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[35.185.214.157]) by smtp.gmail.com with ESMTPSA id c5-20020a056a00248500b004f6b5ddcc65sm20916192pfv.199.2022.03.29.11.45.20 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 29 Mar 2022 11:45:20 -0700 (PDT) Date: Tue, 29 Mar 2022 18:45:16 +0000 From: Sean Christopherson To: Chao Peng Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-api@vger.kernel.org, qemu-devel@nongnu.org, Paolo Bonzini , Jonathan Corbet , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , Thomas Gleixner , Ingo Molnar , Borislav Petkov , x86@kernel.org, "H . Peter Anvin" , Hugh Dickins , Jeff Layton , "J . Bruce Fields" , Andrew Morton , Mike Rapoport , Steven Price , "Maciej S . Szmigiero" , Vlastimil Babka , Vishal Annapurve , Yu Zhang , "Kirill A . Shutemov" , luto@kernel.org, jun.nakajima@intel.com, dave.hansen@intel.com, ak@linux.intel.com, david@redhat.com Subject: Re: [PATCH v5 02/13] mm: Introduce memfile_notifier Message-ID: References: <20220310140911.50924-1-chao.p.peng@linux.intel.com> <20220310140911.50924-3-chao.p.peng@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220310140911.50924-3-chao.p.peng@linux.intel.com> X-Stat-Signature: k6m58rjfbj9d1mdycrbgbb64docac9n5 Authentication-Results: imf29.hostedemail.com; dkim=pass header.d=google.com header.s=20210112 header.b=dwjAFyr7; spf=pass (imf29.hostedemail.com: domain of seanjc@google.com designates 209.85.214.179 as permitted sender) smtp.mailfrom=seanjc@google.com; dmarc=pass (policy=reject) header.from=google.com X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 7C9C712001C X-HE-Tag: 1648579522-403233 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: On Thu, Mar 10, 2022, Chao Peng wrote: > diff --git a/mm/Makefile b/mm/Makefile > index 70d4309c9ce3..f628256dce0d 100644 > +void memfile_notifier_invalidate(struct memfile_notifier_list *list, > + pgoff_t start, pgoff_t end) > +{ > + struct memfile_notifier *notifier; > + int id; > + > + id = srcu_read_lock(&srcu); > + list_for_each_entry_srcu(notifier, &list->head, list, > + srcu_read_lock_held(&srcu)) { > + if (notifier->ops && notifier->ops->invalidate) Any reason notifier->ops isn't mandatory? > + notifier->ops->invalidate(notifier, start, end); > + } > + srcu_read_unlock(&srcu, id); > +} > + > +void memfile_notifier_fallocate(struct memfile_notifier_list *list, > + pgoff_t start, pgoff_t end) > +{ > + struct memfile_notifier *notifier; > + int id; > + > + id = srcu_read_lock(&srcu); > + list_for_each_entry_srcu(notifier, &list->head, list, > + srcu_read_lock_held(&srcu)) { > + if (notifier->ops && notifier->ops->fallocate) > + notifier->ops->fallocate(notifier, start, end); > + } > + srcu_read_unlock(&srcu, id); > +} > + > +void memfile_register_backing_store(struct memfile_backing_store *bs) > +{ > + BUG_ON(!bs || !bs->get_notifier_list); > + > + list_add_tail(&bs->list, &backing_store_list); > +} > + > +void memfile_unregister_backing_store(struct memfile_backing_store *bs) > +{ > + list_del(&bs->list); Allowing unregistration of a backing store is broken. Using the _safe() variant is not sufficient to guard against concurrent modification. I don't see any reason to support this out of the gate, the only reason to support unregistering a backing store is if the backing store is implemented as a module, and AFAIK none of the backing stores we plan on supporting initially support being built as a module. These aren't exported, so it's not like that's even possible. Registration would also be broken if modules are allowed, I'm pretty sure module init doesn't run under a global lock. We can always add this complexity if it's needed in the future, but for now the easiest thing would be to tag memfile_register_backing_store() with __init and make backing_store_list __ro_after_init. > +} > + > +static int memfile_get_notifier_info(struct inode *inode, > + struct memfile_notifier_list **list, > + struct memfile_pfn_ops **ops) > +{ > + struct memfile_backing_store *bs, *iter; > + struct memfile_notifier_list *tmp; > + > + list_for_each_entry_safe(bs, iter, &backing_store_list, list) { > + tmp = bs->get_notifier_list(inode); > + if (tmp) { > + *list = tmp; > + if (ops) > + *ops = &bs->pfn_ops; > + return 0; > + } > + } > + return -EOPNOTSUPP; > +} > + > +int memfile_register_notifier(struct inode *inode, Taking an inode is a bit odd from a user perspective. Any reason not to take a "struct file *" and get the inode here? That would give callers a hint that they need to hold a reference to the file for the lifetime of the registration. > + struct memfile_notifier *notifier, > + struct memfile_pfn_ops **pfn_ops) > +{ > + struct memfile_notifier_list *list; > + int ret; > + > + if (!inode || !notifier | !pfn_ops) Bitwise | instead of logical ||. But IMO taking in a pfn_ops pointer is silly. More below. > + return -EINVAL; > + > + ret = memfile_get_notifier_info(inode, &list, pfn_ops); > + if (ret) > + return ret; > + > + spin_lock(&list->lock); > + list_add_rcu(¬ifier->list, &list->head); > + spin_unlock(&list->lock); > + > + return 0; > +} > +EXPORT_SYMBOL_GPL(memfile_register_notifier); > + > +void memfile_unregister_notifier(struct inode *inode, > + struct memfile_notifier *notifier) > +{ > + struct memfile_notifier_list *list; > + > + if (!inode || !notifier) > + return; > + > + BUG_ON(memfile_get_notifier_info(inode, &list, NULL)); Eww. Rather than force the caller to provide the inode/file and the notifier, what about grabbing the backing store itself in the notifier? struct memfile_notifier { struct list_head list; struct memfile_notifier_ops *ops; struct memfile_backing_store *bs; }; That also helps avoid confusing between "ops" and "pfn_ops". IMO, exposing memfile_backing_store to the caller isn't a big deal, and is preferable to having to rewalk multiple lists just to delete a notifier. Then this can become: void memfile_unregister_notifier(struct memfile_notifier *notifier) { spin_lock(¬ifier->bs->list->lock); list_del_rcu(¬ifier->list); spin_unlock(¬ifier->bs->list->lock); synchronize_srcu(&srcu); } and registration can be: int memfile_register_notifier(const struct file *file, struct memfile_notifier *notifier) { struct memfile_notifier_list *list; struct memfile_backing_store *bs; int ret; if (!file || !notifier) return -EINVAL; list_for_each_entry(bs, &backing_store_list, list) { list = bs->get_notifier_list(file_inode(file)); if (list) { notifier->bs = bs; spin_lock(&list->lock); list_add_rcu(¬ifier->list, &list->head); spin_unlock(&list->lock); return 0; } } return -EOPNOTSUPP; }