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AJvYcCVHeVhjSJ1/LuunIwiwwJYpd6FJ1JUStb8+mnx4IP7wM7hBx1THVzwxtTuTfKFgoiYW7E2YsLEkpc8AYlw=@vger.kernel.org X-Gm-Message-State: AOJu0YyCuPWOnT3+TEgzjhzLlMOePDyfPnaVNJuId55iDiI+bZtJQVfq 5xtT6/gmoechtJFINRoYiSj9UlDEcNwwMwPc6geq99Jc86f2TSvXlPUsV81M01QBqHy3GdwHkHl VMg== X-Google-Smtp-Source: AGHT+IFV1+9gbXGa72+TRMzfljX8nTas7v1/UQOwAWuQbBD3PGKS+ix9UpG8sQoR4NwvEysafdLPdictJdI= X-Received: from pjj15.prod.google.com ([2002:a17:90b:554f:b0:2ea:448a:8cd1]) (user=surenb job=prod-delivery.src-stubby-dispatcher) by 2002:a17:90b:5686:b0:2ee:df70:1ff3 with SMTP id 98e67ed59e1d1-2f548e4d0a7mr8382370a91.0.1736389844102; Wed, 08 Jan 2025 18:30:44 -0800 (PST) Date: Wed, 8 Jan 2025 18:30:16 -0800 In-Reply-To: <20250109023025.2242447-1-surenb@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20250109023025.2242447-1-surenb@google.com> X-Mailer: git-send-email 2.47.1.613.gc27f4b7a9f-goog Message-ID: <20250109023025.2242447-8-surenb@google.com> Subject: [PATCH v8 07/16] mm: allow vma_start_read_locked/vma_start_read_locked_nested to fail From: Suren Baghdasaryan To: akpm@linux-foundation.org Cc: peterz@infradead.org, willy@infradead.org, liam.howlett@oracle.com, lorenzo.stoakes@oracle.com, mhocko@suse.com, vbabka@suse.cz, hannes@cmpxchg.org, mjguzik@gmail.com, oliver.sang@intel.com, mgorman@techsingularity.net, david@redhat.com, peterx@redhat.com, oleg@redhat.com, dave@stgolabs.net, paulmck@kernel.org, brauner@kernel.org, dhowells@redhat.com, hdanton@sina.com, hughd@google.com, lokeshgidra@google.com, minchan@google.com, jannh@google.com, shakeel.butt@linux.dev, souravpanda@google.com, pasha.tatashin@soleen.com, klarasmodin@gmail.com, richard.weiyang@gmail.com, corbet@lwn.net, linux-doc@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@android.com, surenb@google.com Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" With upcoming replacement of vm_lock with vm_refcnt, we need to handle a possibility of vma_start_read_locked/vma_start_read_locked_nested failing due to refcount overflow. Prepare for such possibility by changing these APIs and adjusting their users. Signed-off-by: Suren Baghdasaryan Acked-by: Vlastimil Babka Cc: Lokesh Gidra --- include/linux/mm.h | 6 ++++-- mm/userfaultfd.c | 18 +++++++++++++----- 2 files changed, 17 insertions(+), 7 deletions(-) diff --git a/include/linux/mm.h b/include/linux/mm.h index e0d403c1ff63..6e6edfd4f3d9 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -747,10 +747,11 @@ static inline bool vma_start_read(struct vm_area_stru= ct *vma) * not be used in such cases because it might fail due to mm_lock_seq over= flow. * This functionality is used to obtain vma read lock and drop the mmap re= ad lock. */ -static inline void vma_start_read_locked_nested(struct vm_area_struct *vma= , int subclass) +static inline bool vma_start_read_locked_nested(struct vm_area_struct *vma= , int subclass) { mmap_assert_locked(vma->vm_mm); down_read_nested(&vma->vm_lock.lock, subclass); + return true; } =20 /* @@ -759,10 +760,11 @@ static inline void vma_start_read_locked_nested(struc= t vm_area_struct *vma, int * not be used in such cases because it might fail due to mm_lock_seq over= flow. * This functionality is used to obtain vma read lock and drop the mmap re= ad lock. */ -static inline void vma_start_read_locked(struct vm_area_struct *vma) +static inline bool vma_start_read_locked(struct vm_area_struct *vma) { mmap_assert_locked(vma->vm_mm); down_read(&vma->vm_lock.lock); + return true; } =20 static inline void vma_end_read(struct vm_area_struct *vma) diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c index a03c6f1ceb9e..eb2ca37b32ee 100644 --- a/mm/userfaultfd.c +++ b/mm/userfaultfd.c @@ -85,7 +85,8 @@ static struct vm_area_struct *uffd_lock_vma(struct mm_str= uct *mm, mmap_read_lock(mm); vma =3D find_vma_and_prepare_anon(mm, address); if (!IS_ERR(vma)) - vma_start_read_locked(vma); + if (!vma_start_read_locked(vma)) + vma =3D ERR_PTR(-EAGAIN); =20 mmap_read_unlock(mm); return vma; @@ -1482,10 +1483,17 @@ static int uffd_move_lock(struct mm_struct *mm, mmap_read_lock(mm); err =3D find_vmas_mm_locked(mm, dst_start, src_start, dst_vmap, src_vmap); if (!err) { - vma_start_read_locked(*dst_vmap); - if (*dst_vmap !=3D *src_vmap) - vma_start_read_locked_nested(*src_vmap, - SINGLE_DEPTH_NESTING); + if (vma_start_read_locked(*dst_vmap)) { + if (*dst_vmap !=3D *src_vmap) { + if (!vma_start_read_locked_nested(*src_vmap, + SINGLE_DEPTH_NESTING)) { + vma_end_read(*dst_vmap); + err =3D -EAGAIN; + } + } + } else { + err =3D -EAGAIN; + } } mmap_read_unlock(mm); return err; --=20 2.47.1.613.gc27f4b7a9f-goog