The patch titled
Subject: mm: prepare lock_vma_under_rcu() for vma reuse possibility
has been added to the -mm mm-unstable branch. Its filename is
mm-prepare-lock_vma_under_rcu-for-vma-reuse-possibility.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-prepare-lock_vma_under_rcu-for-vma-reuse-possibility.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Suren Baghdasaryan <surenb@xxxxxxxxxx>
Subject: mm: prepare lock_vma_under_rcu() for vma reuse possibility
Date: Thu, 26 Dec 2024 09:07:07 -0800
Once we make vma cache SLAB_TYPESAFE_BY_RCU, it will be possible for a vma
to be reused and attached to another mm after lock_vma_under_rcu() locks
the vma. lock_vma_under_rcu() should ensure that vma_start_read() is using
the original mm and after locking the vma it should ensure that vma->vm_mm
has not changed from under us.
Link: https://lkml.kernel.org/r/20241226170710.1159679-16-surenb@xxxxxxxxxx
Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
Cc: Christian Brauner <brauner@xxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: David Howells <dhowells@xxxxxxxxxx>
Cc: Davidlohr Bueso <dave@xxxxxxxxxxxx>
Cc: Hillf Danton <hdanton@xxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Jann Horn <jannh@xxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Jonathan Corbet <corbet@xxxxxxx>
Cc: kernel test robot <oliver.sang@xxxxxxxxx>
Cc: Klara Modin <klarasmodin@xxxxxxxxx>
Cc: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx>
Cc: Lokesh Gidra <lokeshgidra@xxxxxxxxxx>
Cc: Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx>
Cc: Mateusz Guzik <mjguzik@xxxxxxxxx>
Cc: Matthew Wilcox (Oracle) <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 <peterz@xxxxxxxxxxxxx>
Cc: Shakeel Butt <shakeel.butt@xxxxxxxxx>
Cc: Sourav Panda <souravpanda@xxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/mm.h | 10 ++++++----
mm/memory.c | 7 ++++---
2 files changed, 10 insertions(+), 7 deletions(-)
--- a/include/linux/mm.h~mm-prepare-lock_vma_under_rcu-for-vma-reuse-possibility
+++ a/include/linux/mm.h
@@ -730,8 +730,10 @@ static inline void vma_refcount_put(stru
* Try to read-lock a vma. The function is allowed to occasionally yield false
* locked result to avoid performance overhead, in which case we fall back to
* using mmap_lock. The function should never yield false unlocked result.
+ * False locked result is possible if mm_lock_seq overflows or if vma gets
+ * reused and attached to a different mm before we lock it.
*/
-static inline bool vma_start_read(struct vm_area_struct *vma)
+static inline bool vma_start_read(struct mm_struct *mm, struct vm_area_struct *vma)
{
int oldcnt;
@@ -742,7 +744,7 @@ static inline bool vma_start_read(struct
* we don't rely on for anything - the mm_lock_seq read against which we
* need ordering is below.
*/
- if (READ_ONCE(vma->vm_lock_seq) == READ_ONCE(vma->vm_mm->mm_lock_seq.sequence))
+ if (READ_ONCE(vma->vm_lock_seq) == READ_ONCE(mm->mm_lock_seq.sequence))
return false;
@@ -767,7 +769,7 @@ static inline bool vma_start_read(struct
* This pairs with RELEASE semantics in vma_end_write_all().
*/
if (unlikely(oldcnt & VMA_LOCK_OFFSET ||
- vma->vm_lock_seq == raw_read_seqcount(&vma->vm_mm->mm_lock_seq))) {
+ vma->vm_lock_seq == raw_read_seqcount(&mm->mm_lock_seq))) {
vma_refcount_put(vma);
return false;
}
@@ -905,7 +907,7 @@ struct vm_area_struct *lock_vma_under_rc
static inline void vma_lockdep_init(struct vm_area_struct *vma) {}
static inline void vma_init_lock(struct vm_area_struct *vma, bool reset_refcnt) {}
-static inline bool vma_start_read(struct vm_area_struct *vma)
+static inline bool vma_start_read(struct mm_struct *mm, struct vm_area_struct *vma)
{ return false; }
static inline void vma_end_read(struct vm_area_struct *vma) {}
static inline void vma_start_write(struct vm_area_struct *vma) {}
--- a/mm/memory.c~mm-prepare-lock_vma_under_rcu-for-vma-reuse-possibility
+++ a/mm/memory.c
@@ -6414,7 +6414,7 @@ struct vm_area_struct *lock_vma_under_rc
if (!vma)
goto inval;
- if (!vma_start_read(vma))
+ if (!vma_start_read(mm, vma))
goto inval;
/*
@@ -6424,8 +6424,9 @@ struct vm_area_struct *lock_vma_under_rc
* fields are accessible for RCU readers.
*/
- /* Check since vm_start/vm_end might change before we lock the VMA */
- if (unlikely(address < vma->vm_start || address >= vma->vm_end))
+ /* Check if the vma we locked is the right one. */
+ if (unlikely(vma->vm_mm != mm ||
+ address < vma->vm_start || address >= vma->vm_end))
goto inval_end_read;
rcu_read_unlock();
_
Patches currently in -mm which might be from surenb@xxxxxxxxxx are
seqlock-add-raw_seqcount_try_begin.patch
mm-convert-mm_lock_seq-to-a-proper-seqcount.patch
mm-introduce-mmap_lock_speculate_try_beginretry.patch
mm-introduce-vma_start_read_locked_nested-helpers.patch
mm-move-per-vma-lock-into-vm_area_struct.patch
mm-mark-vma-as-detached-until-its-added-into-vma-tree.patch
mm-modify-vma_iter_store_gfp-to-indicate-if-its-storing-a-new-vma.patch
mm-mark-vmas-detached-upon-exit.patch
mm-nommu-fix-the-last-places-where-vma-is-not-locked-before-being-attached.patch
types-move-struct-rcuwait-into-typesh.patch
mm-allow-vma_start_read_locked-vma_start_read_locked_nested-to-fail.patch
mm-move-mmap_init_lock-out-of-the-header-file.patch
mm-uninline-the-main-body-of-vma_start_write.patch
refcount-introduce-__refcount_addinc_not_zero_limited.patch
mm-replace-vm_lock-and-detached-flag-with-a-reference-count.patch
mm-debug-print-vm_refcnt-state-when-dumping-the-vma.patch
mm-debug-print-vm_refcnt-state-when-dumping-the-vma-fix.patch
mm-remove-extra-vma_numab_state_init-call.patch
mm-prepare-lock_vma_under_rcu-for-vma-reuse-possibility.patch
mm-make-vma-cache-slab_typesafe_by_rcu.patch
docs-mm-document-latest-changes-to-vm_lock.patch
