diff mbox series

[v2,1/7] kernel/resource: make release_mem_region_adjustable() never fail

Message ID 20200908201012.44168-2-david@redhat.com (mailing list archive)
State Superseded, archived
Headers show
Series [v2,1/7] kernel/resource: make release_mem_region_adjustable() never fail | expand

Commit Message

David Hildenbrand Sept. 8, 2020, 8:10 p.m. UTC
Let's make sure splitting a resource on memory hotunplug will never fail.
This will become more relevant once we merge selected System RAM
resources - then, we'll trigger that case more often on memory hotunplug.

In general, this function is already unlikely to fail. When we remove
memory, we free up quite a lot of metadata (memmap, page tables, memory
block device, etc.). The only reason it could really fail would be when
injecting allocation errors.

All other error cases inside release_mem_region_adjustable() seem to be
sanity checks if the function would be abused in different context -
let's add WARN_ON_ONCE() in these cases so we can catch them.

Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Kees Cook <keescook@chromium.org>
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Wei Yang <richardw.yang@linux.intel.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
 include/linux/ioport.h |  4 ++--
 kernel/resource.c      | 49 ++++++++++++++++++++++++------------------
 mm/memory_hotplug.c    | 22 +------------------
 3 files changed, 31 insertions(+), 44 deletions(-)

Comments

Wei Yang Sept. 15, 2020, 2:07 a.m. UTC | #1
On Tue, Sep 08, 2020 at 10:10:06PM +0200, David Hildenbrand wrote:
>Let's make sure splitting a resource on memory hotunplug will never fail.
>This will become more relevant once we merge selected System RAM
>resources - then, we'll trigger that case more often on memory hotunplug.
>
>In general, this function is already unlikely to fail. When we remove
>memory, we free up quite a lot of metadata (memmap, page tables, memory
>block device, etc.). The only reason it could really fail would be when
>injecting allocation errors.
>
>All other error cases inside release_mem_region_adjustable() seem to be
>sanity checks if the function would be abused in different context -
>let's add WARN_ON_ONCE() in these cases so we can catch them.
>
>Cc: Andrew Morton <akpm@linux-foundation.org>
>Cc: Michal Hocko <mhocko@suse.com>
>Cc: Dan Williams <dan.j.williams@intel.com>
>Cc: Jason Gunthorpe <jgg@ziepe.ca>
>Cc: Kees Cook <keescook@chromium.org>
>Cc: Ard Biesheuvel <ardb@kernel.org>
>Cc: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
>Cc: Baoquan He <bhe@redhat.com>
>Cc: Wei Yang <richardw.yang@linux.intel.com>
>Signed-off-by: David Hildenbrand <david@redhat.com>
>---
> include/linux/ioport.h |  4 ++--
> kernel/resource.c      | 49 ++++++++++++++++++++++++------------------
> mm/memory_hotplug.c    | 22 +------------------
> 3 files changed, 31 insertions(+), 44 deletions(-)
>
>diff --git a/include/linux/ioport.h b/include/linux/ioport.h
>index 6c2b06fe8beb7..52a91f5fa1a36 100644
>--- a/include/linux/ioport.h
>+++ b/include/linux/ioport.h
>@@ -248,8 +248,8 @@ extern struct resource * __request_region(struct resource *,
> extern void __release_region(struct resource *, resource_size_t,
> 				resource_size_t);
> #ifdef CONFIG_MEMORY_HOTREMOVE
>-extern int release_mem_region_adjustable(struct resource *, resource_size_t,
>-				resource_size_t);
>+extern void release_mem_region_adjustable(struct resource *, resource_size_t,
>+					  resource_size_t);
> #endif
> 
> /* Wrappers for managed devices */
>diff --git a/kernel/resource.c b/kernel/resource.c
>index f1175ce93a1d5..36b3552210120 100644
>--- a/kernel/resource.c
>+++ b/kernel/resource.c
>@@ -1258,21 +1258,28 @@ EXPORT_SYMBOL(__release_region);
>  *   assumes that all children remain in the lower address entry for
>  *   simplicity.  Enhance this logic when necessary.
>  */
>-int release_mem_region_adjustable(struct resource *parent,
>-				  resource_size_t start, resource_size_t size)
>+void release_mem_region_adjustable(struct resource *parent,
>+				   resource_size_t start, resource_size_t size)
> {
>+	struct resource *new_res = NULL;
>+	bool alloc_nofail = false;
> 	struct resource **p;
> 	struct resource *res;
>-	struct resource *new_res;
> 	resource_size_t end;
>-	int ret = -EINVAL;
> 
> 	end = start + size - 1;
>-	if ((start < parent->start) || (end > parent->end))
>-		return ret;
>+	if (WARN_ON_ONCE((start < parent->start) || (end > parent->end)))
>+		return;
> 
>-	/* The alloc_resource() result gets checked later */
>-	new_res = alloc_resource(GFP_KERNEL);
>+	/*
>+	 * We free up quite a lot of memory on memory hotunplug (esp., memap),
>+	 * just before releasing the region. This is highly unlikely to
>+	 * fail - let's play save and make it never fail as the caller cannot
>+	 * perform any error handling (e.g., trying to re-add memory will fail
>+	 * similarly).
>+	 */
>+retry:
>+	new_res = alloc_resource(GFP_KERNEL | alloc_nofail ? __GFP_NOFAIL : 0);
> 

It looks like a bold change, while I don't find a reason to object it.

> 	p = &parent->child;
> 	write_lock(&resource_lock);
>@@ -1298,7 +1305,6 @@ int release_mem_region_adjustable(struct resource *parent,
> 		 * so if we are dealing with them, let us just back off here.
> 		 */
> 		if (!(res->flags & IORESOURCE_SYSRAM)) {
>-			ret = 0;
> 			break;
> 		}
> 
>@@ -1315,20 +1321,23 @@ int release_mem_region_adjustable(struct resource *parent,
> 			/* free the whole entry */
> 			*p = res->sibling;
> 			free_resource(res);
>-			ret = 0;
> 		} else if (res->start == start && res->end != end) {
> 			/* adjust the start */
>-			ret = __adjust_resource(res, end + 1,
>-						res->end - end);
>+			WARN_ON_ONCE(__adjust_resource(res, end + 1,
>+						       res->end - end));
> 		} else if (res->start != start && res->end == end) {
> 			/* adjust the end */
>-			ret = __adjust_resource(res, res->start,
>-						start - res->start);
>+			WARN_ON_ONCE(__adjust_resource(res, res->start,
>+						       start - res->start));
> 		} else {
>-			/* split into two entries */
>+			/* split into two entries - we need a new resource */
> 			if (!new_res) {
>-				ret = -ENOMEM;
>-				break;
>+				new_res = alloc_resource(GFP_ATOMIC);
>+				if (!new_res) {
>+					alloc_nofail = true;
>+					write_unlock(&resource_lock);
>+					goto retry;
>+				}
> 			}
> 			new_res->name = res->name;
> 			new_res->start = end + 1;
>@@ -1339,9 +1348,8 @@ int release_mem_region_adjustable(struct resource *parent,
> 			new_res->sibling = res->sibling;
> 			new_res->child = NULL;
> 
>-			ret = __adjust_resource(res, res->start,
>-						start - res->start);
>-			if (ret)
>+			if (WARN_ON_ONCE(__adjust_resource(res, res->start,
>+							   start - res->start)))
> 				break;
> 			res->sibling = new_res;
> 			new_res = NULL;
>@@ -1352,7 +1360,6 @@ int release_mem_region_adjustable(struct resource *parent,
> 
> 	write_unlock(&resource_lock);
> 	free_resource(new_res);
>-	return ret;
> }
> #endif	/* CONFIG_MEMORY_HOTREMOVE */
> 
>diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
>index baded53b9ff92..4c47b68a9f4b5 100644
>--- a/mm/memory_hotplug.c
>+++ b/mm/memory_hotplug.c
>@@ -1724,26 +1724,6 @@ void try_offline_node(int nid)
> }
> EXPORT_SYMBOL(try_offline_node);
> 
>-static void __release_memory_resource(resource_size_t start,
>-				      resource_size_t size)
>-{
>-	int ret;
>-
>-	/*
>-	 * When removing memory in the same granularity as it was added,
>-	 * this function never fails. It might only fail if resources
>-	 * have to be adjusted or split. We'll ignore the error, as
>-	 * removing of memory cannot fail.
>-	 */
>-	ret = release_mem_region_adjustable(&iomem_resource, start, size);
>-	if (ret) {
>-		resource_size_t endres = start + size - 1;
>-
>-		pr_warn("Unable to release resource <%pa-%pa> (%d)\n",
>-			&start, &endres, ret);
>-	}
>-}
>-
> static int __ref try_remove_memory(int nid, u64 start, u64 size)
> {
> 	int rc = 0;
>@@ -1777,7 +1757,7 @@ static int __ref try_remove_memory(int nid, u64 start, u64 size)
> 		memblock_remove(start, size);
> 	}
> 
>-	__release_memory_resource(start, size);
>+	release_mem_region_adjustable(&iomem_resource, start, size);
> 
> 	try_offline_node(nid);
> 
>-- 
>2.26.2
Wei Yang Sept. 15, 2020, 2:10 a.m. UTC | #2
On Tue, Sep 08, 2020 at 10:10:06PM +0200, David Hildenbrand wrote:
>Let's make sure splitting a resource on memory hotunplug will never fail.
>This will become more relevant once we merge selected System RAM
>resources - then, we'll trigger that case more often on memory hotunplug.
>
>In general, this function is already unlikely to fail. When we remove
>memory, we free up quite a lot of metadata (memmap, page tables, memory
>block device, etc.). The only reason it could really fail would be when
>injecting allocation errors.
>
>All other error cases inside release_mem_region_adjustable() seem to be
>sanity checks if the function would be abused in different context -
>let's add WARN_ON_ONCE() in these cases so we can catch them.
>
>Cc: Andrew Morton <akpm@linux-foundation.org>
>Cc: Michal Hocko <mhocko@suse.com>
>Cc: Dan Williams <dan.j.williams@intel.com>
>Cc: Jason Gunthorpe <jgg@ziepe.ca>
>Cc: Kees Cook <keescook@chromium.org>
>Cc: Ard Biesheuvel <ardb@kernel.org>
>Cc: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
>Cc: Baoquan He <bhe@redhat.com>
>Cc: Wei Yang <richardw.yang@linux.intel.com>
>Signed-off-by: David Hildenbrand <david@redhat.com>
>---
> include/linux/ioport.h |  4 ++--
> kernel/resource.c      | 49 ++++++++++++++++++++++++------------------
> mm/memory_hotplug.c    | 22 +------------------
> 3 files changed, 31 insertions(+), 44 deletions(-)
>
>diff --git a/include/linux/ioport.h b/include/linux/ioport.h
>index 6c2b06fe8beb7..52a91f5fa1a36 100644
>--- a/include/linux/ioport.h
>+++ b/include/linux/ioport.h
>@@ -248,8 +248,8 @@ extern struct resource * __request_region(struct resource *,
> extern void __release_region(struct resource *, resource_size_t,
> 				resource_size_t);
> #ifdef CONFIG_MEMORY_HOTREMOVE
>-extern int release_mem_region_adjustable(struct resource *, resource_size_t,
>-				resource_size_t);
>+extern void release_mem_region_adjustable(struct resource *, resource_size_t,
>+					  resource_size_t);
> #endif
> 
> /* Wrappers for managed devices */
>diff --git a/kernel/resource.c b/kernel/resource.c
>index f1175ce93a1d5..36b3552210120 100644
>--- a/kernel/resource.c
>+++ b/kernel/resource.c
>@@ -1258,21 +1258,28 @@ EXPORT_SYMBOL(__release_region);
>  *   assumes that all children remain in the lower address entry for
>  *   simplicity.  Enhance this logic when necessary.
>  */
>-int release_mem_region_adjustable(struct resource *parent,
>-				  resource_size_t start, resource_size_t size)
>+void release_mem_region_adjustable(struct resource *parent,
>+				   resource_size_t start, resource_size_t size)
> {
>+	struct resource *new_res = NULL;
>+	bool alloc_nofail = false;
> 	struct resource **p;
> 	struct resource *res;
>-	struct resource *new_res;
> 	resource_size_t end;
>-	int ret = -EINVAL;
> 
> 	end = start + size - 1;
>-	if ((start < parent->start) || (end > parent->end))
>-		return ret;
>+	if (WARN_ON_ONCE((start < parent->start) || (end > parent->end)))
>+		return;
> 
>-	/* The alloc_resource() result gets checked later */
>-	new_res = alloc_resource(GFP_KERNEL);
>+	/*
>+	 * We free up quite a lot of memory on memory hotunplug (esp., memap),
>+	 * just before releasing the region. This is highly unlikely to
>+	 * fail - let's play save and make it never fail as the caller cannot
>+	 * perform any error handling (e.g., trying to re-add memory will fail
>+	 * similarly).
>+	 */
>+retry:
>+	new_res = alloc_resource(GFP_KERNEL | alloc_nofail ? __GFP_NOFAIL : 0);
> 
> 	p = &parent->child;
> 	write_lock(&resource_lock);
>@@ -1298,7 +1305,6 @@ int release_mem_region_adjustable(struct resource *parent,
> 		 * so if we are dealing with them, let us just back off here.
> 		 */
> 		if (!(res->flags & IORESOURCE_SYSRAM)) {
>-			ret = 0;
> 			break;
> 		}
> 
>@@ -1315,20 +1321,23 @@ int release_mem_region_adjustable(struct resource *parent,
> 			/* free the whole entry */
> 			*p = res->sibling;
> 			free_resource(res);
>-			ret = 0;
> 		} else if (res->start == start && res->end != end) {
> 			/* adjust the start */
>-			ret = __adjust_resource(res, end + 1,
>-						res->end - end);
>+			WARN_ON_ONCE(__adjust_resource(res, end + 1,
>+						       res->end - end));
> 		} else if (res->start != start && res->end == end) {
> 			/* adjust the end */
>-			ret = __adjust_resource(res, res->start,
>-						start - res->start);
>+			WARN_ON_ONCE(__adjust_resource(res, res->start,
>+						       start - res->start));
> 		} else {
>-			/* split into two entries */
>+			/* split into two entries - we need a new resource */
> 			if (!new_res) {
>-				ret = -ENOMEM;
>-				break;
>+				new_res = alloc_resource(GFP_ATOMIC);
>+				if (!new_res) {
>+					alloc_nofail = true;
>+					write_unlock(&resource_lock);
>+					goto retry;
>+				}
> 			}
> 			new_res->name = res->name;
> 			new_res->start = end + 1;
>@@ -1339,9 +1348,8 @@ int release_mem_region_adjustable(struct resource *parent,
> 			new_res->sibling = res->sibling;
> 			new_res->child = NULL;
> 
>-			ret = __adjust_resource(res, res->start,
>-						start - res->start);
>-			if (ret)
>+			if (WARN_ON_ONCE(__adjust_resource(res, res->start,
>+							   start - res->start)))
> 				break;
> 			res->sibling = new_res;
> 			new_res = NULL;
>@@ -1352,7 +1360,6 @@ int release_mem_region_adjustable(struct resource *parent,
> 
> 	write_unlock(&resource_lock);
> 	free_resource(new_res);
>-	return ret;
> }
> #endif	/* CONFIG_MEMORY_HOTREMOVE */
> 
>diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
>index baded53b9ff92..4c47b68a9f4b5 100644
>--- a/mm/memory_hotplug.c
>+++ b/mm/memory_hotplug.c
>@@ -1724,26 +1724,6 @@ void try_offline_node(int nid)
> }
> EXPORT_SYMBOL(try_offline_node);
> 
>-static void __release_memory_resource(resource_size_t start,
>-				      resource_size_t size)
>-{
>-	int ret;
>-
>-	/*
>-	 * When removing memory in the same granularity as it was added,
>-	 * this function never fails. It might only fail if resources
>-	 * have to be adjusted or split. We'll ignore the error, as
>-	 * removing of memory cannot fail.
>-	 */
>-	ret = release_mem_region_adjustable(&iomem_resource, start, size);
>-	if (ret) {
>-		resource_size_t endres = start + size - 1;
>-
>-		pr_warn("Unable to release resource <%pa-%pa> (%d)\n",
>-			&start, &endres, ret);
>-	}
>-}
>-
> static int __ref try_remove_memory(int nid, u64 start, u64 size)
> {
> 	int rc = 0;
>@@ -1777,7 +1757,7 @@ static int __ref try_remove_memory(int nid, u64 start, u64 size)
> 		memblock_remove(start, size);
> 	}
> 
>-	__release_memory_resource(start, size);
>+	release_mem_region_adjustable(&iomem_resource, start, size);
> 

Seems the only user of release_mem_region_adjustable() is here, can we move
iomem_resource into the function body? Actually, we don't iterate the resource
tree from any level. We always start from the root.

> 	try_offline_node(nid);
> 
>-- 
>2.26.2
David Hildenbrand Sept. 15, 2020, 7:35 a.m. UTC | #3
>> static int __ref try_remove_memory(int nid, u64 start, u64 size)
>> {
>> 	int rc = 0;
>> @@ -1777,7 +1757,7 @@ static int __ref try_remove_memory(int nid, u64 start, u64 size)
>> 		memblock_remove(start, size);
>> 	}
>>
>> -	__release_memory_resource(start, size);
>> +	release_mem_region_adjustable(&iomem_resource, start, size);
>>
> 
> Seems the only user of release_mem_region_adjustable() is here, can we move
> iomem_resource into the function body? Actually, we don't iterate the resource
> tree from any level. We always start from the root.

You mean, making iomem_resource implicit? I can spot that something
similar was done for

#define devm_release_mem_region(dev, start, n) \
	__devm_release_region(dev, &iomem_resource, (start), (n))

I'll send an addon patch for that, ok? - thanks.
Wei Yang Sept. 15, 2020, 9:06 a.m. UTC | #4
On Tue, Sep 15, 2020 at 09:35:30AM +0200, David Hildenbrand wrote:
>
>>> static int __ref try_remove_memory(int nid, u64 start, u64 size)
>>> {
>>> 	int rc = 0;
>>> @@ -1777,7 +1757,7 @@ static int __ref try_remove_memory(int nid, u64 start, u64 size)
>>> 		memblock_remove(start, size);
>>> 	}
>>>
>>> -	__release_memory_resource(start, size);
>>> +	release_mem_region_adjustable(&iomem_resource, start, size);
>>>
>> 
>> Seems the only user of release_mem_region_adjustable() is here, can we move
>> iomem_resource into the function body? Actually, we don't iterate the resource
>> tree from any level. We always start from the root.
>
>You mean, making iomem_resource implicit? I can spot that something
>similar was done for
>
>#define devm_release_mem_region(dev, start, n) \
>	__devm_release_region(dev, &iomem_resource, (start), (n))
>

What I prefer is remove iomem_resource from the parameter list. Just use is in
the function body.

For the example you listed, __release_region() would have varies of *parent*,
which looks reasonable to keep it here.

>I'll send an addon patch for that, ok? - thanks.
>
>-- 
>Thanks,
>
>David / dhildenb
David Hildenbrand Sept. 15, 2020, 9:15 a.m. UTC | #5
On 15.09.20 11:06, Wei Yang wrote:
> On Tue, Sep 15, 2020 at 09:35:30AM +0200, David Hildenbrand wrote:
>>
>>>> static int __ref try_remove_memory(int nid, u64 start, u64 size)
>>>> {
>>>> 	int rc = 0;
>>>> @@ -1777,7 +1757,7 @@ static int __ref try_remove_memory(int nid, u64 start, u64 size)
>>>> 		memblock_remove(start, size);
>>>> 	}
>>>>
>>>> -	__release_memory_resource(start, size);
>>>> +	release_mem_region_adjustable(&iomem_resource, start, size);
>>>>
>>>
>>> Seems the only user of release_mem_region_adjustable() is here, can we move
>>> iomem_resource into the function body? Actually, we don't iterate the resource
>>> tree from any level. We always start from the root.
>>
>> You mean, making iomem_resource implicit? I can spot that something
>> similar was done for
>>
>> #define devm_release_mem_region(dev, start, n) \
>> 	__devm_release_region(dev, &iomem_resource, (start), (n))
>>
> 
> What I prefer is remove iomem_resource from the parameter list. Just use is in
> the function body.
> 
> For the example you listed, __release_region() would have varies of *parent*,
> which looks reasonable to keep it here.

Yeah I got that ("making iomem_resource implicit"), as I said:

>> I'll send an addon patch for that, ok? - thanks.
Wei Yang Sept. 15, 2020, 9:33 a.m. UTC | #6
On Tue, Sep 15, 2020 at 11:15:53AM +0200, David Hildenbrand wrote:
>On 15.09.20 11:06, Wei Yang wrote:
>> On Tue, Sep 15, 2020 at 09:35:30AM +0200, David Hildenbrand wrote:
>>>
>>>>> static int __ref try_remove_memory(int nid, u64 start, u64 size)
>>>>> {
>>>>> 	int rc = 0;
>>>>> @@ -1777,7 +1757,7 @@ static int __ref try_remove_memory(int nid, u64 start, u64 size)
>>>>> 		memblock_remove(start, size);
>>>>> 	}
>>>>>
>>>>> -	__release_memory_resource(start, size);
>>>>> +	release_mem_region_adjustable(&iomem_resource, start, size);
>>>>>
>>>>
>>>> Seems the only user of release_mem_region_adjustable() is here, can we move
>>>> iomem_resource into the function body? Actually, we don't iterate the resource
>>>> tree from any level. We always start from the root.
>>>
>>> You mean, making iomem_resource implicit? I can spot that something
>>> similar was done for
>>>
>>> #define devm_release_mem_region(dev, start, n) \
>>> 	__devm_release_region(dev, &iomem_resource, (start), (n))
>>>
>> 
>> What I prefer is remove iomem_resource from the parameter list. Just use is in
>> the function body.
>> 
>> For the example you listed, __release_region() would have varies of *parent*,
>> which looks reasonable to keep it here.
>
>Yeah I got that ("making iomem_resource implicit"), as I said:
>

Thanks

>>> I'll send an addon patch for that, ok? - thanks.
>
>-- 
>Thanks,
>
>David / dhildenb
diff mbox series

Patch

diff --git a/include/linux/ioport.h b/include/linux/ioport.h
index 6c2b06fe8beb7..52a91f5fa1a36 100644
--- a/include/linux/ioport.h
+++ b/include/linux/ioport.h
@@ -248,8 +248,8 @@  extern struct resource * __request_region(struct resource *,
 extern void __release_region(struct resource *, resource_size_t,
 				resource_size_t);
 #ifdef CONFIG_MEMORY_HOTREMOVE
-extern int release_mem_region_adjustable(struct resource *, resource_size_t,
-				resource_size_t);
+extern void release_mem_region_adjustable(struct resource *, resource_size_t,
+					  resource_size_t);
 #endif
 
 /* Wrappers for managed devices */
diff --git a/kernel/resource.c b/kernel/resource.c
index f1175ce93a1d5..36b3552210120 100644
--- a/kernel/resource.c
+++ b/kernel/resource.c
@@ -1258,21 +1258,28 @@  EXPORT_SYMBOL(__release_region);
  *   assumes that all children remain in the lower address entry for
  *   simplicity.  Enhance this logic when necessary.
  */
-int release_mem_region_adjustable(struct resource *parent,
-				  resource_size_t start, resource_size_t size)
+void release_mem_region_adjustable(struct resource *parent,
+				   resource_size_t start, resource_size_t size)
 {
+	struct resource *new_res = NULL;
+	bool alloc_nofail = false;
 	struct resource **p;
 	struct resource *res;
-	struct resource *new_res;
 	resource_size_t end;
-	int ret = -EINVAL;
 
 	end = start + size - 1;
-	if ((start < parent->start) || (end > parent->end))
-		return ret;
+	if (WARN_ON_ONCE((start < parent->start) || (end > parent->end)))
+		return;
 
-	/* The alloc_resource() result gets checked later */
-	new_res = alloc_resource(GFP_KERNEL);
+	/*
+	 * We free up quite a lot of memory on memory hotunplug (esp., memap),
+	 * just before releasing the region. This is highly unlikely to
+	 * fail - let's play save and make it never fail as the caller cannot
+	 * perform any error handling (e.g., trying to re-add memory will fail
+	 * similarly).
+	 */
+retry:
+	new_res = alloc_resource(GFP_KERNEL | alloc_nofail ? __GFP_NOFAIL : 0);
 
 	p = &parent->child;
 	write_lock(&resource_lock);
@@ -1298,7 +1305,6 @@  int release_mem_region_adjustable(struct resource *parent,
 		 * so if we are dealing with them, let us just back off here.
 		 */
 		if (!(res->flags & IORESOURCE_SYSRAM)) {
-			ret = 0;
 			break;
 		}
 
@@ -1315,20 +1321,23 @@  int release_mem_region_adjustable(struct resource *parent,
 			/* free the whole entry */
 			*p = res->sibling;
 			free_resource(res);
-			ret = 0;
 		} else if (res->start == start && res->end != end) {
 			/* adjust the start */
-			ret = __adjust_resource(res, end + 1,
-						res->end - end);
+			WARN_ON_ONCE(__adjust_resource(res, end + 1,
+						       res->end - end));
 		} else if (res->start != start && res->end == end) {
 			/* adjust the end */
-			ret = __adjust_resource(res, res->start,
-						start - res->start);
+			WARN_ON_ONCE(__adjust_resource(res, res->start,
+						       start - res->start));
 		} else {
-			/* split into two entries */
+			/* split into two entries - we need a new resource */
 			if (!new_res) {
-				ret = -ENOMEM;
-				break;
+				new_res = alloc_resource(GFP_ATOMIC);
+				if (!new_res) {
+					alloc_nofail = true;
+					write_unlock(&resource_lock);
+					goto retry;
+				}
 			}
 			new_res->name = res->name;
 			new_res->start = end + 1;
@@ -1339,9 +1348,8 @@  int release_mem_region_adjustable(struct resource *parent,
 			new_res->sibling = res->sibling;
 			new_res->child = NULL;
 
-			ret = __adjust_resource(res, res->start,
-						start - res->start);
-			if (ret)
+			if (WARN_ON_ONCE(__adjust_resource(res, res->start,
+							   start - res->start)))
 				break;
 			res->sibling = new_res;
 			new_res = NULL;
@@ -1352,7 +1360,6 @@  int release_mem_region_adjustable(struct resource *parent,
 
 	write_unlock(&resource_lock);
 	free_resource(new_res);
-	return ret;
 }
 #endif	/* CONFIG_MEMORY_HOTREMOVE */
 
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index baded53b9ff92..4c47b68a9f4b5 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1724,26 +1724,6 @@  void try_offline_node(int nid)
 }
 EXPORT_SYMBOL(try_offline_node);
 
-static void __release_memory_resource(resource_size_t start,
-				      resource_size_t size)
-{
-	int ret;
-
-	/*
-	 * When removing memory in the same granularity as it was added,
-	 * this function never fails. It might only fail if resources
-	 * have to be adjusted or split. We'll ignore the error, as
-	 * removing of memory cannot fail.
-	 */
-	ret = release_mem_region_adjustable(&iomem_resource, start, size);
-	if (ret) {
-		resource_size_t endres = start + size - 1;
-
-		pr_warn("Unable to release resource <%pa-%pa> (%d)\n",
-			&start, &endres, ret);
-	}
-}
-
 static int __ref try_remove_memory(int nid, u64 start, u64 size)
 {
 	int rc = 0;
@@ -1777,7 +1757,7 @@  static int __ref try_remove_memory(int nid, u64 start, u64 size)
 		memblock_remove(start, size);
 	}
 
-	__release_memory_resource(start, size);
+	release_mem_region_adjustable(&iomem_resource, start, size);
 
 	try_offline_node(nid);