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AJvYcCVpjRRZr/E/yLXBWIBKmqj7Nc6udoREq9UpFbSsWSpgh/TYaa7L/H0L79N5Bx+jdSBuRPlPYewxvdAP0Ng=@vger.kernel.org X-Gm-Message-State: AOJu0YxrJDAHqa67pTBk4WECIHlT3nwsaqdhI9o1PNWgrY4Va+FSKrIM t39pgnqRCDuAoP6SJWpuj2Jhmtf/O7mWRE3pG281Srzi2JhL88dsH2bTBXfNgdxaWBwgEHNpmMY 7nQ== X-Google-Smtp-Source: AGHT+IGjcICUXwS1wYeFYZR+XrM2Xg014/1EfWbXSEfTLiETYQCBjkJqO1ncD1j5guZx5QFaNlxV4IfN5dY= X-Received: from plld7.prod.google.com ([2002:a17:902:7287:b0:223:8244:94f6]) (user=surenb job=prod-delivery.src-stubby-dispatcher) by 2002:a17:903:1744:b0:227:e980:919d with SMTP id d9443c01a7336-22c536207dfmr51660975ad.47.1744998616385; Fri, 18 Apr 2025 10:50:16 -0700 (PDT) Date: Fri, 18 Apr 2025 10:49:57 -0700 In-Reply-To: <20250418174959.1431962-1-surenb@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20250418174959.1431962-1-surenb@google.com> X-Mailer: git-send-email 2.49.0.805.g082f7c87e0-goog Message-ID: <20250418174959.1431962-7-surenb@google.com> Subject: [PATCH v3 6/8] mm: make vm_area_struct anon_name field RCU-safe 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, 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" For lockless /proc/pid/maps reading we have to ensure all the fields used when generating the output are RCU-safe. The only pointer fields in vm_area_struct which are used to generate that file's output are vm_file and anon_name. vm_file is RCU-safe but anon_name is not. Make anon_name RCU-safe as well. Signed-off-by: Suren Baghdasaryan --- include/linux/mm_inline.h | 10 +++++++++- include/linux/mm_types.h | 3 ++- mm/madvise.c | 30 ++++++++++++++++++++++++++---- 3 files changed, 37 insertions(+), 6 deletions(-) diff --git a/include/linux/mm_inline.h b/include/linux/mm_inline.h index f9157a0c42a5..9ac2d92d7ede 100644 --- a/include/linux/mm_inline.h +++ b/include/linux/mm_inline.h @@ -410,7 +410,7 @@ static inline void dup_anon_vma_name(struct vm_area_str= uct *orig_vma, struct anon_vma_name *anon_name =3D anon_vma_name(orig_vma); =20 if (anon_name) - new_vma->anon_name =3D anon_vma_name_reuse(anon_name); + rcu_assign_pointer(new_vma->anon_name, anon_vma_name_reuse(anon_name)); } =20 static inline void free_anon_vma_name(struct vm_area_struct *vma) @@ -432,6 +432,8 @@ static inline bool anon_vma_name_eq(struct anon_vma_nam= e *anon_name1, !strcmp(anon_name1->name, anon_name2->name); } =20 +struct anon_vma_name *anon_vma_name_get_rcu(struct vm_area_struct *vma); + #else /* CONFIG_ANON_VMA_NAME */ static inline void anon_vma_name_get(struct anon_vma_name *anon_name) {} static inline void anon_vma_name_put(struct anon_vma_name *anon_name) {} @@ -445,6 +447,12 @@ static inline bool anon_vma_name_eq(struct anon_vma_na= me *anon_name1, return true; } =20 +static inline +struct anon_vma_name *anon_vma_name_get_rcu(struct vm_area_struct *vma) +{ + return NULL; +} + #endif /* CONFIG_ANON_VMA_NAME */ =20 static inline void init_tlb_flush_pending(struct mm_struct *mm) diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h index 56d07edd01f9..15ec288d4a21 100644 --- a/include/linux/mm_types.h +++ b/include/linux/mm_types.h @@ -700,6 +700,7 @@ struct vm_userfaultfd_ctx {}; =20 struct anon_vma_name { struct kref kref; + struct rcu_head rcu; /* The name needs to be at the end because it is dynamically sized. */ char name[]; }; @@ -874,7 +875,7 @@ struct vm_area_struct { * terminated string containing the name given to the vma, or NULL if * unnamed. Serialized by mmap_lock. Use anon_vma_name to access. */ - struct anon_vma_name *anon_name; + struct anon_vma_name __rcu *anon_name; #endif struct vm_userfaultfd_ctx vm_userfaultfd_ctx; } __randomize_layout; diff --git a/mm/madvise.c b/mm/madvise.c index 8433ac9b27e0..ed03a5a2c140 100644 --- a/mm/madvise.c +++ b/mm/madvise.c @@ -101,14 +101,15 @@ void anon_vma_name_free(struct kref *kref) { struct anon_vma_name *anon_name =3D container_of(kref, struct anon_vma_name, kref); - kfree(anon_name); + kfree_rcu(anon_name, rcu); } =20 struct anon_vma_name *anon_vma_name(struct vm_area_struct *vma) { mmap_assert_locked(vma->vm_mm); =20 - return vma->anon_name; + return rcu_dereference_protected(vma->anon_name, + rwsem_is_locked(&vma->vm_mm->mmap_lock)); } =20 /* mmap_lock should be write-locked */ @@ -118,7 +119,7 @@ static int replace_anon_vma_name(struct vm_area_struct = *vma, struct anon_vma_name *orig_name =3D anon_vma_name(vma); =20 if (!anon_name) { - vma->anon_name =3D NULL; + rcu_assign_pointer(vma->anon_name, NULL); anon_vma_name_put(orig_name); return 0; } @@ -126,11 +127,32 @@ static int replace_anon_vma_name(struct vm_area_struc= t *vma, if (anon_vma_name_eq(orig_name, anon_name)) return 0; =20 - vma->anon_name =3D anon_vma_name_reuse(anon_name); + rcu_assign_pointer(vma->anon_name, anon_vma_name_reuse(anon_name)); anon_vma_name_put(orig_name); =20 return 0; } + +/* + * Returned anon_vma_name is stable due to elevated refcount but not guara= nteed + * to be assigned to the original VMA after the call. + */ +struct anon_vma_name *anon_vma_name_get_rcu(struct vm_area_struct *vma) +{ + struct anon_vma_name __rcu *anon_name; + + WARN_ON_ONCE(!rcu_read_lock_held()); + + anon_name =3D rcu_dereference(vma->anon_name); + if (!anon_name) + return NULL; + + if (unlikely(!kref_get_unless_zero(&anon_name->kref))) + return NULL; + + return anon_name; +} + #else /* CONFIG_ANON_VMA_NAME */ static int replace_anon_vma_name(struct vm_area_struct *vma, struct anon_vma_name *anon_name) --=20 2.49.0.805.g082f7c87e0-goog