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AJvYcCXIj/VymLbZjRU8pzxXY7+n5bECoEn1XDJoqyw1iyYK/t9D6F1VR7QQGXJQRtMGyFnChR+OHdzbmijupUk=@vger.kernel.org X-Gm-Message-State: AOJu0Yydb1FnYJdf5PAP20rLuGh9x8GYfpH/4EDWSfogM+oAqYe8jcGi rKjaKBdiMp/M6hSJ6FPc4iHLPL3DMQkUSB1eNJsYu+w22CvAAklUaHIozXJxllekIAaXd8dwEMc eReR9jw== X-Google-Smtp-Source: AGHT+IG9WPhm5XE/ZfgGaQtzh+SWoXfTwZ/PnXrEVOaIZ7eiVoVCEnZsOmLu+uDuAMPetyxG7jZDFNEKyv8= X-Received: from plai12.prod.google.com ([2002:a17:902:c94c:b0:240:2b97:90f6]) (user=surenb job=prod-delivery.src-stubby-dispatcher) by 2002:a17:903:234d:b0:23f:adc0:8cc2 with SMTP id d9443c01a7336-2422a699c3amr3040655ad.27.1753999233810; Thu, 31 Jul 2025 15:00:33 -0700 (PDT) Date: Thu, 31 Jul 2025 15:00:24 -0700 In-Reply-To: <20250731220024.702621-1-surenb@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20250731220024.702621-1-surenb@google.com> X-Mailer: git-send-email 2.50.1.565.gc32cd1483b-goog Message-ID: <20250731220024.702621-4-surenb@google.com> Subject: [PATCH 3/3] fs/proc/task_mmu: execute PROCMAP_QUERY ioctl under per-vma locks From: Suren Baghdasaryan To: akpm@linux-foundation.org Cc: Liam.Howlett@oracle.com, lorenzo.stoakes@oracle.com, david@redhat.com, vbabka@suse.cz, 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, surenb@google.com Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" 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 509fa162760a..b504b798e8fe 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 \ ) =20 -static int query_vma_setup(struct mm_struct *mm) +#ifdef CONFIG_PER_VMA_LOCK + +static int query_vma_setup(struct proc_maps_query_data *query) { - return mmap_read_lock_killable(mm); + query->locked_vma =3D NULL; + query->mmap_locked =3D false; + + return 0; } =20 -static void query_vma_teardown(struct mm_struct *mm, struct vm_area_struct= *vma) +static void query_vma_teardown(struct proc_maps_query_data *query) { - mmap_read_unlock(mm); + if (query->mmap_locked) + mmap_read_unlock(query->mm); + else + unlock_vma(query); } =20 -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_quer= y_data *query, + unsigned long addr) { - return find_vma(mm, addr); + struct vm_area_struct *vma; + struct vma_iterator vmi; + + unlock_vma(query); + rcu_read_lock(); + vma_iter_init(&vmi, query->mm, addr); + vma =3D lock_next_vma(query->mm, &vmi, addr); + rcu_read_unlock(); + + if (!IS_ERR_OR_NULL(vma)) { + query->locked_vma =3D vma; + } else if (PTR_ERR(vma) =3D=3D -EAGAIN) { + /* Fallback to mmap_lock on vma->vm_refcnt overflow */ + mmap_read_lock(query->mm); + vma =3D find_vma(query->mm, addr); + query->mmap_locked =3D true; + } + + return vma; } =20 -static struct vm_area_struct *query_matching_vma(struct mm_struct *mm, +#else /* CONFIG_PER_VMA_LOCK */ + +static int query_vma_setup(struct proc_maps_query_data *query) +{ + return mmap_read_lock_killable(query->mm); +} + +static void query_vma_teardown(struct proc_maps_query_data *query) +{ + mmap_read_unlock(query->mm); +} + +static struct vm_area_struct *query_vma_find_by_addr(struct proc_maps_quer= y_data *query, + unsigned long addr) +{ + return find_vma(query->mm, addr); +} + +#endif /* CONFIG_PER_VMA_LOCK */ + +static struct vm_area_struct *query_matching_vma(struct proc_maps_query_da= ta *query, unsigned long addr, u32 flags) { struct vm_area_struct *vma; =20 next_vma: - vma =3D query_vma_find_by_addr(mm, addr); + vma =3D query_vma_find_by_addr(query, addr); + if (IS_ERR(vma)) + return vma; + if (!vma) goto no_vma; =20 @@ -579,11 +629,11 @@ static struct vm_area_struct *query_matching_vma(stru= ct mm_struct *mm, return ERR_PTR(-ENOENT); } =20 -static int do_procmap_query(struct proc_maps_private *priv, void __user *u= arg) +static int do_procmap_query(struct mm_struct *mm, void __user *uarg) { + struct proc_maps_query_data query =3D { .mm =3D mm }; struct procmap_query karg; struct vm_area_struct *vma; - struct mm_struct *mm; const char *name =3D NULL; char build_id_buf[BUILD_ID_SIZE_MAX], *name_buf =3D NULL; __u64 usize; @@ -610,17 +660,16 @@ static int do_procmap_query(struct proc_maps_private = *priv, void __user *uarg) if (!!karg.build_id_size !=3D !!karg.build_id_addr) return -EINVAL; =20 - mm =3D priv->query.mm; if (!mm || !mmget_not_zero(mm)) return -ESRCH; =20 - err =3D query_vma_setup(mm); + err =3D query_vma_setup(&query); if (err) { mmput(mm); return err; } =20 - vma =3D query_matching_vma(mm, karg.query_addr, karg.query_flags); + vma =3D query_matching_vma(&query, karg.query_addr, karg.query_flags); if (IS_ERR(vma)) { err =3D PTR_ERR(vma); vma =3D NULL; @@ -705,7 +754,7 @@ static int do_procmap_query(struct proc_maps_private *p= riv, void __user *uarg) } =20 /* unlock vma or mmap_lock, and put mm_struct before copying data to user= */ - query_vma_teardown(mm, vma); + query_vma_teardown(&query); mmput(mm); =20 if (karg.vma_name_size && copy_to_user(u64_to_user_ptr(karg.vma_name_addr= ), @@ -725,7 +774,7 @@ static int do_procmap_query(struct proc_maps_private *p= riv, void __user *uarg) return 0; =20 out: - query_vma_teardown(mm, vma); + query_vma_teardown(&query); mmput(mm); kfree(name_buf); return err; @@ -738,7 +787,7 @@ static long procfs_procmap_ioctl(struct file *file, uns= igned int cmd, unsigned l =20 switch (cmd) { case PROCMAP_QUERY: - return do_procmap_query(priv, (void __user *)arg); + return do_procmap_query(priv->query.mm, (void __user *)arg); default: return -ENOIOCTLCMD; } --=20 2.50.1.565.gc32cd1483b-goog