Re: [PATCH v4 4/5] mm: Fix page reference leak in soft_offline_page()
On Sun, Jan 17, 2021 at 2:01 PM Andrew Morton wrote:
>
> On Wed, 13 Jan 2021 16:43:32 -0800 Dan Williams
> wrote:
>
> > 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
> > Cc: Naoya Horiguchi
> > Cc: Michal Hocko
> > Reviewed-by: David Hildenbrand
> > Reviewed-by: Oscar Salvador
> > Cc:
> > Signed-off-by: Dan Williams
>
> A cc:stable patch in the middle is awkward. I'll make this a
> standalone patch for merging into mainline soon (for 5.11) and shall
> turn the rest into a 4-patch series, OK?
Sounds good to me.
Re: [PATCH v4 4/5] mm: Fix page reference leak in soft_offline_page()
On Wed, 13 Jan 2021 16:43:32 -0800 Dan Williams
wrote:
> 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
> Cc: Naoya Horiguchi
> Cc: Michal Hocko
> Reviewed-by: David Hildenbrand
> Reviewed-by: Oscar Salvador
> Cc:
> Signed-off-by: Dan Williams
A cc:stable patch in the middle is awkward. I'll make this a
standalone patch for merging into mainline soon (for 5.11) and shall
turn the rest into a 4-patch series, OK?
Re: [PATCH v4 4/5] mm: Fix page reference leak in soft_offline_page()
On Wed, Jan 13, 2021 at 10:18:09PM -0800, Dan Williams wrote:
> On Wed, Jan 13, 2021 at 5:50 PM HORIGUCHI NAOYA(堀口 直也)
> wrote:
> >
> > On Wed, Jan 13, 2021 at 04:43:32PM -0800, Dan Williams wrote:
> > > 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
> > > Cc: Naoya Horiguchi
> > > Cc: Michal Hocko
> > > Reviewed-by: David Hildenbrand
> > > Reviewed-by: Oscar Salvador
> > > Cc:
> > > Signed-off-by: Dan Williams
> >
> > I'm OK if we don't have any other better approach, but the proposed changes
> > make code a little messy, and I feel that get_user_pages() might be the
> > right place to fix. Is get_user_pages() expected to return struct page with
> > holding refcount for offline valid pages? I thought that such pages are
> > only used by drivers for dax-devices, but that might be wrong. Can I ask for
> > a little more explanation from this perspective?
>
> The motivation for ZONE_DEVICE is to allow get_user_pages() for "offline"
> pfns.
I missed this point, thank you.
>
> soft_offline_page() wants to only operate on "online" pfns.
Right.
>
> get_user_pages() on a dax-mapping returns an "offline" ZONE_DEVICE page.
OK.
>
> When pfn_to_online_page() fails the get_user_pages() reference needs
> to be dropped.
The background is clear to me, and I agree with this patch.
Reviewed-by: Naoya Horiguchi
>
> To be honest I dislike the entire flags based scheme for communicating
> the fact that page reference obtained by madvise needs to be dropped
> later. I'd rather pass a non-NULL 'struct page *' than redo
> pfn_to_page() conversions in the leaf functions, but that's a much
> larger change.
As Oscar mentions in another email, removing MF_COUNT_INCREASED was
recently discussed and rejected. I think that if pfn-page conversion
layer is somehow factored out from soft/hard offline handler, code would
be more readable/maintainable.
Thanks,
Naoya Horiguchi
Re: [PATCH v4 4/5] mm: Fix page reference leak in soft_offline_page()
On 2021-01-14 07:18, Dan Williams wrote: To be honest I dislike the entire flags based scheme for communicating the fact that page reference obtained by madvise needs to be dropped later. I'd rather pass a non-NULL 'struct page *' than redo pfn_to_page() conversions in the leaf functions, but that's a much larger change. We tried to remove that flag in the past but for different reasons. I will have another look to see what can be done. Thanks -- Oscar Salvador SUSE L3
Re: [PATCH v4 4/5] mm: Fix page reference leak in soft_offline_page()
On Wed, Jan 13, 2021 at 5:50 PM HORIGUCHI NAOYA(堀口 直也)
wrote:
>
> On Wed, Jan 13, 2021 at 04:43:32PM -0800, Dan Williams wrote:
> > 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
> > Cc: Naoya Horiguchi
> > Cc: Michal Hocko
> > Reviewed-by: David Hildenbrand
> > Reviewed-by: Oscar Salvador
> > Cc:
> > Signed-off-by: Dan Williams
>
> I'm OK if we don't have any other better approach, but the proposed changes
> make code a little messy, and I feel that get_user_pages() might be the
> right place to fix. Is get_user_pages() expected to return struct page with
> holding refcount for offline valid pages? I thought that such pages are
> only used by drivers for dax-devices, but that might be wrong. Can I ask for
> a little more explanation from this perspective?
The motivation for ZONE_DEVICE is to allow get_user_pages() for "offline" pfns.
soft_offline_page() wants to only operate on "online" pfns.
get_user_pages() on a dax-mapping returns an "offline" ZONE_DEVICE page.
When pfn_to_online_page() fails the get_user_pages() reference needs
to be dropped.
To be honest I dislike the entire flags based scheme for communicating
the fact that page reference obtained by madvise needs to be dropped
later. I'd rather pass a non-NULL 'struct page *' than redo
pfn_to_page() conversions in the leaf functions, but that's a much
larger change.
Re: [PATCH v4 4/5] mm: Fix page reference leak in soft_offline_page()
On Wed, Jan 13, 2021 at 04:43:32PM -0800, Dan Williams wrote:
> 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
> Cc: Naoya Horiguchi
> Cc: Michal Hocko
> Reviewed-by: David Hildenbrand
> Reviewed-by: Oscar Salvador
> Cc:
> Signed-off-by: Dan Williams
I'm OK if we don't have any other better approach, but the proposed changes
make code a little messy, and I feel that get_user_pages() might be the
right place to fix. Is get_user_pages() expected to return struct page with
holding refcount for offline valid pages? I thought that such pages are
only used by drivers for dax-devices, but that might be wrong. Can I ask for
a little more explanation from this perspective?
Thanks,
Naoya Horiguchi
> ---
> 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 v4 4/5] mm: Fix page reference leak in soft_offline_page()
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
Cc: Naoya Horiguchi
Cc: Michal Hocko
Reviewed-by: David Hildenbrand
Reviewed-by: Oscar Salvador
Cc:
Signed-off-by: Dan Williams
---
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;
}
