From 6459b44b975e6e522373d831f398048a266ab6e7 Mon Sep 17 00:00:00 2001 From: Suren Baghdasaryan Date: Thu, 13 Feb 2025 14:46:53 -0800 Subject: [PATCH] mm: prepare lock_vma_under_rcu() for vma reuse possibility 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/20250213224655.1680278-17-surenb@google.com Signed-off-by: Suren Baghdasaryan Reviewed-by: Vlastimil Babka Tested-by: Shivank Garg Link: https://lkml.kernel.org/r/5e19ec93-8307-47c2-bb13-3ddf7150624e@amd.com Cc: Christian Brauner Cc: David Hildenbrand Cc: David Howells Cc: Davidlohr Bueso Cc: Hugh Dickins Cc: Jann Horn Cc: Johannes Weiner Cc: Jonathan Corbet Cc: Klara Modin Cc: Liam R. Howlett Cc: Lokesh Gidra Cc: Lorenzo Stoakes Cc: Mateusz Guzik Cc: Matthew Wilcox Cc: Mel Gorman Cc: Michal Hocko Cc: Minchan Kim Cc: Oleg Nesterov Cc: Pasha Tatashin Cc: "Paul E . McKenney" Cc: Peter Xu Cc: Peter Zijlstra (Intel) Cc: Shakeel Butt Cc: Sourav Panda Cc: Wei Yang Cc: Will Deacon Cc: Heiko Carstens Cc: Stephen Rothwell Signed-off-by: Andrew Morton --- include/linux/mm.h | 12 ++++++++---- mm/memory.c | 7 ++++--- 2 files changed, 12 insertions(+), 7 deletions(-) diff --git a/include/linux/mm.h b/include/linux/mm.h index 7377ecf5606c..f3b738562e50 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -739,10 +739,13 @@ static inline void vma_refcount_put(struct vm_area_struct *vma) * 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. * Returns the vma on success, NULL on failure to lock and EAGAIN if vma got * detached. */ -static inline struct vm_area_struct *vma_start_read(struct vm_area_struct *vma) +static inline struct vm_area_struct *vma_start_read(struct mm_struct *mm, + struct vm_area_struct *vma) { int oldcnt; @@ -753,7 +756,7 @@ static inline struct vm_area_struct *vma_start_read(struct vm_area_struct *vma) * 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 NULL; /* @@ -780,7 +783,7 @@ static inline struct vm_area_struct *vma_start_read(struct vm_area_struct *vma) * after it has been unlocked. * This pairs with RELEASE semantics in vma_end_write_all(). */ - if (unlikely(vma->vm_lock_seq == raw_read_seqcount(&vma->vm_mm->mm_lock_seq))) { + if (unlikely(vma->vm_lock_seq == raw_read_seqcount(&mm->mm_lock_seq))) { vma_refcount_put(vma); return NULL; } @@ -914,7 +917,8 @@ struct vm_area_struct *lock_vma_under_rcu(struct mm_struct *mm, #else /* CONFIG_PER_VMA_LOCK */ static inline void vma_lock_init(struct vm_area_struct *vma, bool reset_refcnt) {} -static inline struct vm_area_struct *vma_start_read(struct vm_area_struct *vma) +static inline struct vm_area_struct *vma_start_read(struct mm_struct *mm, + struct vm_area_struct *vma) { return NULL; } static inline void vma_end_read(struct vm_area_struct *vma) {} static inline void vma_start_write(struct vm_area_struct *vma) {} diff --git a/mm/memory.c b/mm/memory.c index 698b9409750f..f1d676c7ca58 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -6454,7 +6454,7 @@ retry: if (!vma) goto inval; - vma = vma_start_read(vma); + vma = vma_start_read(mm, vma); if (IS_ERR_OR_NULL(vma)) { /* Check if the VMA got isolated after we found it */ if (PTR_ERR(vma) == -EAGAIN) { @@ -6473,8 +6473,9 @@ retry: * 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(); -- 2.50.1