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AJvYcCWpv9EtKEVYUlFRhbP89AkwLCU3NLKGoJKqJ88gaNjovVMjG+LmF/yNnqfGo7bKXJ6q3QNDsE5Bdg==@kvack.org X-Gm-Message-State: AOJu0Yw0Th3GflmhdI1q268YiiygSEpg+vGE7eaVqR6vnkiHlIjTHFZh CiEoA1OQoErimLTYV+ZyKMMRcfEO6jWjq3uNIbp9wdtgpc5KKClx3BnzR3LTvMGmRIQXzh72ELD ckwVw8hVhQ3rTI0iyG1zZAAUPgdtozACvzPxtkV3X X-Gm-Gg: ASbGnctDZY70QsGI7SVOGXNwzf0gS8a/m0Sb69JXPM+Hd/pSYbqAiaBr1z7J6oInjVO VymiW92Qc09uyIiCLwP5h79ucRaLmj/x7z17JmTDP6H9z2mZN57UpJckFqKI9I9DSnUXkgz0m9c tYs702nJn50p4nEBbEfgTDemDu+CKWvANDvRGpgPesjBJy86C7yhG0N11OBy5fp4cGnApBa8jxz 28OmL2471rIHz4Y6kzTnk1n3eVztCn7RNG/oA== X-Google-Smtp-Source: AGHT+IGNgBN87aq4QIxEol6Iry1WpPeZs6N2msqSePTFM5jWMKBB+kelQvyXcVEXcEbW86sUjLIcplgHgUotOVKwENk= X-Received: by 2002:ac8:5e4b:0:b0:48a:ba32:370 with SMTP id d75a77b69052e-4b084f396fbmr3912431cf.10.1754404685401; Tue, 05 Aug 2025 07:38:05 -0700 (PDT) MIME-Version: 1.0 References: <20250804231552.1217132-1-surenb@google.com> <20250804231552.1217132-4-surenb@google.com> In-Reply-To: From: Suren Baghdasaryan Date: Tue, 5 Aug 2025 07:37:53 -0700 X-Gm-Features: Ac12FXw4MVzzUn2oCKvSzz_8aCVi1Bw7CmRaPzcL7KBJ8BbbbzRtIwg97emJVWA Message-ID: Subject: Re: [PATCH v2 3/3] fs/proc/task_mmu: execute PROCMAP_QUERY ioctl under per-vma locks To: Vlastimil Babka Cc: akpm@linux-foundation.org, 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 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 0AA2DC0019 X-Stat-Signature: d1ry47m1s9yuwtoodj3bo8iimp959aux X-Rspam-User: X-HE-Tag: 1754404686-151775 X-HE-Meta: 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 pJ/TQPlq Mq85jlT7k5xYi1t6YuKA1A0r68DT5eI3/tIwSfPTcPqSoMtsj8OoNal1XXEkgWP+u8xCegtPWSKKaiD+iLHgNMJm8SQDVLr881ihYC94/wudcSHPTY51i8QPI+94TJwi1TN7J22n4poxV8Jl4i2bBAgDQZrjleQkC+ilLdZek+VdGiyD9RMzsyiP1Ps26NZE1YSA4Gc1bi/C5ydw0j3qfhAMWtS1EzKAgPkZpLYjhOXsUylnDNurAkmh+uJMM3J7Ji2f6qWvQzTCM20MxnMLW1/H3NY8VVR1QoBWyNVrmJmaKfSM= 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 Tue, Aug 5, 2025 at 7:18=E2=80=AFAM Vlastimil Babka wro= te: > > 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, str= uct 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 =3D NULL; > > + lock_ctx->mmap_locked =3D false; > > + > > + return 0; > > } > > > > -static void query_vma_teardown(struct mm_struct *mm, struct vm_area_st= ruct *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? Ah, you are quite right. I should handle mmap_locked differently in query_vma_find_by_addr(). I will post the fix shortly. > > > + unlock_vma(lock_ctx); > > + rcu_read_lock(); > > + vma_iter_init(&vmi, lock_ctx->mm, addr); > > + vma =3D lock_next_vma(lock_ctx->mm, &vmi, addr); > > + rcu_read_unlock(); > > + > > + if (!IS_ERR_OR_NULL(vma)) { > > + lock_ctx->locked_vma =3D vma; > > + } else if (PTR_ERR(vma) =3D=3D -EAGAIN) { > > + /* Fallback to mmap_lock on vma->vm_refcnt overflow */ > > + mmap_read_lock(lock_ctx->mm); > > + vma =3D find_vma(lock_ctx->mm, addr); > > + lock_ctx->mmap_locked =3D true; > > + } > > + > > + return vma; > > } > >