On 01.10.23 18:00, Lorenzo Stoakes wrote:
There really should be no circumstances under which a non-FOLL_NOWAIT GUP
operation fails to return any pages, so make this an error.
To catch the trivial case, simply exit early if nr_pages == 0.
This brings __get_user_pages_locked() in line with the behaviour of its
nommu variant.
Signed-off-by: Lorenzo Stoakes <lstoakes@xxxxxxxxx>
---
mm/gup.c | 11 +++++++++++
1 file changed, 11 insertions(+)
diff --git a/mm/gup.c b/mm/gup.c
index b21b33d1787e..fb2218d74ca5 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1471,6 +1471,9 @@ static __always_inline long __get_user_pages_locked(struct mm_struct *mm,
long ret, pages_done;
bool must_unlock = false;
+ if (!nr_pages)
+ return 0;
+
Probably unlikely() is reasonable. I even wonder if WARN_ON_ONCE() would
be appropriate, but likely there are weird callers that end up calling
this with nr_pages==0 ... probably they should be identified and
changed. Future work.
/*
* The internal caller expects GUP to manage the lock internally and the
* lock must be released when this returns.
@@ -1595,6 +1598,14 @@ static __always_inline long __get_user_pages_locked(struct mm_struct *mm,
mmap_read_unlock(mm);
*locked = 0;
}
+
+ /*
+ * Failing to pin anything implies something has gone wrong except when
+ * FOLL_NOWAIT is specified, so explicitly make this an error.
+ */
+ if (pages_done == 0 && !(flags & FOLL_NOWAIT))
+ return -EFAULT;
+
But who would be affected by that and why do we care about adding this
check?
This smells like a "if (WARN_ON_ONCE())", correct?
--
Cheers,
David / dhildenb
