| Message ID | 20241024032300.2501949-1-cuigaosheng1@huawei.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [-next] mm/ksm: Add missing IS_ERR_OR_NULL check for stable_tree_search() | expand |
On 24.10.24 05:23, Gaosheng Cui wrote: > The stable_tree_search() maybe return -EBUSY if the stable node's page > is being migrated or nullptr, we need to check kfolio with > IS_ERR_OR_NULL() before dereference it. > > To mitigate this, add IS_ERR_OR_NULL check for stable_tree_search(). > > Fixes: 15605244fdce ("ksm: convert cmp_and_merge_page() to use a folio") > Signed-off-by: Gaosheng Cui <cuigaosheng1@huawei.com> > --- > mm/ksm.c | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > diff --git a/mm/ksm.c b/mm/ksm.c > index 4d482d011745..7ac59cde626c 100644 > --- a/mm/ksm.c > +++ b/mm/ksm.c > @@ -1787,7 +1787,7 @@ static __always_inline struct folio *chain(struct ksm_stable_node **s_n_d, > * with identical content to the page that we are scanning right now. > * > * This function returns the stable tree node of identical content if found, > - * NULL otherwise. > + * -EBUSY if the stable node's page is being migrated, NULL otherwise. > */ > static struct folio *stable_tree_search(struct page *page) > { > @@ -2261,7 +2261,8 @@ static void cmp_and_merge_page(struct page *page, struct ksm_rmap_item *rmap_ite > > /* Start by searching for the folio in the stable tree */ > kfolio = stable_tree_search(page); > - if (&kfolio->page == page && rmap_item->head == stable_node) { > + if (!IS_ERR_OR_NULL(kfolio) && &kfolio->page == page && > + rmap_item->head == stable_node) { > folio_put(kfolio); > return; > } I'm late, but LGTM Acked-by: David Hildenbrand <david@redhat.com>
On Fri, Nov 15, 2024 at 11:44:10AM +0100, David Hildenbrand wrote: > On 24.10.24 05:23, Gaosheng Cui wrote: > > The stable_tree_search() maybe return -EBUSY if the stable node's page > > is being migrated or nullptr, we need to check kfolio with > > IS_ERR_OR_NULL() before dereference it. Argh. I doidn't notice this when it came through. Andrew already folded it in, but it's utter garbage. We don't dereference folio. NAK.
On 15.11.24 16:41, Matthew Wilcox wrote: > On Fri, Nov 15, 2024 at 11:44:10AM +0100, David Hildenbrand wrote: >> On 24.10.24 05:23, Gaosheng Cui wrote: >>> The stable_tree_search() maybe return -EBUSY if the stable node's page >>> is being migrated or nullptr, we need to check kfolio with >>> IS_ERR_OR_NULL() before dereference it. > > Argh. I doidn't notice this when it came through. Andrew already > folded it in, but it's utter garbage. We don't dereference folio. > NAK. Ah, &kfolio->page indeed doesn't de-reference. I was blindly assuming someone actually ran into an issue here. Thanks for double-checking ...
diff --git a/mm/ksm.c b/mm/ksm.c index 4d482d011745..7ac59cde626c 100644 --- a/mm/ksm.c +++ b/mm/ksm.c @@ -1787,7 +1787,7 @@ static __always_inline struct folio *chain(struct ksm_stable_node **s_n_d, * with identical content to the page that we are scanning right now. * * This function returns the stable tree node of identical content if found, - * NULL otherwise. + * -EBUSY if the stable node's page is being migrated, NULL otherwise. */ static struct folio *stable_tree_search(struct page *page) { @@ -2261,7 +2261,8 @@ static void cmp_and_merge_page(struct page *page, struct ksm_rmap_item *rmap_ite /* Start by searching for the folio in the stable tree */ kfolio = stable_tree_search(page); - if (&kfolio->page == page && rmap_item->head == stable_node) { + if (!IS_ERR_OR_NULL(kfolio) && &kfolio->page == page && + rmap_item->head == stable_node) { folio_put(kfolio); return; }
The stable_tree_search() maybe return -EBUSY if the stable node's page is being migrated or nullptr, we need to check kfolio with IS_ERR_OR_NULL() before dereference it. To mitigate this, add IS_ERR_OR_NULL check for stable_tree_search(). Fixes: 15605244fdce ("ksm: convert cmp_and_merge_page() to use a folio") Signed-off-by: Gaosheng Cui <cuigaosheng1@huawei.com> --- mm/ksm.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-)