[PATCH v3 0/6] mm: Fix pfn_to_online_page() with respect to ZONE_DEVICE

[PATCH v3 0/6] mm: Fix pfn_to_online_page() with respect to ZONE_DEVICE

[Dan Williams]

Changes since v2 [1]:
- Collect some reviewed-by's from David and Oscar

- Rework subsection validity to include pfn_valid() gated by
  CONFIG_HAVE_ARCH_PFN_VALID (David, Oscar)

- Introduce pgmap_pfn_valid() to validate metadata vs data in a pgmap (David)

! Kill put_ref_page(): the extra "if (ref_page) put_page(ref_page)" still
  feels more cluttered than adding a tiny helper. (Oscar)

[1]: http://lore.kernel.org/r/161044407603.1482714.16630477578392768273.stgit@dwillia2-desk3.amr.corp.intel.com

---

Michal reminds that the discussion about how to ensure pfn-walkers do
not get confused by ZONE_DEVICE pages never resolved. A pfn-walker that
uses pfn_to_online_page() may inadvertently translate a pfn as online
and in the page allocator, when it is offline managed by a ZONE_DEVICE
mapping (details in Patch 3: ("mm: Teach pfn_to_online_page() about
ZONE_DEVICE section collisions")).

The 2 proposals under consideration are teach pfn_to_online_page() to be
precise in the presence of mixed-zone sections, or teach the memory-add
code to drop the System RAM associated with ZONE_DEVICE collisions. In
order to not regress memory capacity by a few 10s to 100s of MiB the
approach taken in this set is to add precision to pfn_to_online_page().

In the course of validating pfn_to_online_page() a couple other fixes
fell out:

1/ soft_offline_page() fails to drop the reference taken in the
   madvise(..., MADV_SOFT_OFFLINE) case.

2/ The libnvdimm sysfs attribute visibility code was failing to publish
   the resource base for memmap=ss!nn defined namespaces. This is needed
   for the regression test for soft_offline_page().

3/ memory_failure() uses get_dev_pagemap() to lookup ZONE_DEVICE pages,
   however that mapping may contain data pages and metadata raw pfns.
   Introduce pgmap_pfn_valid() to delineate the 2 types and fail the
   handling of raw metadata pfns.

---

Dan Williams (6):
      mm: Move pfn_to_online_page() out of line
      mm: Teach pfn_to_online_page() to consider subsection validity
      mm: Teach pfn_to_online_page() about ZONE_DEVICE section collisions
      mm: Fix page reference leak in soft_offline_page()
      mm: Fix memory_failure() handling of dax-namespace metadata
      libnvdimm/namespace: Fix visibility of namespace resource attribute


 drivers/nvdimm/namespace_devs.c |   10 +++---
 include/linux/memory_hotplug.h  |   17 +--------
 include/linux/memremap.h        |    6 +++
 include/linux/mmzone.h          |   22 ++++++++----
 mm/memory-failure.c             |   26 ++++++++++++--
 mm/memory_hotplug.c             |   70 +++++++++++++++++++++++++++++++++++++++
 mm/memremap.c                   |   15 ++++++++
 7 files changed, 134 insertions(+), 32 deletions(-)

[PATCH v3 4/6] mm: Fix page reference leak in soft_offline_page()

[Dan Williams]

The conversion to move pfn_to_online_page() internal to
soft_offline_page() missed that the get_user_pages() reference taken by
the madvise() path needs to be dropped when pfn_to_online_page() fails.
Note the direct sysfs-path to soft_offline_page() does not perform a
get_user_pages() lookup.

When soft_offline_page() is handed a pfn_valid() &&
!pfn_to_online_page() pfn the kernel hangs at dax-device shutdown due to
a leaked reference.

Fixes: feec24a6139d ("mm, soft-offline: convert parameter to pfn")
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Naoya Horiguchi <nao.horiguchi@gmail.com>
Cc: Michal Hocko <mhocko@kernel.org>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
Cc: <stable@vger.kernel.org>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
 mm/memory-failure.c |   20 ++++++++++++++++----
 1 file changed, 16 insertions(+), 4 deletions(-)

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 5a38e9eade94..78b173c7190c 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -1885,6 +1885,12 @@ static int soft_offline_free_page(struct page *page)
 	return rc;
 }
 
+static void put_ref_page(struct page *page)
+{
+	if (page)
+		put_page(page);
+}
+
 /**
  * soft_offline_page - Soft offline a page.
  * @pfn: pfn to soft-offline
@@ -1910,20 +1916,26 @@ static int soft_offline_free_page(struct page *page)
 int soft_offline_page(unsigned long pfn, int flags)
 {
 	int ret;
-	struct page *page;
 	bool try_again = true;
+	struct page *page, *ref_page = NULL;
+
+	WARN_ON_ONCE(!pfn_valid(pfn) && (flags & MF_COUNT_INCREASED));
 
 	if (!pfn_valid(pfn))
 		return -ENXIO;
+	if (flags & MF_COUNT_INCREASED)
+		ref_page = pfn_to_page(pfn);
+
 	/* Only online pages can be soft-offlined (esp., not ZONE_DEVICE). */
 	page = pfn_to_online_page(pfn);
-	if (!page)
+	if (!page) {
+		put_ref_page(ref_page);
 		return -EIO;
+	}
 
 	if (PageHWPoison(page)) {
 		pr_info("%s: %#lx page already poisoned\n", __func__, pfn);
-		if (flags & MF_COUNT_INCREASED)
-			put_page(page);
+		put_ref_page(ref_page);
 		return 0;
 	}
 

[PATCH v3 6/6] libnvdimm/namespace: Fix visibility of namespace resource attribute

[Dan Williams]

Legacy pmem namespaces lost support for the "resource" attribute when
the code was cleaned up to put the permission visibility in the
declaration. Restore this by listing 'resource' in the default
attributes.

A new ndctl regression test for pfn_to_online_page() corner cases builds
on this fix.

Fixes: bfd2e9140656 ("libnvdimm: Simplify root read-only definition for the 'resource' attribute")
Cc: Vishal Verma <vishal.l.verma@intel.com>
Cc: Dave Jiang <dave.jiang@intel.com>
Cc: Ira Weiny <ira.weiny@intel.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
 drivers/nvdimm/namespace_devs.c |   10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/drivers/nvdimm/namespace_devs.c b/drivers/nvdimm/namespace_devs.c
index 6da67f4d641a..2403b71b601e 100644
--- a/drivers/nvdimm/namespace_devs.c
+++ b/drivers/nvdimm/namespace_devs.c
@@ -1635,11 +1635,11 @@ static umode_t namespace_visible(struct kobject *kobj,
 		return a->mode;
 	}
 
-	if (a == &dev_attr_nstype.attr || a == &dev_attr_size.attr
-			|| a == &dev_attr_holder.attr
-			|| a == &dev_attr_holder_class.attr
-			|| a == &dev_attr_force_raw.attr
-			|| a == &dev_attr_mode.attr)
+	/* base is_namespace_io() attributes */
+	if (a == &dev_attr_nstype.attr || a == &dev_attr_size.attr ||
+	    a == &dev_attr_holder.attr || a == &dev_attr_holder_class.attr ||
+	    a == &dev_attr_force_raw.attr || a == &dev_attr_mode.attr ||
+	    a == &dev_attr_resource.attr)
 		return a->mode;
 
 	return 0;

Re: [PATCH v3 6/6] libnvdimm/namespace: Fix visibility of namespace resource attribute

[Greg KH]

On Tue, Jan 12, 2021 at 11:35:50PM -0800, Dan Williams wrote:
> Legacy pmem namespaces lost support for the "resource" attribute when
> the code was cleaned up to put the permission visibility in the
> declaration. Restore this by listing 'resource' in the default
> attributes.
> 
> A new ndctl regression test for pfn_to_online_page() corner cases builds
> on this fix.
> 
> Fixes: bfd2e9140656 ("libnvdimm: Simplify root read-only definition for the 'resource' attribute")
> Cc: Vishal Verma <vishal.l.verma@intel.com>
> Cc: Dave Jiang <dave.jiang@intel.com>
> Cc: Ira Weiny <ira.weiny@intel.com>
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
> ---
>  drivers/nvdimm/namespace_devs.c |   10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)

<formletter>

This is not the correct way to submit patches for inclusion in the
stable kernel tree.  Please read:
    https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
for how to do this properly.

</formletter>