On Mon, Dec 9, 2024 at 9:35 AM Klara Modin <klarasmodin@xxxxxxxxx> wrote: > > Hi, > > On 2024-12-06 23:52, Suren Baghdasaryan wrote: > > 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 > > 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. This might lead to vma_start_read() returning > > a false locked result but that's not critical if it's rare because > > it will only lead to a retry under mmap_lock. > > 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. > > This patch (85ad413389aec04cfaaba043caa8128b76c6e491 in next-20241209) > seems to cause an oops on a MIPS board of mine (Cavium Octeon III) > (abbreviated, full attached): Thanks! This is really helpful because both errors are reported on architectures which don't set CONFIG_PER_VMA_LOCK. This is a great clue. I'm investigating it and will post a fix asap. Thanks, Suren. > > CPU 2 Unable to handle kernel paging request at virtual address > 0000000000000000, epc == ffffffff813a85a0, ra == ffffffff81390438 > Oops[#1]: > CPU: 2 UID: 0 PID: 1 Comm: init Not tainted > 6.13.0-rc1-00162-g85ad413389ae #156 > Call Trace: > unlink_anon_vmas (mm/rmap.c:408) > free_pgtables (mm/memory.c:393) > vms_clear_ptes (mm/vma.c:1143) > vms_complete_munmap_vmas (include/linux/mm.h:2737 mm/vma.c:1187) > do_vmi_align_munmap (mm/vma.c:1452) > __vm_munmap (mm/vma.c:2892) > sys_munmap (mm/mmap.c:1053) > syscall_common (arch/mips/kernel/scall64-n64.S:62) > > I saw that there's already a report, but maybe another arch can be > useful for tracking this down. > > Please let me know if there's anything else you need. > > Regards, > Klara Modin > > Link: https://lore.kernel.org/all/202412082208.db1fb2c9-lkp@xxxxxxxxx > > > > > Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx> > > --- > > include/linux/mm.h | 36 +++++-- > > include/linux/mm_types.h | 10 +- > > include/linux/slab.h | 6 -- > > kernel/fork.c | 157 +++++++++++++++++++++++++------ > > mm/memory.c | 15 ++- > > mm/vma.c | 2 +- > > tools/testing/vma/vma_internal.h | 7 +- > > 7 files changed, 179 insertions(+), 54 deletions(-) > > > > diff --git a/include/linux/mm.h b/include/linux/mm.h > > index 2bf38c1e9cca..3568bcbc7c81 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; > > @@ -706,8 +706,10 @@ static inline void vma_lock_init(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. > > */ > > -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. > > @@ -716,7 +718,7 @@ 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)) > > @@ -733,7 +735,7 @@ 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; > > } > > @@ -822,7 +824,15 @@ 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) > > @@ -834,7 +844,18 @@ 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) > > @@ -859,7 +880,7 @@ 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 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) {} > > @@ -893,6 +914,7 @@ static inline void assert_fault_locked(struct vm_fault *vmf) > > > > extern const struct vm_operations_struct vma_dummy_vm_ops; > > > > +/* Use on VMAs not created using vm_area_alloc() */ > > static inline void vma_init(struct vm_area_struct *vma, struct mm_struct *mm) > > { > > memset(vma, 0, sizeof(*vma)); > > diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h > > index be3551654325..5d8779997266 100644 > > --- a/include/linux/mm_types.h > > +++ b/include/linux/mm_types.h > > @@ -543,6 +543,12 @@ static inline void *folio_get_private(struct folio *folio) > > > > typedef unsigned long vm_flags_t; > > > > +/* > > + * freeptr_t represents a SLUB freelist pointer, which might be encoded > > + * and not dereferenceable if CONFIG_SLAB_FREELIST_HARDENED is enabled. > > + */ > > +typedef struct { unsigned long v; } freeptr_t; > > + > > /* > > * A region containing a mapping of a non-memory backed file under NOMMU > > * conditions. These are held in a global tree and are pinned by the VMAs that > > @@ -657,9 +663,7 @@ struct vm_area_struct { > > unsigned long vm_start; > > unsigned long vm_end; > > }; > > -#ifdef CONFIG_PER_VMA_LOCK > > - struct rcu_head vm_rcu; /* Used for deferred freeing. */ > > -#endif > > + freeptr_t vm_freeptr; /* Pointer used by SLAB_TYPESAFE_BY_RCU */ > > }; > > > > /* > > diff --git a/include/linux/slab.h b/include/linux/slab.h > > index 10a971c2bde3..681b685b6c4e 100644 > > --- a/include/linux/slab.h > > +++ b/include/linux/slab.h > > @@ -234,12 +234,6 @@ enum _slab_flag_bits { > > #define SLAB_NO_OBJ_EXT __SLAB_FLAG_UNUSED > > #endif > > > > -/* > > - * freeptr_t represents a SLUB freelist pointer, which might be encoded > > - * and not dereferenceable if CONFIG_SLAB_FREELIST_HARDENED is enabled. > > - */ > > -typedef struct { unsigned long v; } freeptr_t; > > - > > /* > > * ZERO_SIZE_PTR will be returned for zero sized kmalloc requests. > > * > > diff --git a/kernel/fork.c b/kernel/fork.c > > index 71990f46aa4e..e7e76a660e4c 100644 > > --- a/kernel/fork.c > > +++ b/kernel/fork.c > > @@ -436,6 +436,98 @@ 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) > > +{ > > + struct vm_area_struct *vma = (struct vm_area_struct *)data; > > + > > +#ifdef CONFIG_PER_VMA_LOCK > > + /* vma is not locked, can't use vma_mark_detached() */ > > + vma->detached = true; > > +#endif > > + INIT_LIST_HEAD(&vma->anon_vma_chain); > > + vma_lock_init(vma); > > +} > > + > > +#ifdef CONFIG_PER_VMA_LOCK > > + > > +static void vma_clear(struct vm_area_struct *vma, struct mm_struct *mm) > > +{ > > + vma->vm_mm = mm; > > + vma->vm_ops = &vma_dummy_vm_ops; > > + vma->vm_start = 0; > > + vma->vm_end = 0; > > + vma->anon_vma = NULL; > > + vma->vm_pgoff = 0; > > + vma->vm_file = NULL; > > + vma->vm_private_data = NULL; > > + vm_flags_init(vma, 0); > > + memset(&vma->vm_page_prot, 0, sizeof(vma->vm_page_prot)); > > + memset(&vma->shared, 0, sizeof(vma->shared)); > > + memset(&vma->vm_userfaultfd_ctx, 0, sizeof(vma->vm_userfaultfd_ctx)); > > + vma_numab_state_init(vma); > > +#ifdef CONFIG_ANON_VMA_NAME > > + vma->anon_name = NULL; > > +#endif > > +#ifdef CONFIG_SWAP > > + memset(&vma->swap_readahead_info, 0, sizeof(vma->swap_readahead_info)); > > +#endif > > +#ifndef CONFIG_MMU > > + vma->vm_region = NULL; > > +#endif > > +#ifdef CONFIG_NUMA > > + vma->vm_policy = NULL; > > +#endif > > +} > > + > > +static void vma_copy(const struct vm_area_struct *src, struct vm_area_struct *dest) > > +{ > > + dest->vm_mm = src->vm_mm; > > + dest->vm_ops = src->vm_ops; > > + dest->vm_start = src->vm_start; > > + dest->vm_end = src->vm_end; > > + dest->anon_vma = src->anon_vma; > > + dest->vm_pgoff = src->vm_pgoff; > > + dest->vm_file = src->vm_file; > > + dest->vm_private_data = src->vm_private_data; > > + vm_flags_init(dest, src->vm_flags); > > + memcpy(&dest->vm_page_prot, &src->vm_page_prot, > > + sizeof(dest->vm_page_prot)); > > + memcpy(&dest->shared, &src->shared, sizeof(dest->shared)); > > + memcpy(&dest->vm_userfaultfd_ctx, &src->vm_userfaultfd_ctx, > > + sizeof(dest->vm_userfaultfd_ctx)); > > +#ifdef CONFIG_ANON_VMA_NAME > > + dest->anon_name = src->anon_name; > > +#endif > > +#ifdef CONFIG_SWAP > > + memcpy(&dest->swap_readahead_info, &src->swap_readahead_info, > > + sizeof(dest->swap_readahead_info)); > > +#endif > > +#ifndef CONFIG_MMU > > + dest->vm_region = src->vm_region; > > +#endif > > +#ifdef CONFIG_NUMA > > + dest->vm_policy = src->vm_policy; > > +#endif > > +} > > + > > +#else /* CONFIG_PER_VMA_LOCK */ > > + > > +static void vma_clear(struct vm_area_struct *vma, struct mm_struct *mm) > > +{ > > + vma_init(vma, mm); > > +} > > + > > +static void vma_copy(const struct vm_area_struct *src, struct vm_area_struct *dest) > > +{ > > + /* > > + * orig->shared.rb may be modified concurrently, but the clone > > + * will be reinitialized. > > + */ > > + data_race(memcpy(dest, src, sizeof(*dest))); > > +} > > + > > +#endif /* CONFIG_PER_VMA_LOCK */ > > + > > struct vm_area_struct *vm_area_alloc(struct mm_struct *mm) > > { > > struct vm_area_struct *vma; > > @@ -444,7 +536,7 @@ struct vm_area_struct *vm_area_alloc(struct mm_struct *mm) > > if (!vma) > > return NULL; > > > > - vma_init(vma, mm); > > + vma_clear(vma, mm); > > > > return vma; > > } > > @@ -458,49 +550,46 @@ struct vm_area_struct *vm_area_dup(struct vm_area_struct *orig) > > > > ASSERT_EXCLUSIVE_WRITER(orig->vm_flags); > > ASSERT_EXCLUSIVE_WRITER(orig->vm_file); > > - /* > > - * orig->shared.rb may be modified concurrently, but the clone > > - * will be reinitialized. > > - */ > > - data_race(memcpy(new, orig, sizeof(*new))); > > - vma_lock_init(new); > > - INIT_LIST_HEAD(&new->anon_vma_chain); > > -#ifdef CONFIG_PER_VMA_LOCK > > - /* vma is not locked, can't use vma_mark_detached() */ > > - new->detached = true; > > -#endif > > + vma_copy(orig, new); > > vma_numab_state_init(new); > > dup_anon_vma_name(orig, new); > > > > 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); > > + vma->vm_lock_seq = UINT_MAX; > > +#endif > > + VM_BUG_ON_VMA(!list_empty(&vma->anon_vma_chain), vma); > > 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) > > @@ -3141,6 +3230,12 @@ void __init mm_cache_init(void) > > > > void __init proc_caches_init(void) > > { > > + struct kmem_cache_args args = { > > + .use_freeptr_offset = true, > > + .freeptr_offset = offsetof(struct vm_area_struct, vm_freeptr), > > + .ctor = vm_area_ctor, > > + }; > > + > > sighand_cachep = kmem_cache_create("sighand_cache", > > sizeof(struct sighand_struct), 0, > > SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_TYPESAFE_BY_RCU| > > @@ -3157,9 +3252,11 @@ 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| > > + vm_area_cachep = kmem_cache_create("vm_area_struct", > > + sizeof(struct vm_area_struct), &args, > > + SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_TYPESAFE_BY_RCU| > > SLAB_ACCOUNT); > > + > > mmap_init(); > > nsproxy_cache_init(); > > } > > diff --git a/mm/memory.c b/mm/memory.c > > index b252f19b28c9..6f4d4d423835 100644 > > --- a/mm/memory.c > > +++ b/mm/memory.c > > @@ -6368,10 +6368,16 @@ 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); > > @@ -6385,8 +6391,9 @@ 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 cdc63728f47f..648784416833 100644 > > --- a/mm/vma.c > > +++ b/mm/vma.c > > @@ -414,7 +414,7 @@ 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 0cdc5f8c3d60..3eeb1317cc69 100644 > > --- a/tools/testing/vma/vma_internal.h > > +++ b/tools/testing/vma/vma_internal.h > > @@ -685,14 +685,15 @@ 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)
