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Tue, 10 Dec 2024 12:06:26 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id DbcEJMIuWGenZQAAD6G6ig (envelope-from ); Tue, 10 Dec 2024 12:06:26 +0000 Message-ID: <9f000fbf-b5c4-41f5-8a4a-9c78b37c2ec5@suse.cz> Date: Tue, 10 Dec 2024 13:06:26 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v5 4/6] mm: make vma cache SLAB_TYPESAFE_BY_RCU Content-Language: en-US To: Suren Baghdasaryan , akpm@linux-foundation.org Cc: willy@infradead.org, liam.howlett@oracle.com, lorenzo.stoakes@oracle.com, mhocko@suse.com, 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 References: <20241206225204.4008261-1-surenb@google.com> <20241206225204.4008261-5-surenb@google.com> From: Vlastimil Babka Autocrypt: addr=vbabka@suse.cz; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: DFC481C000E X-Stat-Signature: at151irtk8rjkntsmnx8p747upy98zmy X-Rspam-User: X-HE-Tag: 1733832346-703831 X-HE-Meta: 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 dw9B9xyg I5IkbgIS8DBNuc34787ZZYe54tFsyw1lVIjkW8cNrKF67mnpFQ+iXXX7sXUzXYSYfK2OnjFRJAC/3Qwk0SiPGvo7tKC+OUFrG2h8vqiGUv7DkNQ4wDSwbwjTC7FhZ21bfbKxnRokwwtlXFCdUGOXF5ZT56q/bGSz8UKoWJXMNINRCewnTdQpNJF8RNslj7AiCccJ+e+kUEAn1amou3/JUr/EP0RygMeSboAXoWKZbBYF6+P723aVQJgZ49s9nXIlITBbjtkgvGHEO3Gdm9ItkqNwuJnOuYXUZ6P2u9w8OUc5WK5l232ac9g0t4tIHIAePaeQi8hmEGDNWfBGG6M+ntTuSbNyM3fle/wE5jQ8BINmKQhE= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 12/6/24 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. > > Signed-off-by: Suren Baghdasaryan > --- > 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; > } This could have been perhaps another preparatory patch to make this one smaller? > > +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 This isn't the ideal pattern I think, now that we have a ctor. Ideally the ctor would do all this (except setting the vm_mm), and then we need to make sure it's also done when freeing the vma, to make sure the freed object is in the same state as a new object after the constructor. On freeing, things like numab_state and anon_name could be NULL'd (by the respective destructors) only when they are non-NULL and thus freeing the objects pointed to. vm_policy and vm_file could perhaps be handled same way after some refactoring (see remove_vma()), vma_dummy_vm_ops are possibly already reset by vma_close(), etc. > +} > + > +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 */