6b105d8 x12: 0000000000000000
>> [   62.069610] x11: ffff8005d6b10490 x10: 0000000000000040
>> [   62.070615] x9 : ffff8005e412e898 x8 : ffff8005e412e890
>> [   62.071631] x7 : ffff8005d6b105d8 x6 : ffff8005db546c00
>> [   62.072640] x5 : 0000000000000001 x4 : 0000000000000002
>> [   62.073654] x3 : ffff8005d7049480 x2 : 0000000000000002
>> [   62.074666] x1 : 0000000000000003 x0 : 00000000ffffffef
>> [   62.075685] Process bash (pid: 3275, stack limit = 0x00000000d754280f)
>> [   62.076930] Call trace:
>> [   62.077411]  add_memory_resource+0x1cc/0x1d8
>> [   62.078227]  __add_memory+0x70/0xa8
>> [   62.078901]  probe_store+0xa4/0xc8
>> [   62.079561]  dev_attr_store+0x18/0x28
>> [   62.080270]  sysfs_kf_write+0x40/0x58
>> [   62.080992]  kernfs_fop_write+0xcc/0x1d8
>> [   62.081744]  __vfs_write+0x18/0x40
>> [   62.082400]  vfs_write+0xa4/0x1b0
>> [   62.083037]  ksys_write+0x5c/0xc0
>> [   62.083681]  __arm64_sys_write+0x18/0x20
>> [   62.084432]  el0_svc_handler+0x88/0x100
>> [   62.085177]  el0_svc+0x8/0xc
>>
>> Re-ordering memblock_[free|remove]() with arch_remove_memory() solves the
>> problem on arm64 as pfn_valid() behaves correctly and returns positive
>> as memblock for the address range still exists. arch_remove_memory()
>> removes applicable memory sections from zone with __remove_pages() and
>> tears down kernel linear mapping. Removing memblock regions afterwards
>> is safe because there is no other memblock (bootmem) allocator user that
>> late. So nobody is going to allocate from the removed range just to blow
>> up later. Also nobody should be using the bootmem allocated range else
>> we wouldn't allow to remove it. So reordering is indeed safe.
>>
>> Reviewed-by: David Hildenbrand <david@redhat.com>
>> Reviewed-by: Oscar Salvador <osalvador@suse.de>
>> Acked-by: Mark Rutland <mark.rutland@arm.com>
>> Acked-by: Michal Hocko <mhocko@suse.com>
>> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
>> ---
> 
> Honestly, the issue is not clear from the changelog, largely
> because I can't find the use of get_nid_for_pfn()  being used
> in memory hotunplug. I can see why using pfn_valid() after
> memblock_free/remove is bad on the architecture.
> 
> I think the checks to pfn_valid() can be avoided from the
> remove paths if we did the following
> 
> memblock_isolate_regions()
> for each isolate_region {
> 	memblock_free
> 	memblock_remove
> 	arch_memory_remove
> 
> 	# ensure that __remove_memory can avoid calling pfn_valid
> }
> 
> Having said that, your patch is easier and if your assumption
> about not using the memblocks is valid (after arch_memory_remove())
> then might be the least resistant way forward

The context for this patch has changed a bit which now reflects in
it's current posting (https://patchwork.kernel.org/patch/11146361/)

Patch
diff mbox series

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index c73f09913165..355c466e0621 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1770,13 +1770,13 @@  static int __ref try_remove_memory(int nid, u64 start, u64 size)
 
 	/* remove memmap entry */
 	firmware_map_remove(start, start + size, "System RAM");
-	memblock_free(start, size);
-	memblock_remove(start, size);
 
 	/* remove memory block devices before removing memory */
 	remove_memory_block_devices(start, size);
 
 	arch_remove_memory(nid, start, size, NULL);
+	memblock_free(start, size);
+	memblock_remove(start, size);
 	__release_memory_resource(start, size);
 
 	try_offline_node(nid);