| Message ID | 20210914114508.23725-1-linmiaohe@huawei.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [v3] mm/page_isolation: guard against possible putback unisolated page | expand |
On 14.09.21 13:45, Miaohe Lin wrote: > Isolating a free page in an isolated pageblock is expected to always work > as watermarks don't apply here. But if __isolate_free_page() failed, due > to condition changes, the page will be left on the free list. And the page > will be put back to free list again via __putback_isolated_page(). This may > trigger VM_BUG_ON_PAGE() on page->flags checking in __free_one_page() if > PageReported is set. Or we will corrupt the free list because list_add() > will be called for pages already on another list. Add a VM_WARN_ON() to > complain about this change. > > Signed-off-by: Miaohe Lin <linmiaohe@huawei.com> > --- > v1->v2: > Add VM_WARN_ON to catch unexpected isolating failure. > v2->v3: > Change the patch description+subject and remove Fixes. > --- > mm/page_isolation.c | 9 +++++++-- > 1 file changed, 7 insertions(+), 2 deletions(-) > > diff --git a/mm/page_isolation.c b/mm/page_isolation.c > index f93cc63d8fa1..f67c4c70f17f 100644 > --- a/mm/page_isolation.c > +++ b/mm/page_isolation.c > @@ -94,8 +94,13 @@ static void unset_migratetype_isolate(struct page *page, unsigned migratetype) > buddy = page + (buddy_pfn - pfn); > > if (!is_migrate_isolate_page(buddy)) { > - __isolate_free_page(page, order); > - isolated_page = true; > + isolated_page = !!__isolate_free_page(page, order); > + /* > + * Isolating a free page in an isolated pageblock > + * is expected to always work as watermarks don't > + * apply here. > + */ > + VM_WARN_ON(!isolated_page); > } > } > } > Reviewed-by: David Hildenbrand <david@redhat.com>
On 9/14/21 13:45, Miaohe Lin wrote: > Isolating a free page in an isolated pageblock is expected to always work > as watermarks don't apply here. But if __isolate_free_page() failed, due > to condition changes, the page will be left on the free list. And the page > will be put back to free list again via __putback_isolated_page(). This may > trigger VM_BUG_ON_PAGE() on page->flags checking in __free_one_page() if > PageReported is set. Or we will corrupt the free list because list_add() > will be called for pages already on another list. Add a VM_WARN_ON() to > complain about this change. > > Signed-off-by: Miaohe Lin <linmiaohe@huawei.com> Acked-by: Vlastimil Babka <vbabka@suse.cz> > --- > v1->v2: > Add VM_WARN_ON to catch unexpected isolating failure. > v2->v3: > Change the patch description+subject and remove Fixes. > --- > mm/page_isolation.c | 9 +++++++-- > 1 file changed, 7 insertions(+), 2 deletions(-) > > diff --git a/mm/page_isolation.c b/mm/page_isolation.c > index f93cc63d8fa1..f67c4c70f17f 100644 > --- a/mm/page_isolation.c > +++ b/mm/page_isolation.c > @@ -94,8 +94,13 @@ static void unset_migratetype_isolate(struct page *page, unsigned migratetype) > buddy = page + (buddy_pfn - pfn); > > if (!is_migrate_isolate_page(buddy)) { > - __isolate_free_page(page, order); > - isolated_page = true; > + isolated_page = !!__isolate_free_page(page, order); > + /* > + * Isolating a free page in an isolated pageblock > + * is expected to always work as watermarks don't > + * apply here. > + */ > + VM_WARN_ON(!isolated_page); > } > } > } >
On Tue, 14 Sep 2021 19:45:08 +0800 Miaohe Lin <linmiaohe@huawei.com> wrote: > Isolating a free page in an isolated pageblock is expected to always work > as watermarks don't apply here. But if __isolate_free_page() failed, due > to condition changes, the page will be left on the free list. And the page > will be put back to free list again via __putback_isolated_page(). This may > trigger VM_BUG_ON_PAGE() on page->flags checking in __free_one_page() if > PageReported is set. Or we will corrupt the free list because list_add() > will be called for pages already on another list. Add a VM_WARN_ON() to > complain about this change. Are you able to identify a Fixes: here? Is a cc:stable justified?
On 2021/9/15 10:09, Andrew Morton wrote: > On Tue, 14 Sep 2021 19:45:08 +0800 Miaohe Lin <linmiaohe@huawei.com> wrote: > >> Isolating a free page in an isolated pageblock is expected to always work >> as watermarks don't apply here. But if __isolate_free_page() failed, due >> to condition changes, the page will be left on the free list. And the page >> will be put back to free list again via __putback_isolated_page(). This may >> trigger VM_BUG_ON_PAGE() on page->flags checking in __free_one_page() if >> PageReported is set. Or we will corrupt the free list because list_add() >> will be called for pages already on another list. Add a VM_WARN_ON() to >> complain about this change. > > Are you able to identify a Fixes: here? > Sure, this should be "Fixes: 3c605096d315 ("mm/page_alloc: restrict max order of merging on isolated pageblock")." > Is a cc:stable justified? I'm afraid not. As David pointed out, "" In unset_migratetype_isolate() we check that is_migrate_isolate_page(page) holds, otherwise we return. We call __isolate_free_page() only for such pages. __isolate_free_page() won't perform watermark checks on is_migrate_isolate(). Consequently, __isolate_free_page() should never fail when called from unset_migratetype_isolate() "" In a nutshell, __isolate_free_page can not fail here. So it is harmless now and doesn't worth cc:stable. Please see https://www.spinics.net/lists/linux-mm/msg269434.html for detail. Many thanks. > . >
diff --git a/mm/page_isolation.c b/mm/page_isolation.c index f93cc63d8fa1..f67c4c70f17f 100644 --- a/mm/page_isolation.c +++ b/mm/page_isolation.c @@ -94,8 +94,13 @@ static void unset_migratetype_isolate(struct page *page, unsigned migratetype) buddy = page + (buddy_pfn - pfn); if (!is_migrate_isolate_page(buddy)) { - __isolate_free_page(page, order); - isolated_page = true; + isolated_page = !!__isolate_free_page(page, order); + /* + * Isolating a free page in an isolated pageblock + * is expected to always work as watermarks don't + * apply here. + */ + VM_WARN_ON(!isolated_page); } } }
Isolating a free page in an isolated pageblock is expected to always work as watermarks don't apply here. But if __isolate_free_page() failed, due to condition changes, the page will be left on the free list. And the page will be put back to free list again via __putback_isolated_page(). This may trigger VM_BUG_ON_PAGE() on page->flags checking in __free_one_page() if PageReported is set. Or we will corrupt the free list because list_add() will be called for pages already on another list. Add a VM_WARN_ON() to complain about this change. Signed-off-by: Miaohe Lin <linmiaohe@huawei.com> --- v1->v2: Add VM_WARN_ON to catch unexpected isolating failure. v2->v3: Change the patch description+subject and remove Fixes. --- mm/page_isolation.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-)