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charset="utf-8" If a driver tries to call any of the pin_user_pages*(FOLL_LONGTERM) family of functions, and requests "too many" pages, then the call will erroneously leave pages pinned. This is visible in user space as an actual memory leak. Repro is trivial: just make enough pin_user_pages(FOLL_LONGTERM) calls to exhaust memory. The root cause of the problem is this sequence, within __gup_longterm_locked(): __get_user_pages_locked() rc =3D check_and_migrate_movable_pages() ...which gets retried in a loop. The loop error handling is incomplete, clearly due to a somewhat unusual and complicated tri-state error API. But anyway, if -ENOMEM, or in fact, any unexpected error is returned from check_and_migrate_movable_pages(), then __gup_longterm_locked() happily returns the error, while leaving the pages pinned. In the failed case, which is an app that requests (via a device driver) 30720000000 bytes to be pinned, and then exits, I see this: $ grep foll /proc/vmstat nr_foll_pin_acquired 7502048 nr_foll_pin_released 2048 And after applying this patch, it returns to balanced pins: $ grep foll /proc/vmstat nr_foll_pin_acquired 7502048 nr_foll_pin_released 7502048 Fix this by unpinning the pages that __get_user_pages_locked() has pinned, in such error cases. Fixes: 24a95998e9ba ("mm/gup.c: simplify and fix check_and_migrate_movable_= pages() return codes") Reviewed-by: Alistair Popple Acked-by: David Hildenbrand Cc: Shigeru Yoshida Cc: Jason Gunthorpe Cc: Minchan Kim Cc: Pasha Tatashin Signed-off-by: John Hubbard --- mm/gup.c | 11 +++++++++++ 1 file changed, 11 insertions(+) diff --git a/mm/gup.c b/mm/gup.c index a82890b46a36..233c284e8e66 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -2492,6 +2492,17 @@ static long __gup_longterm_locked(struct mm_struct *= mm, =20 /* FOLL_LONGTERM implies FOLL_PIN */ rc =3D check_and_migrate_movable_pages(nr_pinned_pages, pages); + + /* + * The __get_user_pages_locked() call happens before we know if + * it's possible to successfully complete the whole operation. + * To compensate for this, if we get an unexpected error (such + * as -ENOMEM) then we must unpin everything, before erroring + * out. + */ + if (rc !=3D -EAGAIN && rc !=3D 0) + unpin_user_pages(pages, nr_pinned_pages); + } while (rc =3D=3D -EAGAIN); 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charset="utf-8" If check_and_migrate_movable_pages() fails, typically with -ENOMEM, then memfd_pin_folios() will leave pages pinned. Those are leaked forever, and are visible to user space as a memory leak. Fix this by unpinning the folios that try_grab_folio(FOLL_PIN) has pinned, in such error cases. Fixes: 89c1905d9c14 ("mm/gup: introduce memfd_pin_folios() for pinning memf= d folios") Suggested-by: David Hildenbrand Cc: Alistair Popple Cc: Vivek Kasireddy Cc: Jason Gunthorpe Cc: Christoph Hellwig Cc: Dave Airlie Cc: Gerd Hoffmann Cc: Matthew Wilcox (Oracle) Cc: Daniel Vetter Cc: Hugh Dickins Cc: Peter Xu Cc: Dongwon Kim Cc: Junxiao Chang Cc: Arnd Bergmann Cc: Christoph Hellwig Cc: Mike Kravetz Cc: Oscar Salvador Signed-off-by: John Hubbard --- mm/gup.c | 8 +++----- 1 file changed, 3 insertions(+), 5 deletions(-) diff --git a/mm/gup.c b/mm/gup.c index 233c284e8e66..dc4906243b97 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -3719,12 +3719,10 @@ long memfd_pin_folios(struct file *memfd, loff_t st= art, loff_t end, ret =3D check_and_migrate_movable_folios(nr_folios, folios); } while (ret =3D=3D -EAGAIN); =20 - memalloc_pin_restore(flags); - return ret ? ret : nr_folios; err: memalloc_pin_restore(flags); - unpin_folios(folios, nr_folios); - - return ret; + if (ret) + unpin_folios(folios, nr_folios); + return ret ? ret : nr_folios; } EXPORT_SYMBOL_GPL(memfd_pin_folios); --=20 2.47.0