Andrew, Could you please drop this from mm tree. I will have to raise PATCH V4 here. Thanks, Charan On 8/10/2022 7:27 AM, Andrew Morton wrote: > > The patch titled > Subject: mm: fix use-after free of page_ext after race with memory-offline > has been added to the -mm mm-unstable branch. Its filename is > mm-fix-use-after-free-of-page_ext-after-race-with-memory-offline.patch > > This patch will shortly appear at > https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-fix-use-after-free-of-page_ext-after-race-with-memory-offline.patch > > This patch will later appear in the mm-unstable branch at > git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm > > Before you just go and hit "reply", please: > a) Consider who else should be cc'ed > b) Prefer to cc a suitable mailing list as well > c) Ideally: find the original patch on the mailing list and do a > reply-to-all to that, adding suitable additional cc's > > *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** > > The -mm tree is included into linux-next via the mm-everything > branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm > and is updated there every 2-3 working days > > ------------------------------------------------------ > From: Charan Teja Kalla <quic_charante@xxxxxxxxxxx> > Subject: mm: fix use-after free of page_ext after race with memory-offline > Date: Tue, 9 Aug 2022 20:16:43 +0530 > > The below is one path where race between page_ext and offline of the > respective memory blocks will cause use-after-free on the access of > page_ext structure. > > process1 process2 > --------- --------- > a)doing /proc/page_owner doing memory offline > through offline_pages. > > b)PageBuddy check is failed > thus proceed to get the > page_owner information > through page_ext access. > page_ext = lookup_page_ext(page); > > migrate_pages(); > ................. > Since all pages are successfully > migrated as part of the offline > operation,send MEM_OFFLINE notification > where for page_ext it calls: > offline_page_ext()--> > __free_page_ext()--> > free_page_ext()--> > vfree(ms->page_ext) > mem_section->page_ext = NULL > > c) Check for the PAGE_EXT flags > in the page_ext->flags access > results into the use-after-free(leading > to the translation faults). > > As mentioned above, there is really no synchronization between page_ext > access and its freeing in the memory_offline. > > The memory offline steps(roughly) on a memory block is as below: > 1) Isolate all the pages > 2) while(1) > try free the pages to buddy.(->free_list[MIGRATE_ISOLATE]) > 3) delete the pages from this buddy list. > 4) Then free page_ext.(Note: The struct page is still alive as it is > freed only during hot remove of the memory which frees the memmap, which > steps the user might not perform). > > This design leads to the state where struct page is alive but the struct > page_ext is freed, where the later is ideally part of the former which > just representing the page_flags (check [3] for why this design is > chosen). > > The above mentioned race is just one example __but the problem persists in > the other paths too involving page_ext->flags access(eg: > page_is_idle())__. Since offline waits till the last reference on the > page goes down i.e. any path that took the refcount on the page can make > the memory offline operation to wait. Eg: In the migrate_pages() > operation, we do take the extra refcount on the pages that are under > migration and then we do copy page_owner by accessing page_ext. > > Fix those paths where offline races with page_ext access by maintaining > synchronization with rcu lock and is achieved in 3 steps: 1) Invalidate > all the page_ext's of the sections of a memory block by storing a flag in > the LSB of mem_section->page_ext. > > 2) Wait till all the existing readers to finish working with the > ->page_ext's with synchronize_rcu(). Any parallel process that starts > after this call will not get page_ext, through lookup_page_ext(), for > the block parallel offline operation is being performed. > > 3) Now safely free all sections ->page_ext's of the block on which > offline operation is being performed. > > Note: If synchronize_rcu() takes time then optimizations can be done in > this path through call_rcu()[2]. > > Thanks to David Hildenbrand for his views/suggestions on the initial > discussion[1] and Pavan kondeti for various inputs on this patch. > > [1] https://lore.kernel.org/linux-mm/59edde13-4167-8550-86f0-11fc67882107@xxxxxxxxxxx/ > [2] https://lore.kernel.org/all/a26ce299-aed1-b8ad-711e-a49e82bdd180@xxxxxxxxxxx/T/#u > [3] https://lore.kernel.org/all/6fa6b7aa-731e-891c-3efb-a03d6a700efa@xxxxxxxxxx/ > > Link: https://lkml.kernel.org/r/1660056403-20894-1-git-send-email-quic_charante@xxxxxxxxxxx > Signed-off-by: Charan Teja Kalla <quic_charante@xxxxxxxxxxx> > Suggested-by: David Hildenbrand <david@xxxxxxxxxx> > Suggested-by: Michal Hocko <mhocko@xxxxxxxx> > Cc: Pasha Tatashin <pasha.tatashin@xxxxxxxxxx> > Cc: Fernand Sieber <sieberf@xxxxxxxxxx> > Cc: Shakeel Butt <shakeelb@xxxxxxxxxx> > Cc: SeongJae Park <sjpark@xxxxxxxxx> > Cc: David Howells <dhowells@xxxxxxxxxx> > Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx> > Cc: Pavan Kondeti <quic_pkondeti@xxxxxxxxxxx> > Cc: Charan Teja Kalla <quic_charante@xxxxxxxxxxx> > Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > --- > > include/linux/page_ext.h | 17 ++++-- > include/linux/page_idle.h | 34 +++++++++---- > mm/page_ext.c | 92 +++++++++++++++++++++++++++++++++--- > mm/page_owner.c | 74 +++++++++++++++++++++------- > mm/page_table_check.c | 10 ++- > 5 files changed, 184 insertions(+), 43 deletions(-) > > --- a/include/linux/page_ext.h~mm-fix-use-after-free-of-page_ext-after-race-with-memory-offline > +++ a/include/linux/page_ext.h > @@ -55,7 +55,8 @@ static inline void page_ext_init(void) > } > #endif > > -struct page_ext *lookup_page_ext(const struct page *page); > +extern struct page_ext *page_ext_get(struct page *page); > +extern void page_ext_put(void); > > static inline struct page_ext *page_ext_next(struct page_ext *curr) > { > @@ -71,11 +72,6 @@ static inline void pgdat_page_ext_init(s > { > } > > -static inline struct page_ext *lookup_page_ext(const struct page *page) > -{ > - return NULL; > -} > - > static inline void page_ext_init(void) > { > } > @@ -87,5 +83,14 @@ static inline void page_ext_init_flatmem > static inline void page_ext_init_flatmem(void) > { > } > + > +static inline struct page *page_ext_get(struct page *page) > +{ > + return NULL; > +} > + > +static inline void page_ext_put(void) > +{ > +} > #endif /* CONFIG_PAGE_EXTENSION */ > #endif /* __LINUX_PAGE_EXT_H */ > --- a/include/linux/page_idle.h~mm-fix-use-after-free-of-page_ext-after-race-with-memory-offline > +++ a/include/linux/page_idle.h > @@ -13,65 +13,79 @@ > * If there is not enough space to store Idle and Young bits in page flags, use > * page ext flags instead. > */ > - > static inline bool folio_test_young(struct folio *folio) > { > - struct page_ext *page_ext = lookup_page_ext(&folio->page); > + struct page_ext *page_ext = page_ext_get(&folio->page); > + bool page_young; > > if (unlikely(!page_ext)) > return false; > > - return test_bit(PAGE_EXT_YOUNG, &page_ext->flags); > + page_young = test_bit(PAGE_EXT_YOUNG, &page_ext->flags); > + page_ext_put(); > + > + return page_young; > } > > static inline void folio_set_young(struct folio *folio) > { > - struct page_ext *page_ext = lookup_page_ext(&folio->page); > + struct page_ext *page_ext = page_ext_get(&folio->page); > > if (unlikely(!page_ext)) > return; > > set_bit(PAGE_EXT_YOUNG, &page_ext->flags); > + page_ext_put(); > } > > static inline bool folio_test_clear_young(struct folio *folio) > { > - struct page_ext *page_ext = lookup_page_ext(&folio->page); > + struct page_ext *page_ext = page_ext_get(&folio->page); > + bool page_young; > > if (unlikely(!page_ext)) > return false; > > - return test_and_clear_bit(PAGE_EXT_YOUNG, &page_ext->flags); > + page_young = test_and_clear_bit(PAGE_EXT_YOUNG, &page_ext->flags); > + page_ext_put(); > + > + return page_young; > } > > static inline bool folio_test_idle(struct folio *folio) > { > - struct page_ext *page_ext = lookup_page_ext(&folio->page); > + struct page_ext *page_ext = page_ext_get(&folio->page); > + bool page_idle; > > if (unlikely(!page_ext)) > return false; > > - return test_bit(PAGE_EXT_IDLE, &page_ext->flags); > + page_idle = test_bit(PAGE_EXT_IDLE, &page_ext->flags); > + page_ext_put(); > + > + return page_idle; > } > > static inline void folio_set_idle(struct folio *folio) > { > - struct page_ext *page_ext = lookup_page_ext(&folio->page); > + struct page_ext *page_ext = page_ext_get(&folio->page); > > if (unlikely(!page_ext)) > return; > > set_bit(PAGE_EXT_IDLE, &page_ext->flags); > + page_ext_put(); > } > > static inline void folio_clear_idle(struct folio *folio) > { > - struct page_ext *page_ext = lookup_page_ext(&folio->page); > + struct page_ext *page_ext = page_ext_get(&folio->page); > > if (unlikely(!page_ext)) > return; > > clear_bit(PAGE_EXT_IDLE, &page_ext->flags); > + page_ext_put(); > } > #endif /* !CONFIG_64BIT */ > > --- a/mm/page_ext.c~mm-fix-use-after-free-of-page_ext-after-race-with-memory-offline > +++ a/mm/page_ext.c > @@ -9,6 +9,7 @@ > #include <linux/page_owner.h> > #include <linux/page_idle.h> > #include <linux/page_table_check.h> > +#include <linux/rcupdate.h> > > /* > * struct page extension > @@ -59,6 +60,10 @@ > * can utilize this callback to initialize the state of it correctly. > */ > > +#ifdef CONFIG_SPARSEMEM > +#define PAGE_EXT_INVALID (0x1) > +#endif > + > #if defined(CONFIG_PAGE_IDLE_FLAG) && !defined(CONFIG_64BIT) > static bool need_page_idle(void) > { > @@ -84,6 +89,7 @@ static struct page_ext_operations *page_ > unsigned long page_ext_size = sizeof(struct page_ext); > > static unsigned long total_usage; > +static struct page_ext *lookup_page_ext(const struct page *page); > > static bool __init invoke_need_callbacks(void) > { > @@ -125,6 +131,37 @@ static inline struct page_ext *get_entry > return base + page_ext_size * index; > } > > +/* > + * This function gives proper page_ext of a memory section > + * during race with the offline operation on a memory block > + * this section falls into. Not using this function to get > + * page_ext of a page, in code paths where extra refcount > + * is not taken on that page eg: pfn walking, can lead to > + * use-after-free access of page_ext. > + */ > +struct page_ext *page_ext_get(struct page *page) > +{ > + struct page_ext *page_ext; > + > + rcu_read_lock(); > + page_ext = lookup_page_ext(page); > + if (!page_ext) { > + rcu_read_unlock(); > + return NULL; > + } > + > + return page_ext; > +} > + > +/* > + * Must be called after work is done with the page_ext received > + * with page_ext_get(). > + */ > + > +void page_ext_put(void) > +{ > + rcu_read_unlock(); > +} > #ifndef CONFIG_SPARSEMEM > > > @@ -133,12 +170,13 @@ void __meminit pgdat_page_ext_init(struc > pgdat->node_page_ext = NULL; > } > > -struct page_ext *lookup_page_ext(const struct page *page) > +static struct page_ext *lookup_page_ext(const struct page *page) > { > unsigned long pfn = page_to_pfn(page); > unsigned long index; > struct page_ext *base; > > + WARN_ON_ONCE(!rcu_read_lock_held()); > base = NODE_DATA(page_to_nid(page))->node_page_ext; > /* > * The sanity checks the page allocator does upon freeing a > @@ -206,20 +244,27 @@ fail: > } > > #else /* CONFIG_SPARSEMEM */ > +static bool page_ext_invalid(struct page_ext *page_ext) > +{ > + return !page_ext || (((unsigned long)page_ext & PAGE_EXT_INVALID) == PAGE_EXT_INVALID); > +} > > -struct page_ext *lookup_page_ext(const struct page *page) > +static struct page_ext *lookup_page_ext(const struct page *page) > { > unsigned long pfn = page_to_pfn(page); > struct mem_section *section = __pfn_to_section(pfn); > + struct page_ext *page_ext = READ_ONCE(section->page_ext); > + > + WARN_ON_ONCE(!rcu_read_lock_held()); > /* > * The sanity checks the page allocator does upon freeing a > * page can reach here before the page_ext arrays are > * allocated when feeding a range of pages to the allocator > * for the first time during bootup or memory hotplug. > */ > - if (!section->page_ext) > + if (page_ext_invalid(page_ext)) > return NULL; > - return get_entry(section->page_ext, pfn); > + return get_entry(page_ext, pfn); > } > > static void *__meminit alloc_page_ext(size_t size, int nid) > @@ -298,9 +343,30 @@ static void __free_page_ext(unsigned lon > ms = __pfn_to_section(pfn); > if (!ms || !ms->page_ext) > return; > - base = get_entry(ms->page_ext, pfn); > + > + base = READ_ONCE(ms->page_ext); > + /* > + * page_ext here can be valid while doing the roll back > + * operation in online_page_ext(). > + */ > + if (page_ext_invalid(base)) > + base = (void *)base - PAGE_EXT_INVALID; > + WRITE_ONCE(ms->page_ext, NULL); > + > + base = get_entry(base, pfn); > free_page_ext(base); > - ms->page_ext = NULL; > +} > + > +static void __invalidate_page_ext(unsigned long pfn) > +{ > + struct mem_section *ms; > + void *val; > + > + ms = __pfn_to_section(pfn); > + if (!ms || !ms->page_ext) > + return; > + val = (void *)ms->page_ext + PAGE_EXT_INVALID; > + WRITE_ONCE(ms->page_ext, val); > } > > static int __meminit online_page_ext(unsigned long start_pfn, > @@ -343,6 +409,20 @@ static int __meminit offline_page_ext(un > start = SECTION_ALIGN_DOWN(start_pfn); > end = SECTION_ALIGN_UP(start_pfn + nr_pages); > > + /* > + * Freeing of page_ext is done in 3 steps to avoid > + * use-after-free of it: > + * 1) Traverse all the sections and mark their page_ext > + * as invalid. > + * 2) Wait for all the existing users of page_ext who > + * started before invalidation to finish. > + * 3) Free the page_ext. > + */ > + for (pfn = start; pfn < end; pfn += PAGES_PER_SECTION) > + __invalidate_page_ext(pfn); > + > + synchronize_rcu(); > + > for (pfn = start; pfn < end; pfn += PAGES_PER_SECTION) > __free_page_ext(pfn); > return 0; > --- a/mm/page_owner.c~mm-fix-use-after-free-of-page_ext-after-race-with-memory-offline > +++ a/mm/page_owner.c > @@ -141,7 +141,7 @@ void __reset_page_owner(struct page *pag > struct page_owner *page_owner; > u64 free_ts_nsec = local_clock(); > > - page_ext = lookup_page_ext(page); > + page_ext = page_ext_get(page); > if (unlikely(!page_ext)) > return; > > @@ -153,6 +153,7 @@ void __reset_page_owner(struct page *pag > page_owner->free_ts_nsec = free_ts_nsec; > page_ext = page_ext_next(page_ext); > } > + page_ext_put(); > } > > static inline void __set_page_owner_handle(struct page_ext *page_ext, > @@ -183,19 +184,26 @@ static inline void __set_page_owner_hand > noinline void __set_page_owner(struct page *page, unsigned short order, > gfp_t gfp_mask) > { > - struct page_ext *page_ext = lookup_page_ext(page); > + struct page_ext *page_ext = page_ext_get(page); > depot_stack_handle_t handle; > > if (unlikely(!page_ext)) > return; > + page_ext_put(); > > handle = save_stack(gfp_mask); > + > + /* Ensure page_ext is valid after page_ext_put() above */ > + page_ext = page_ext_get(page); > + if (unlikely(!page_ext)) > + return; > __set_page_owner_handle(page_ext, handle, order, gfp_mask); > + page_ext_put(); > } > > void __set_page_owner_migrate_reason(struct page *page, int reason) > { > - struct page_ext *page_ext = lookup_page_ext(page); > + struct page_ext *page_ext = page_ext_get(page); > struct page_owner *page_owner; > > if (unlikely(!page_ext)) > @@ -203,12 +211,13 @@ void __set_page_owner_migrate_reason(str > > page_owner = get_page_owner(page_ext); > page_owner->last_migrate_reason = reason; > + page_ext_put(); > } > > void __split_page_owner(struct page *page, unsigned int nr) > { > int i; > - struct page_ext *page_ext = lookup_page_ext(page); > + struct page_ext *page_ext = page_ext_get(page); > struct page_owner *page_owner; > > if (unlikely(!page_ext)) > @@ -219,16 +228,24 @@ void __split_page_owner(struct page *pag > page_owner->order = 0; > page_ext = page_ext_next(page_ext); > } > + page_ext_put(); > } > > void __folio_copy_owner(struct folio *newfolio, struct folio *old) > { > - struct page_ext *old_ext = lookup_page_ext(&old->page); > - struct page_ext *new_ext = lookup_page_ext(&newfolio->page); > + struct page_ext *old_ext; > + struct page_ext *new_ext; > struct page_owner *old_page_owner, *new_page_owner; > > - if (unlikely(!old_ext || !new_ext)) > + old_ext = page_ext_get(&old->page); > + if (unlikely(!old_ext)) > + return; > + > + new_ext = page_ext_get(&newfolio->page); > + if (unlikely(!new_ext)) { > + page_ext_put(); > return; > + } > > old_page_owner = get_page_owner(old_ext); > new_page_owner = get_page_owner(new_ext); > @@ -254,6 +271,8 @@ void __folio_copy_owner(struct folio *ne > */ > __set_bit(PAGE_EXT_OWNER, &new_ext->flags); > __set_bit(PAGE_EXT_OWNER_ALLOCATED, &new_ext->flags); > + page_ext_put(); > + page_ext_put(); > } > > void pagetypeinfo_showmixedcount_print(struct seq_file *m, > @@ -307,12 +326,12 @@ void pagetypeinfo_showmixedcount_print(s > if (PageReserved(page)) > continue; > > - page_ext = lookup_page_ext(page); > + page_ext = page_ext_get(page); > if (unlikely(!page_ext)) > continue; > > if (!test_bit(PAGE_EXT_OWNER_ALLOCATED, &page_ext->flags)) > - continue; > + goto loop; > > page_owner = get_page_owner(page_ext); > page_mt = gfp_migratetype(page_owner->gfp_mask); > @@ -323,9 +342,12 @@ void pagetypeinfo_showmixedcount_print(s > count[pageblock_mt]++; > > pfn = block_end_pfn; > + page_ext_put(); > break; > } > pfn += (1UL << page_owner->order) - 1; > +loop: > + page_ext_put(); > } > } > > @@ -435,7 +457,7 @@ err: > > void __dump_page_owner(const struct page *page) > { > - struct page_ext *page_ext = lookup_page_ext(page); > + struct page_ext *page_ext = page_ext_get((void *)page); > struct page_owner *page_owner; > depot_stack_handle_t handle; > gfp_t gfp_mask; > @@ -452,6 +474,7 @@ void __dump_page_owner(const struct page > > if (!test_bit(PAGE_EXT_OWNER, &page_ext->flags)) { > pr_alert("page_owner info is not present (never set?)\n"); > + page_ext_put(); > return; > } > > @@ -482,6 +505,7 @@ void __dump_page_owner(const struct page > if (page_owner->last_migrate_reason != -1) > pr_alert("page has been migrated, last migrate reason: %s\n", > migrate_reason_names[page_owner->last_migrate_reason]); > + page_ext_put(); > } > > static ssize_t > @@ -508,6 +532,14 @@ read_page_owner(struct file *file, char > /* Find an allocated page */ > for (; pfn < max_pfn; pfn++) { > /* > + * This temporary page_owner is required so > + * that we can avoid the context switches while holding > + * the rcu lock and copying the page owner information to > + * user through copy_to_user() or GFP_KERNEL allocations. > + */ > + struct page_owner page_owner_tmp; > + > + /* > * If the new page is in a new MAX_ORDER_NR_PAGES area, > * validate the area as existing, skip it if not > */ > @@ -525,7 +557,7 @@ read_page_owner(struct file *file, char > continue; > } > > - page_ext = lookup_page_ext(page); > + page_ext = page_ext_get(page); > if (unlikely(!page_ext)) > continue; > > @@ -534,14 +566,14 @@ read_page_owner(struct file *file, char > * because we don't hold the zone lock. > */ > if (!test_bit(PAGE_EXT_OWNER, &page_ext->flags)) > - continue; > + goto loop; > > /* > * Although we do have the info about past allocation of free > * pages, it's not relevant for current memory usage. > */ > if (!test_bit(PAGE_EXT_OWNER_ALLOCATED, &page_ext->flags)) > - continue; > + goto loop; > > page_owner = get_page_owner(page_ext); > > @@ -550,7 +582,7 @@ read_page_owner(struct file *file, char > * would inflate the stats. > */ > if (!IS_ALIGNED(pfn, 1 << page_owner->order)) > - continue; > + goto loop; > > /* > * Access to page_ext->handle isn't synchronous so we should > @@ -558,13 +590,17 @@ read_page_owner(struct file *file, char > */ > handle = READ_ONCE(page_owner->handle); > if (!handle) > - continue; > + goto loop; > > /* Record the next PFN to read in the file offset */ > *ppos = (pfn - min_low_pfn) + 1; > > + memcpy(&page_owner_tmp, page_owner, sizeof(struct page_owner)); > + page_ext_put(); > return print_page_owner(buf, count, pfn, page, > - page_owner, handle); > + &page_owner_tmp, handle); > +loop: > + page_ext_put(); > } > > return 0; > @@ -617,18 +653,20 @@ static void init_pages_in_zone(pg_data_t > if (PageReserved(page)) > continue; > > - page_ext = lookup_page_ext(page); > + page_ext = page_ext_get(page); > if (unlikely(!page_ext)) > continue; > > /* Maybe overlapping zone */ > if (test_bit(PAGE_EXT_OWNER, &page_ext->flags)) > - continue; > + goto loop; > > /* Found early allocated page */ > __set_page_owner_handle(page_ext, early_handle, > 0, 0); > count++; > +loop: > + page_ext_put(); > } > cond_resched(); > } > --- a/mm/page_table_check.c~mm-fix-use-after-free-of-page_ext-after-race-with-memory-offline > +++ a/mm/page_table_check.c > @@ -68,7 +68,7 @@ static void page_table_check_clear(struc > return; > > page = pfn_to_page(pfn); > - page_ext = lookup_page_ext(page); > + page_ext = page_ext_get(page); > anon = PageAnon(page); > > for (i = 0; i < pgcnt; i++) { > @@ -83,6 +83,7 @@ static void page_table_check_clear(struc > } > page_ext = page_ext_next(page_ext); > } > + page_ext_put(); > } > > /* > @@ -103,7 +104,7 @@ static void page_table_check_set(struct > return; > > page = pfn_to_page(pfn); > - page_ext = lookup_page_ext(page); > + page_ext = page_ext_get(page); > anon = PageAnon(page); > > for (i = 0; i < pgcnt; i++) { > @@ -118,6 +119,7 @@ static void page_table_check_set(struct > } > page_ext = page_ext_next(page_ext); > } > + page_ext_put(); > } > > /* > @@ -126,9 +128,10 @@ static void page_table_check_set(struct > */ > void __page_table_check_zero(struct page *page, unsigned int order) > { > - struct page_ext *page_ext = lookup_page_ext(page); > + struct page_ext *page_ext; > unsigned long i; > > + page_ext = page_ext_get(page); > BUG_ON(!page_ext); > for (i = 0; i < (1ul << order); i++) { > struct page_table_check *ptc = get_page_table_check(page_ext); > @@ -137,6 +140,7 @@ void __page_table_check_zero(struct page > BUG_ON(atomic_read(&ptc->file_map_count)); > page_ext = page_ext_next(page_ext); > } > + page_ext_put(); > } > > void __page_table_check_pte_clear(struct mm_struct *mm, unsigned long addr, > _ > > Patches currently in -mm which might be from quic_charante@xxxxxxxxxxx are > > mm-page_ext-remove-unused-variable-in-offline_page_ext.patch > mm-fix-use-after-free-of-page_ext-after-race-with-memory-offline.patch >
