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AJvYcCX9F9jKv0er5n9RVWZ+BqAyuIkDwIZOZYMGf+cpwQlNKxwIhWZg79bIHglcz7SWm+voaQUTCxlb3FjPz7I=@vger.kernel.org X-Gm-Message-State: AOJu0Yyj32eFf09NShjAItqsinJSz/b6wsxqZHdzqYGJBoWZHYaGyUB4 9jtS21HujVY2MvrSceJ7Tl3G9Mp4oz2TYpRkHgxG9Q9S5kvuWIdO61KGVMeHGS88UZDm2BIjrlK TlQ== X-Google-Smtp-Source: AGHT+IGF9wx4sL6ywqvbmTtYVKg94zHd41Cyf5FF+rVNBMNjdPSbsTlqGQT3TJHJNaszHYHir437UZk+8kw= X-Received: from surenb-desktop.mtv.corp.google.com ([2a00:79e0:2e3f:8:af45:bbc1:fc75:e695]) (user=surenb job=sendgmr) by 2002:a05:690c:112:b0:6ea:e559:d69c with SMTP id 00721157ae682-6eebd2afdcdmr346087b3.5.1732061319967; Tue, 19 Nov 2024 16:08:39 -0800 (PST) Date: Tue, 19 Nov 2024 16:08:25 -0800 In-Reply-To: <20241120000826.335387-1-surenb@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20241120000826.335387-1-surenb@google.com> X-Mailer: git-send-email 2.47.0.338.g60cca15819-goog Message-ID: <20241120000826.335387-5-surenb@google.com> Subject: [PATCH v4 4/5] mm: make vma cache SLAB_TYPESAFE_BY_RCU From: Suren Baghdasaryan To: akpm@linux-foundation.org Cc: willy@infradead.org, liam.howlett@oracle.com, lorenzo.stoakes@oracle.com, mhocko@suse.com, vbabka@suse.cz, hannes@cmpxchg.org, mjguzik@gmail.com, oliver.sang@intel.com, mgorman@techsingularity.net, david@redhat.com, peterx@redhat.com, oleg@redhat.com, dave@stgolabs.net, paulmck@kernel.org, brauner@kernel.org, dhowells@redhat.com, hdanton@sina.com, hughd@google.com, minchan@google.com, jannh@google.com, shakeel.butt@linux.dev, souravpanda@google.com, pasha.tatashin@soleen.com, corbet@lwn.net, linux-doc@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@android.com, surenb@google.com Content-Type: text/plain; charset="UTF-8" To enable SLAB_TYPESAFE_BY_RCU for vma cache we need to ensure that object reuse before RCU grace period is over will be detected inside lock_vma_under_rcu(). lock_vma_under_rcu() enters RCU read section, finds the vma at the given address, locks the vma and checks if it got detached or remapped to cover a different address range. These last checks are there to ensure that the vma was not modified after we found it but before locking it. vma reuse introduces several new possibilities: 1. vma can be reused after it was found but before it is locked; 2. vma can be reused and reinitialized (including changing its vm_mm) while being locked in vma_start_read(); 3. vma can be reused and reinitialized after it was found but before it is locked, then attached at a new address or to a new mm while being read-locked; For case #1 current checks will help detecting cases when: - vma was reused but not yet added into the tree (detached check) - vma was reused at a different address range (address check); We are missing the check for vm_mm to ensure the reused vma was not attached to a different mm. This patch adds the missing check. For case #2, we pass mm to vma_start_read() to prevent access to unstable vma->vm_mm. For case #3, we ensure the order in which vma->detached flag and vm_start/vm_end/vm_mm are set and checked. vma gets attached after vm_start/vm_end/vm_mm were set and lock_vma_under_rcu() should check vma->detached before checking vm_start/vm_end/vm_mm. This is required because attaching vma happens without vma write-lock, as opposed to vma detaching, which requires vma write-lock. This patch adds memory barriers inside is_vma_detached() and vma_mark_attached() needed to order reads and writes to vma->detached vs vm_start/vm_end/vm_mm. After these provisions, SLAB_TYPESAFE_BY_RCU is added to vm_area_cachep. This will facilitate vm_area_struct reuse and will minimize the number of call_rcu() calls. Adding a freeptr_t into vm_area_struct (unioned with vm_start/vm_end) could be used to avoids bloating the structure, however currently custom free pointers are not supported in combination with a ctor (see the comment for kmem_cache_args.freeptr_offset). Signed-off-by: Suren Baghdasaryan --- include/linux/mm.h | 60 +++++++++++++++++++++++++++----- include/linux/mm_types.h | 13 +++---- kernel/fork.c | 53 +++++++++++++++++----------- mm/memory.c | 15 +++++--- mm/vma.c | 2 +- tools/testing/vma/vma_internal.h | 7 ++-- 6 files changed, 103 insertions(+), 47 deletions(-) diff --git a/include/linux/mm.h b/include/linux/mm.h index dd1b6190df28..2a4794b7a513 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -257,7 +257,7 @@ struct vm_area_struct *vm_area_alloc(struct mm_struct *); struct vm_area_struct *vm_area_dup(struct vm_area_struct *); void vm_area_free(struct vm_area_struct *); /* Use only if VMA has no other users */ -void __vm_area_free(struct vm_area_struct *vma); +void vm_area_free_unreachable(struct vm_area_struct *vma); #ifndef CONFIG_MMU extern struct rb_root nommu_region_tree; @@ -690,12 +690,32 @@ static inline void vma_lock_init(struct vm_area_struct *vma) vma->vm_lock_seq = UINT_MAX; } +#define VMA_BEFORE_LOCK offsetof(struct vm_area_struct, vm_lock) +#define VMA_LOCK_END(vma) \ + (((void *)(vma)) + offsetofend(struct vm_area_struct, vm_lock)) +#define VMA_AFTER_LOCK \ + (sizeof(struct vm_area_struct) - offsetofend(struct vm_area_struct, vm_lock)) + +static inline void vma_clear(struct vm_area_struct *vma) +{ + /* Preserve vma->vm_lock */ + memset(vma, 0, VMA_BEFORE_LOCK); + memset(VMA_LOCK_END(vma), 0, VMA_AFTER_LOCK); +} + +static inline void vma_copy(struct vm_area_struct *new, struct vm_area_struct *orig) +{ + /* Preserve vma->vm_lock */ + data_race(memcpy(new, orig, VMA_BEFORE_LOCK)); + data_race(memcpy(VMA_LOCK_END(new), VMA_LOCK_END(orig), VMA_AFTER_LOCK)); +} + /* * 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. */ -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) { /* * Check before locking. A race might cause false locked result. @@ -704,7 +724,7 @@ static inline bool 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 false; if (unlikely(down_read_trylock(&vma->vm_lock.lock) == 0)) @@ -721,7 +741,7 @@ static inline bool 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))) { up_read(&vma->vm_lock.lock); return false; } @@ -810,7 +830,15 @@ static inline void vma_assert_locked(struct vm_area_struct *vma) static inline void vma_mark_attached(struct vm_area_struct *vma) { - vma->detached = false; + /* + * This pairs with smp_rmb() inside is_vma_detached(). + * vma is marked attached after all vma modifications are done and it + * got added into the vma tree. All prior vma modifications should be + * made visible before marking the vma attached. + */ + smp_wmb(); + /* This pairs with READ_ONCE() in is_vma_detached(). */ + WRITE_ONCE(vma->detached, false); } static inline void vma_mark_detached(struct vm_area_struct *vma) @@ -822,7 +850,18 @@ static inline void vma_mark_detached(struct vm_area_struct *vma) static inline bool is_vma_detached(struct vm_area_struct *vma) { - return vma->detached; + bool detached; + + /* This pairs with WRITE_ONCE() in vma_mark_attached(). */ + detached = READ_ONCE(vma->detached); + /* + * This pairs with smp_wmb() inside vma_mark_attached() to ensure + * vma->detached is read before vma attributes read later inside + * lock_vma_under_rcu(). + */ + smp_rmb(); + + return detached; } static inline void release_fault_lock(struct vm_fault *vmf) @@ -847,7 +886,11 @@ 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) {} -static inline bool vma_start_read(struct vm_area_struct *vma) +static inline void vma_clear(struct vm_area_struct *vma) + { memset(vma, 0, sizeof(*vma)); } +static inline void vma_copy(struct vm_area_struct *new, struct vm_area_struct *orig) + { data_race(memcpy(new, orig, sizeof(*new))); } +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) {} @@ -883,7 +926,7 @@ extern const struct vm_operations_struct vma_dummy_vm_ops; static inline void vma_init(struct vm_area_struct *vma, struct mm_struct *mm) { - memset(vma, 0, sizeof(*vma)); + vma_clear(vma); vma->vm_mm = mm; vma->vm_ops = &vma_dummy_vm_ops; INIT_LIST_HEAD(&vma->anon_vma_chain); @@ -892,7 +935,6 @@ static inline void vma_init(struct vm_area_struct *vma, struct mm_struct *mm) vma->detached = true; #endif vma_numab_state_init(vma); - vma_lock_init(vma); } /* Use when VMA is not part of the VMA tree and needs no locking */ diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h index 5c4bfdcfac72..8f6b0c935c2b 100644 --- a/include/linux/mm_types.h +++ b/include/linux/mm_types.h @@ -667,15 +667,10 @@ struct vma_numab_state { struct vm_area_struct { /* The first cache line has the info for VMA tree walking. */ - union { - struct { - /* VMA covers [vm_start; vm_end) addresses within mm */ - unsigned long vm_start; - unsigned long vm_end; - }; -#ifdef CONFIG_PER_VMA_LOCK - struct rcu_head vm_rcu; /* Used for deferred freeing. */ -#endif + struct { + /* VMA covers [vm_start; vm_end) addresses within mm */ + unsigned long vm_start; + unsigned long vm_end; }; /* diff --git a/kernel/fork.c b/kernel/fork.c index f0cec673583c..76c68b041f8a 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -436,6 +436,11 @@ static struct kmem_cache *vm_area_cachep; /* SLAB cache for mm_struct structures (tsk->mm) */ static struct kmem_cache *mm_cachep; +static void vm_area_ctor(void *data) +{ + vma_lock_init(data); +} + struct vm_area_struct *vm_area_alloc(struct mm_struct *mm) { struct vm_area_struct *vma; @@ -462,8 +467,7 @@ struct vm_area_struct *vm_area_dup(struct vm_area_struct *orig) * orig->shared.rb may be modified concurrently, but the clone * will be reinitialized. */ - data_race(memcpy(new, orig, sizeof(*new))); - vma_lock_init(new); + vma_copy(new, orig); INIT_LIST_HEAD(&new->anon_vma_chain); #ifdef CONFIG_PER_VMA_LOCK /* vma is not locked, can't use vma_mark_detached() */ @@ -475,32 +479,37 @@ struct vm_area_struct *vm_area_dup(struct vm_area_struct *orig) return new; } -void __vm_area_free(struct vm_area_struct *vma) +static void __vm_area_free(struct vm_area_struct *vma, bool unreachable) { +#ifdef CONFIG_PER_VMA_LOCK + /* + * With SLAB_TYPESAFE_BY_RCU, vma can be reused and we need + * vma->detached to be set before vma is returned into the cache. + * This way reused object won't be used by readers until it's + * initialized and reattached. + * If vma is unreachable, there can be no other users and we + * can set vma->detached directly with no risk of a race. + * If vma is reachable, then it should have been already detached + * under vma write-lock or it was never attached. + */ + if (unreachable) + vma->detached = true; + else + VM_BUG_ON_VMA(!is_vma_detached(vma), vma); +#endif vma_numab_state_free(vma); free_anon_vma_name(vma); kmem_cache_free(vm_area_cachep, vma); } -#ifdef CONFIG_PER_VMA_LOCK -static void vm_area_free_rcu_cb(struct rcu_head *head) +void vm_area_free(struct vm_area_struct *vma) { - struct vm_area_struct *vma = container_of(head, struct vm_area_struct, - vm_rcu); - - /* The vma should not be locked while being destroyed. */ - VM_BUG_ON_VMA(rwsem_is_locked(&vma->vm_lock.lock), vma); - __vm_area_free(vma); + __vm_area_free(vma, false); } -#endif -void vm_area_free(struct vm_area_struct *vma) +void vm_area_free_unreachable(struct vm_area_struct *vma) { -#ifdef CONFIG_PER_VMA_LOCK - call_rcu(&vma->vm_rcu, vm_area_free_rcu_cb); -#else - __vm_area_free(vma); -#endif + __vm_area_free(vma, true); } static void account_kernel_stack(struct task_struct *tsk, int account) @@ -3135,9 +3144,11 @@ void __init proc_caches_init(void) sizeof(struct fs_struct), 0, SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_ACCOUNT, NULL); - vm_area_cachep = KMEM_CACHE(vm_area_struct, - SLAB_HWCACHE_ALIGN|SLAB_NO_MERGE|SLAB_PANIC| - SLAB_ACCOUNT); + vm_area_cachep = kmem_cache_create("vm_area_struct", + sizeof(struct vm_area_struct), 0, + SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_TYPESAFE_BY_RCU| + SLAB_ACCOUNT, vm_area_ctor); + mmap_init(); nsproxy_cache_init(); } diff --git a/mm/memory.c b/mm/memory.c index d0197a0c0996..b5fbc71b46bd 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -6275,10 +6275,16 @@ struct vm_area_struct *lock_vma_under_rcu(struct mm_struct *mm, if (!vma) goto inval; - if (!vma_start_read(vma)) + if (!vma_start_read(mm, vma)) goto inval; - /* Check if the VMA got isolated after we found it */ + /* + * Check if the VMA got isolated after we found it. + * Note: vma we found could have been recycled and is being reattached. + * It's possible to attach a vma while it is read-locked, however a + * read-locked vma can't be detached (detaching requires write-locking). + * Therefore if this check passes, we have an attached and stable vma. + */ if (is_vma_detached(vma)) { vma_end_read(vma); count_vm_vma_lock_event(VMA_LOCK_MISS); @@ -6292,8 +6298,9 @@ struct vm_area_struct *lock_vma_under_rcu(struct mm_struct *mm, * 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(); diff --git a/mm/vma.c b/mm/vma.c index 73104d434567..050b83df3df2 100644 --- a/mm/vma.c +++ b/mm/vma.c @@ -382,7 +382,7 @@ void remove_vma(struct vm_area_struct *vma, bool unreachable) fput(vma->vm_file); mpol_put(vma_policy(vma)); if (unreachable) - __vm_area_free(vma); + vm_area_free_unreachable(vma); else vm_area_free(vma); } diff --git a/tools/testing/vma/vma_internal.h b/tools/testing/vma/vma_internal.h index 2fed366d20ef..fd668d6cafc0 100644 --- a/tools/testing/vma/vma_internal.h +++ b/tools/testing/vma/vma_internal.h @@ -632,14 +632,15 @@ static inline void mpol_put(struct mempolicy *) { } -static inline void __vm_area_free(struct vm_area_struct *vma) +static inline void vm_area_free(struct vm_area_struct *vma) { free(vma); } -static inline void vm_area_free(struct vm_area_struct *vma) +static inline void vm_area_free_unreachable(struct vm_area_struct *vma) { - __vm_area_free(vma); + vma->detached = true; + vm_area_free(vma); } static inline void lru_add_drain(void) -- 2.47.0.338.g60cca15819-goog