The quilt patch titled
Subject: mm: allow vma_start_read_locked/vma_start_read_locked_nested to fail
has been removed from the -mm tree. Its filename was
mm-allow-vma_start_read_locked-vma_start_read_locked_nested-to-fail.patch
This patch was dropped because it was merged into the mm-stable branch
of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
------------------------------------------------------
From: Suren Baghdasaryan <surenb@xxxxxxxxxx>
Subject: mm: allow vma_start_read_locked/vma_start_read_locked_nested to fail
Date: Thu, 13 Feb 2025 14:46:44 -0800
With upcoming replacement of vm_lock with vm_refcnt, we need to handle a
possibility of vma_start_read_locked/vma_start_read_locked_nested failing
due to refcount overflow. Prepare for such possibility by changing these
APIs and adjusting their users.
Link: https://lkml.kernel.org/r/20250213224655.1680278-8-surenb@xxxxxxxxxx
Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
Cc: Lokesh Gidra <lokeshgidra@xxxxxxxxxx>
Tested-by: Shivank Garg <shivankg@xxxxxxx>
Link: https://lkml.kernel.org/r/5e19ec93-8307-47c2-bb13-3ddf7150624e@xxxxxxx
Reviewed-by: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Christian Brauner <brauner@xxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: David Howells <dhowells@xxxxxxxxxx>
Cc: Davidlohr Bueso <dave@xxxxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Jann Horn <jannh@xxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Jonathan Corbet <corbet@xxxxxxx>
Cc: Klara Modin <klarasmodin@xxxxxxxxx>
Cc: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx>
Cc: Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx>
Cc: Mateusz Guzik <mjguzik@xxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Pasha Tatashin <pasha.tatashin@xxxxxxxxxx>
Cc: "Paul E . McKenney" <paulmck@xxxxxxxxxx>
Cc: Peter Xu <peterx@xxxxxxxxxx>
Cc: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: Shakeel Butt <shakeel.butt@xxxxxxxxx>
Cc: Sourav Panda <souravpanda@xxxxxxxxxx>
Cc: Wei Yang <richard.weiyang@xxxxxxxxx>
Cc: Will Deacon <will@xxxxxxxxxx>
Cc: Heiko Carstens <hca@xxxxxxxxxxxxx>
Cc: Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/mm.h | 6 ++++--
mm/userfaultfd.c | 30 +++++++++++++++++++++++-------
2 files changed, 27 insertions(+), 9 deletions(-)
--- a/include/linux/mm.h~mm-allow-vma_start_read_locked-vma_start_read_locked_nested-to-fail
+++ a/include/linux/mm.h
@@ -747,10 +747,11 @@ static inline bool vma_start_read(struct
* not be used in such cases because it might fail due to mm_lock_seq overflow.
* This functionality is used to obtain vma read lock and drop the mmap read lock.
*/
-static inline void vma_start_read_locked_nested(struct vm_area_struct *vma, int subclass)
+static inline bool vma_start_read_locked_nested(struct vm_area_struct *vma, int subclass)
{
mmap_assert_locked(vma->vm_mm);
down_read_nested(&vma->vm_lock.lock, subclass);
+ return true;
}
/*
@@ -759,10 +760,11 @@ static inline void vma_start_read_locked
* not be used in such cases because it might fail due to mm_lock_seq overflow.
* This functionality is used to obtain vma read lock and drop the mmap read lock.
*/
-static inline void vma_start_read_locked(struct vm_area_struct *vma)
+static inline bool vma_start_read_locked(struct vm_area_struct *vma)
{
mmap_assert_locked(vma->vm_mm);
down_read(&vma->vm_lock.lock);
+ return true;
}
static inline void vma_end_read(struct vm_area_struct *vma)
--- a/mm/userfaultfd.c~mm-allow-vma_start_read_locked-vma_start_read_locked_nested-to-fail
+++ a/mm/userfaultfd.c
@@ -85,8 +85,12 @@ static struct vm_area_struct *uffd_lock_
mmap_read_lock(mm);
vma = find_vma_and_prepare_anon(mm, address);
- if (!IS_ERR(vma))
- vma_start_read_locked(vma);
+ if (!IS_ERR(vma)) {
+ bool locked = vma_start_read_locked(vma);
+
+ if (!locked)
+ vma = ERR_PTR(-EAGAIN);
+ }
mmap_read_unlock(mm);
return vma;
@@ -1555,12 +1559,24 @@ static int uffd_move_lock(struct mm_stru
mmap_read_lock(mm);
err = find_vmas_mm_locked(mm, dst_start, src_start, dst_vmap, src_vmap);
- if (!err) {
- vma_start_read_locked(*dst_vmap);
- if (*dst_vmap != *src_vmap)
- vma_start_read_locked_nested(*src_vmap,
- SINGLE_DEPTH_NESTING);
+ if (err)
+ goto out;
+
+ if (!vma_start_read_locked(*dst_vmap)) {
+ err = -EAGAIN;
+ goto out;
}
+
+ /* Nothing further to do if both vmas are locked. */
+ if (*dst_vmap == *src_vmap)
+ goto out;
+
+ if (!vma_start_read_locked_nested(*src_vmap, SINGLE_DEPTH_NESTING)) {
+ /* Undo dst_vmap locking if src_vmap failed to lock */
+ vma_end_read(*dst_vmap);
+ err = -EAGAIN;
+ }
+out:
mmap_read_unlock(mm);
return err;
}
_
Patches currently in -mm which might be from surenb@xxxxxxxxxx are
