mm/gup.c | 17 +++++++++++++++-- 1 file changed, 15 insertions(+), 2 deletions(-)
The recent addition of "pofs" (pages or folios) handling to gup has a
flaw: it assumes that unpin_user_pages() handles NULL pages in the
pages** array. That's not the case, as I discovered when I ran on a new
configuration on my test machine.
Fix this by skipping NULL pages in unpin_user_pages(), just like
unpin_folios() already does.
Details: when booting on x86 with "numa=fake=2 movablecore=4G" on Linux
6.12, and running this:
tools/testing/selftests/mm/gup_longterm
...I get the following crash:
BUG: kernel NULL pointer dereference, address: 0000000000000008
RIP: 0010:sanity_check_pinned_pages+0x3a/0x2d0
...
Call Trace:
<TASK>
? __die_body+0x66/0xb0
? page_fault_oops+0x30c/0x3b0
? do_user_addr_fault+0x6c3/0x720
? irqentry_enter+0x34/0x60
? exc_page_fault+0x68/0x100
? asm_exc_page_fault+0x22/0x30
? sanity_check_pinned_pages+0x3a/0x2d0
unpin_user_pages+0x24/0xe0
check_and_migrate_movable_pages_or_folios+0x455/0x4b0
__gup_longterm_locked+0x3bf/0x820
? mmap_read_lock_killable+0x12/0x50
? __pfx_mmap_read_lock_killable+0x10/0x10
pin_user_pages+0x66/0xa0
gup_test_ioctl+0x358/0xb20
__se_sys_ioctl+0x6b/0xc0
do_syscall_64+0x7b/0x150
entry_SYSCALL_64_after_hwframe+0x76/0x7e
Fixes: 94efde1d1539 ("mm/gup: avoid an unnecessary allocation call for FOLL_LONGTERM cases")
Cc: David Hildenbrand <david@redhat.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Vivek Kasireddy <vivek.kasireddy@intel.com>
Cc: Dave Airlie <airlied@redhat.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Dongwon Kim <dongwon.kim@intel.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Junxiao Chang <junxiao.chang@intel.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
Hi,
I got a nasty shock when I tried out a new test machine setup last
night--I wish I'd noticed the problem earlier! But anyway, this should
make it all better...
I've asked Greg K-H to hold off on including commit 94efde1d1539
("mm/gup: avoid an unnecessary allocation call for FOLL_LONGTERM cases")
in linux-stable (6.11.y), but if this fix-to-the-fix looks good, then
maybe both fixes can ultimately end up in stable.
thanks,
John Hubbard
mm/gup.c | 17 +++++++++++++++--
1 file changed, 15 insertions(+), 2 deletions(-)
diff --git a/mm/gup.c b/mm/gup.c
index ad0c8922dac3..6e417502728a 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -52,7 +52,12 @@ static inline void sanity_check_pinned_pages(struct page **pages,
*/
for (; npages; npages--, pages++) {
struct page *page = *pages;
- struct folio *folio = page_folio(page);
+ struct folio *folio;
+
+ if (!page)
+ continue;
+
+ folio = page_folio(page);
if (is_zero_page(page) ||
!folio_test_anon(folio))
@@ -248,9 +253,14 @@ static inline struct folio *gup_folio_range_next(struct page *start,
static inline struct folio *gup_folio_next(struct page **list,
unsigned long npages, unsigned long i, unsigned int *ntails)
{
- struct folio *folio = page_folio(list[i]);
+ struct folio *folio;
unsigned int nr;
+ if (!list[i])
+ return NULL;
+
+ folio = page_folio(list[i]);
+
for (nr = i + 1; nr < npages; nr++) {
if (page_folio(list[nr]) != folio)
break;
@@ -410,6 +420,9 @@ void unpin_user_pages(struct page **pages, unsigned long npages)
sanity_check_pinned_pages(pages, npages);
for (i = 0; i < npages; i += nr) {
folio = gup_folio_next(pages, npages, i, &nr);
+ if (!folio)
+ continue;
+
gup_put_folio(folio, nr, FOLL_PIN);
}
}
--
2.47.0On 19.11.24 05:49, John Hubbard wrote:
> The recent addition of "pofs" (pages or folios) handling to gup has a
> flaw: it assumes that unpin_user_pages() handles NULL pages in the
> pages** array. That's not the case, as I discovered when I ran on a new
> configuration on my test machine.
>
> Fix this by skipping NULL pages in unpin_user_pages(), just like
> unpin_folios() already does.
>
> Details: when booting on x86 with "numa=fake=2 movablecore=4G" on Linux
> 6.12, and running this:
>
> tools/testing/selftests/mm/gup_longterm
>
> ...I get the following crash:
>
> BUG: kernel NULL pointer dereference, address: 0000000000000008
> RIP: 0010:sanity_check_pinned_pages+0x3a/0x2d0
> ...
> Call Trace:
> <TASK>
> ? __die_body+0x66/0xb0
> ? page_fault_oops+0x30c/0x3b0
> ? do_user_addr_fault+0x6c3/0x720
> ? irqentry_enter+0x34/0x60
> ? exc_page_fault+0x68/0x100
> ? asm_exc_page_fault+0x22/0x30
> ? sanity_check_pinned_pages+0x3a/0x2d0
> unpin_user_pages+0x24/0xe0
> check_and_migrate_movable_pages_or_folios+0x455/0x4b0
> __gup_longterm_locked+0x3bf/0x820
> ? mmap_read_lock_killable+0x12/0x50
> ? __pfx_mmap_read_lock_killable+0x10/0x10
> pin_user_pages+0x66/0xa0
> gup_test_ioctl+0x358/0xb20
> __se_sys_ioctl+0x6b/0xc0
> do_syscall_64+0x7b/0x150
> entry_SYSCALL_64_after_hwframe+0x76/0x7e
>
> Fixes: 94efde1d1539 ("mm/gup: avoid an unnecessary allocation call for FOLL_LONGTERM cases")
> Cc: David Hildenbrand <david@redhat.com>
> Cc: Oscar Salvador <osalvador@suse.de>
> Cc: Vivek Kasireddy <vivek.kasireddy@intel.com>
> Cc: Dave Airlie <airlied@redhat.com>
> Cc: Gerd Hoffmann <kraxel@redhat.com>
> Cc: Matthew Wilcox <willy@infradead.org>
> Cc: Christoph Hellwig <hch@infradead.org>
> Cc: Jason Gunthorpe <jgg@nvidia.com>
> Cc: Peter Xu <peterx@redhat.com>
> Cc: Arnd Bergmann <arnd@arndb.de>
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> Cc: Dongwon Kim <dongwon.kim@intel.com>
> Cc: Hugh Dickins <hughd@google.com>
> Cc: Junxiao Chang <junxiao.chang@intel.com>
> Cc: <stable@vger.kernel.org>
> Signed-off-by: John Hubbard <jhubbard@nvidia.com>
> ---
>
> Hi,
>
> I got a nasty shock when I tried out a new test machine setup last
> night--I wish I'd noticed the problem earlier! But anyway, this should
> make it all better...
>
> I've asked Greg K-H to hold off on including commit 94efde1d1539
> ("mm/gup: avoid an unnecessary allocation call for FOLL_LONGTERM cases")
> in linux-stable (6.11.y), but if this fix-to-the-fix looks good, then
> maybe both fixes can ultimately end up in stable.
>
Ouch!
> thanks,
> John Hubbard
>
> mm/gup.c | 17 +++++++++++++++--
> 1 file changed, 15 insertions(+), 2 deletions(-)
>
> diff --git a/mm/gup.c b/mm/gup.c
> index ad0c8922dac3..6e417502728a 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -52,7 +52,12 @@ static inline void sanity_check_pinned_pages(struct page **pages,
> */
> for (; npages; npages--, pages++) {
> struct page *page = *pages;
> - struct folio *folio = page_folio(page);
> + struct folio *folio;
> +
> + if (!page)
> + continue;
> +
> + folio = page_folio(page);
>
> if (is_zero_page(page) ||
> !folio_test_anon(folio))
> @@ -248,9 +253,14 @@ static inline struct folio *gup_folio_range_next(struct page *start,
> static inline struct folio *gup_folio_next(struct page **list,
> unsigned long npages, unsigned long i, unsigned int *ntails)
> {
> - struct folio *folio = page_folio(list[i]);
> + struct folio *folio;
> unsigned int nr;
>
> + if (!list[i])
> + return NULL;
> +
I don't particularly enjoy returning NULL here, if we don't teach the
other users of that function about that possibility. There are two other
users.
Also: we are not setting "ntails" to 1. I think the callers uses that as
"nr" to advance npages. So the caller has to make sure to set "nr = 1"
in case it sees "NULL".
Alternatively ...
> + folio = page_folio(list[i]);
> +
> for (nr = i + 1; nr < npages; nr++) {
> if (page_folio(list[nr]) != folio)
> break;
> @@ -410,6 +420,9 @@ void unpin_user_pages(struct page **pages, unsigned long npages)
> sanity_check_pinned_pages(pages, npages);
> for (i = 0; i < npages; i += nr) {
... handle it here
if (!pages[i]) {
nr = 1;
continue;
}
No strong opinion. But I think we should either update all callers to
deal with returning NULL from this function, and set "nr = 1".
--
Cheers,
David / dhildenb
On 11/19/24 6:33 AM, David Hildenbrand wrote:
> On 19.11.24 05:49, John Hubbard wrote:
>> The recent addition of "pofs" (pages or folios) handling to gup has a
>> flaw: it assumes that unpin_user_pages() handles NULL pages in the
>> pages** array. That's not the case, as I discovered when I ran on a new
>> configuration on my test machine.
>>
>> Fix this by skipping NULL pages in unpin_user_pages(), just like
>> unpin_folios() already does.
>>
>> Details: when booting on x86 with "numa=fake=2 movablecore=4G" on Linux
>> 6.12, and running this:
>>
>> tools/testing/selftests/mm/gup_longterm
>>
>> ...I get the following crash:
>>
>> BUG: kernel NULL pointer dereference, address: 0000000000000008
>> RIP: 0010:sanity_check_pinned_pages+0x3a/0x2d0
>> ...
>> Call Trace:
>> <TASK>
>> ? __die_body+0x66/0xb0
>> ? page_fault_oops+0x30c/0x3b0
>> ? do_user_addr_fault+0x6c3/0x720
>> ? irqentry_enter+0x34/0x60
>> ? exc_page_fault+0x68/0x100
>> ? asm_exc_page_fault+0x22/0x30
>> ? sanity_check_pinned_pages+0x3a/0x2d0
>> unpin_user_pages+0x24/0xe0
>> check_and_migrate_movable_pages_or_folios+0x455/0x4b0
>> __gup_longterm_locked+0x3bf/0x820
>> ? mmap_read_lock_killable+0x12/0x50
>> ? __pfx_mmap_read_lock_killable+0x10/0x10
>> pin_user_pages+0x66/0xa0
>> gup_test_ioctl+0x358/0xb20
>> __se_sys_ioctl+0x6b/0xc0
>> do_syscall_64+0x7b/0x150
>> entry_SYSCALL_64_after_hwframe+0x76/0x7e
>>
>> Fixes: 94efde1d1539 ("mm/gup: avoid an unnecessary allocation call for FOLL_LONGTERM cases")
>> Cc: David Hildenbrand <david@redhat.com>
>> Cc: Oscar Salvador <osalvador@suse.de>
>> Cc: Vivek Kasireddy <vivek.kasireddy@intel.com>
>> Cc: Dave Airlie <airlied@redhat.com>
>> Cc: Gerd Hoffmann <kraxel@redhat.com>
>> Cc: Matthew Wilcox <willy@infradead.org>
>> Cc: Christoph Hellwig <hch@infradead.org>
>> Cc: Jason Gunthorpe <jgg@nvidia.com>
>> Cc: Peter Xu <peterx@redhat.com>
>> Cc: Arnd Bergmann <arnd@arndb.de>
>> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
>> Cc: Dongwon Kim <dongwon.kim@intel.com>
>> Cc: Hugh Dickins <hughd@google.com>
>> Cc: Junxiao Chang <junxiao.chang@intel.com>
>> Cc: <stable@vger.kernel.org>
>> Signed-off-by: John Hubbard <jhubbard@nvidia.com>
>> ---
>>
>> Hi,
>>
>> I got a nasty shock when I tried out a new test machine setup last
>> night--I wish I'd noticed the problem earlier! But anyway, this should
>> make it all better...
>>
>> I've asked Greg K-H to hold off on including commit 94efde1d1539
>> ("mm/gup: avoid an unnecessary allocation call for FOLL_LONGTERM cases")
>> in linux-stable (6.11.y), but if this fix-to-the-fix looks good, then
>> maybe both fixes can ultimately end up in stable.
>>
>
> Ouch!
>
>> thanks,
>> John Hubbard
>>
>> mm/gup.c | 17 +++++++++++++++--
>> 1 file changed, 15 insertions(+), 2 deletions(-)
>>
>> diff --git a/mm/gup.c b/mm/gup.c
>> index ad0c8922dac3..6e417502728a 100644
>> --- a/mm/gup.c
>> +++ b/mm/gup.c
>> @@ -52,7 +52,12 @@ static inline void sanity_check_pinned_pages(struct page **pages,
>> */
>> for (; npages; npages--, pages++) {
>> struct page *page = *pages;
>> - struct folio *folio = page_folio(page);
>> + struct folio *folio;
>> +
>> + if (!page)
>> + continue;
>> +
>> + folio = page_folio(page);
>> if (is_zero_page(page) ||
>> !folio_test_anon(folio))
>> @@ -248,9 +253,14 @@ static inline struct folio *gup_folio_range_next(struct page *start,
>> static inline struct folio *gup_folio_next(struct page **list,
>> unsigned long npages, unsigned long i, unsigned int *ntails)
>> {
>> - struct folio *folio = page_folio(list[i]);
>> + struct folio *folio;
>> unsigned int nr;
>> + if (!list[i])
>> + return NULL;
>> +
>
> I don't particularly enjoy returning NULL here, if we don't teach the other users of that function about that possibility. There are two other users.
>
> Also: we are not setting "ntails" to 1. I think the callers uses that as "nr" to advance npages. So the caller has to make sure to set "nr = 1" in case it sees "NULL".
>
> Alternatively ...
>
>> + folio = page_folio(list[i]);
>> +
>> for (nr = i + 1; nr < npages; nr++) {
>> if (page_folio(list[nr]) != folio)
>> break;
>> @@ -410,6 +420,9 @@ void unpin_user_pages(struct page **pages, unsigned long npages)
>> sanity_check_pinned_pages(pages, npages);
>> for (i = 0; i < npages; i += nr) {
>
> ... handle it here
>
> if (!pages[i]) {
> nr = 1;
> continue;
> }
>
> No strong opinion. But I think we should either update all callers to deal with returning NULL from this function, and set "nr = 1".
>
Yes, that makes sense. I'll send a v2 shortly with one or the other
approach implemented. I appreciate the review feedback as always!
thanks,
--
John Hubbard
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