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AJvYcCVA3pzQ5HSbsIQ84wVkllNeRc9IQrciTaJ3DYNAOeJ/FDQh0+5/eQQMT+j3GVRFuRGOrgRQCgozMA==@kvack.org X-Gm-Message-State: AOJu0YxSa3ntlGGOm5jvs7nkwp5GDWp3Nsc0qjvEgIi8U1HQhOsmeUXa vnG8xvGU6+AcfaPxmnYdYjJm747HPXTiEw43/pNqYpArPnw90HBIekUg8d4XwgcQ26LS/0PtReu QUnM+p2R/8xnxwIW7AXZDlEo40gEd27zWLC9Q X-Gm-Gg: ASbGnctE09KUbC1pb9WlTmbSZrIayB5ZpEKWK0hc2v7eg1eJyOolR2W2w/mEYucPUG6 pKUjczcSbfWcCtsxJQMgIIAPbqSiCCptJt13lSotZ9sOg3pNyeYuUgRqo8nuKb/qr5+39 X-Google-Smtp-Source: AGHT+IHYK9UpwLg8g9p8WZ/+G+K2SlEb174x5VoCFiOsuQulmL6Q/tmn9ENXIRvGtPuqmCx6/lhi7nRXXekengkGOqg= X-Received: by 2002:a05:622a:552:b0:462:b2f5:b24c with SMTP id d75a77b69052e-46b3c82797dmr3672571cf.29.1736271096520; Tue, 07 Jan 2025 09:31:36 -0800 (PST) MIME-Version: 1.0 References: <20241226170710.1159679-1-surenb@google.com> <20241226170710.1159679-9-surenb@google.com> <929630d5-3a11-47f3-ac4d-4f162a11bbdc@suse.cz> In-Reply-To: <929630d5-3a11-47f3-ac4d-4f162a11bbdc@suse.cz> From: Suren Baghdasaryan Date: Tue, 7 Jan 2025 09:31:25 -0800 X-Gm-Features: AbW1kva3MR6uMiHmqOyu_HM-hFWVk-j1pZV9D6ZKWExGeVH4miRxOoAW-P1GQcY Message-ID: Subject: Re: [PATCH v7 08/17] mm: allow vma_start_read_locked/vma_start_read_locked_nested to fail To: Vlastimil Babka Cc: akpm@linux-foundation.org, peterz@infradead.org, willy@infradead.org, liam.howlett@oracle.com, lorenzo.stoakes@oracle.com, mhocko@suse.com, 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, corbet@lwn.net, linux-doc@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@android.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Stat-Signature: jk986jmeb5rzqwbfi1ahbo341erpak5z X-Rspam-User: X-Rspamd-Queue-Id: D44692000B X-Rspamd-Server: rspam08 X-HE-Tag: 1736271097-111318 X-HE-Meta: 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 0YsgoBO1 cnr18tmcMNNnDNWbEZgghOxIipMmtOdi5xNW+KShnRVKCCm18tqSJzj6cn1YpJtf1R7MM4VJDxtDWUSTCuZUL6coRe33ILcGRVcWYHaqZ5Xsk5Cbn+gpTz2tkl3jZEUR/fR+3xmyiw8Gddskzk9dYN2K0UM0QZqG/RO7YTY6OkOtkz4y9nHzdzv8/5ISRgRjWqqWtAHgi17VyU3eCTBv6p7uHec41BY3PJse9cCJPWGvQByP8OByiF2t/4dUS04cTAD+EqHjwVsBX0H9MO+kmiyUDyfexajOC4UzCmbJhPOy1d9s= 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, Jan 7, 2025 at 9:28=E2=80=AFAM Vlastimil Babka wro= te: > > On 12/26/24 18:07, Suren Baghdasaryan wrote: > > 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 faili= ng > > due to refcount overflow. Prepare for such possibility by changing thes= e > > APIs and adjusting their users. > > > > Signed-off-by: Suren Baghdasaryan > > Cc: Lokesh Gidra > > Acked-by: Vlastimil Babka > > (I don't know if this can break some uffd users?) I checked with Lokesh who added that uffd code and he confirmed that uffd will handle errors correctly. > > > @@ -1483,10 +1484,16 @@ 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, s= rc_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_vm= ap, > > + SINGLE_DEPTH_NEST= ING)) { > > + vma_end_read(*dst_vmap); > > + err =3D -EAGAIN; > > + } > > + } > > + } else > > + err =3D -EAGAIN; > > Nit: { } per style Ack. > > > } > > mmap_read_unlock(mm); > > return err; >