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Tue, 5 Aug 2025 14:18:49 +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 ysP5MMkSkmh2LwAAD6G6ig (envelope-from ); Tue, 05 Aug 2025 14:18:49 +0000 Message-ID: Date: Tue, 5 Aug 2025 16:20:47 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 3/3] fs/proc/task_mmu: execute PROCMAP_QUERY ioctl under per-vma locks To: Suren Baghdasaryan , akpm@linux-foundation.org Cc: Liam.Howlett@oracle.com, lorenzo.stoakes@oracle.com, david@redhat.com, peterx@redhat.com, jannh@google.com, hannes@cmpxchg.org, mhocko@kernel.org, paulmck@kernel.org, shuah@kernel.org, adobriyan@gmail.com, brauner@kernel.org, josef@toxicpanda.com, yebin10@huawei.com, linux@weissschuh.net, willy@infradead.org, osalvador@suse.de, andrii@kernel.org, ryan.roberts@arm.com, christophe.leroy@csgroup.eu, tjmercier@google.com, kaleshsingh@google.com, aha310510@gmail.com, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org References: <20250804231552.1217132-1-surenb@google.com> <20250804231552.1217132-4-surenb@google.com> From: Vlastimil Babka Content-Language: en-US In-Reply-To: <20250804231552.1217132-4-surenb@google.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: C8041C0008 X-Stat-Signature: aeudzogshkz8duq5jbhodq8x7b7rgqt7 X-Rspam-User: X-Rspamd-Server: rspam11 X-HE-Tag: 1754403532-926486 X-HE-Meta: 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 G7nxasac /yxw1o9IZ5kOTvmhy2CW/Pc98lAh8Fnfwk66qwdY/83W+sRwGXqss92mGzhNe2mNso8IPsXNMbxVwIZIM85K9U8z1iBMztSe3tzCN6Op0egNF2PXnU0tkFOxc9FdbdeGh9tvy9WC307cb/oUVKPqm9EwXEo+1bSgn9xNq27rgjdYthELoDEIVpcinvRWKWVEBUxB0FwDDSG/oqGF3CK94GxScVV3Py52k2mk3sK5PtHXwynsB+LrhIMHOqICV7Y2jw/300LTWT4IWlfvvlkYm8x+cMRvnAFTojcnIJExRM5BqSIDM6kqcpBx0NjP7xKwVHOfJ9nmeesEHVpzUuKkEaArCtyOYH9FoHHY3domM+KcV35pXfmZBzIoXefbDXOATP46W1VNsHdSmMao= 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 8/5/25 1:15 AM, Suren Baghdasaryan wrote: > Utilize per-vma locks to stabilize vma after lookup without taking > mmap_lock during PROCMAP_QUERY ioctl execution. If vma lock is > contended, we fall back to mmap_lock but take it only momentarily > to lock the vma and release the mmap_lock. In a very unlikely case > of vm_refcnt overflow, this fall back path will fail and ioctl is > done under mmap_lock protection. > > This change is designed to reduce mmap_lock contention and prevent > PROCMAP_QUERY ioctl calls from blocking address space updates. > > Signed-off-by: Suren Baghdasaryan > --- > fs/proc/task_mmu.c | 81 +++++++++++++++++++++++++++++++++++++--------- > 1 file changed, 65 insertions(+), 16 deletions(-) > > diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c > index 843577aa7a32..1d06ecdbef6f 100644 > --- a/fs/proc/task_mmu.c > +++ b/fs/proc/task_mmu.c > @@ -517,28 +517,78 @@ static int pid_maps_open(struct inode *inode, struct file *file) > PROCMAP_QUERY_VMA_FLAGS \ > ) > > -static int query_vma_setup(struct mm_struct *mm) > +#ifdef CONFIG_PER_VMA_LOCK > + > +static int query_vma_setup(struct proc_maps_locking_ctx *lock_ctx) > { > - return mmap_read_lock_killable(mm); > + lock_ctx->locked_vma = NULL; > + lock_ctx->mmap_locked = false; > + > + return 0; > } > > -static void query_vma_teardown(struct mm_struct *mm, struct vm_area_struct *vma) > +static void query_vma_teardown(struct proc_maps_locking_ctx *lock_ctx) > { > - mmap_read_unlock(mm); > + if (lock_ctx->mmap_locked) > + mmap_read_unlock(lock_ctx->mm); > + else > + unlock_vma(lock_ctx); > } > > -static struct vm_area_struct *query_vma_find_by_addr(struct mm_struct *mm, unsigned long addr) > +static struct vm_area_struct *query_vma_find_by_addr(struct proc_maps_locking_ctx *lock_ctx, > + unsigned long addr) > { > - return find_vma(mm, addr); > + struct vm_area_struct *vma; > + struct vma_iterator vmi; > Hm I think we can reach here with lock_ctx->mmap_locked being true via "goto next_vma" in query_matching_vma(). In that case we should just "return find_vma()" and doing the below is wrong, no? > + unlock_vma(lock_ctx); > + rcu_read_lock(); > + vma_iter_init(&vmi, lock_ctx->mm, addr); > + vma = lock_next_vma(lock_ctx->mm, &vmi, addr); > + rcu_read_unlock(); > + > + if (!IS_ERR_OR_NULL(vma)) { > + lock_ctx->locked_vma = vma; > + } else if (PTR_ERR(vma) == -EAGAIN) { > + /* Fallback to mmap_lock on vma->vm_refcnt overflow */ > + mmap_read_lock(lock_ctx->mm); > + vma = find_vma(lock_ctx->mm, addr); > + lock_ctx->mmap_locked = true; > + } > + > + return vma; > } >