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Thu, 28 Sep 2023 12:50:44 -0700 (PDT) MIME-Version: 1.0 References: <20230923013148.1390521-1-surenb@google.com> <20230923013148.1390521-3-surenb@google.com> In-Reply-To: From: Suren Baghdasaryan Date: Thu, 28 Sep 2023 12:50:33 -0700 Message-ID: Subject: Re: [PATCH v2 2/3] userfaultfd: UFFDIO_REMAP uABI To: Peter Xu Cc: akpm@linux-foundation.org, viro@zeniv.linux.org.uk, brauner@kernel.org, shuah@kernel.org, aarcange@redhat.com, lokeshgidra@google.com, david@redhat.com, hughd@google.com, mhocko@suse.com, axelrasmussen@google.com, rppt@kernel.org, willy@infradead.org, Liam.Howlett@oracle.com, jannh@google.com, zhangpeng362@huawei.com, bgeffon@google.com, kaleshsingh@google.com, ngeoffray@google.com, jdduke@google.com, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, kernel-team@android.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: 7338380013 X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: a8uzb34zjaayxs8rxj3b5reuggpriktt X-HE-Tag: 1695930645-503239 X-HE-Meta: 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 8rudY/Ce 4sewIv49xkbN65m7wyeuZdMLBx2XcS2zrX3HVOT2gY1QdwAhE6kgZ8SE7zHZNk7NKH9hc6K/IoY4l10G9pL8Idf+qsxhd6WqrI154kZgam0sfTsSKDzF/qQSL7fs/s++DwhTfZ2M9mo8rdDdB4CbjoLS0W5L5YM38wXn0KUOe22EyFIeZ/1G9Si7HzRHttACcvCEHzTxbzgAyZfls6DXSzpfnr2BaeS+hRkTvSeR12wawR3c+vYHVvbFDPLyu5JsHnoWB X-Bogosity: Ham, tests=bogofilter, spamicity=0.031928, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Thu, Sep 28, 2023 at 11:43=E2=80=AFAM Peter Xu wrote= : > > One more thing.. > > On Fri, Sep 22, 2023 at 06:31:45PM -0700, Suren Baghdasaryan wrote: > > +static int remap_pages_pte(struct mm_struct *dst_mm, > > [...] > > > +retry: > > + dst_pte =3D pte_offset_map_nolock(dst_mm, dst_pmd, dst_addr, &dst= _ptl); > > + > > + /* If an huge pmd materialized from under us fail */ > > + if (unlikely(!dst_pte)) { > > + err =3D -EFAULT; > > + goto out; > > + } > > + > > + src_pte =3D pte_offset_map_nolock(src_mm, src_pmd, src_addr, &src= _ptl); > > + > > + /* > > + * We held the mmap_lock for reading so MADV_DONTNEED > > + * can zap transparent huge pages under us, or the > > + * transparent huge page fault can establish new > > + * transparent huge pages under us. > > + */ > > + if (unlikely(!src_pte)) { > > + err =3D -EFAULT; > > + goto out; > > + } > > For these two places: I know that thp collapse with mmap read lock hasn't > yet spread to anon (so I assume none of above could trigger yet on the > failure paths), but shall we constantly return -EAGAIN here just in case = we > forget that in the future? > > For example, for UFFDIO_COPY over shmem which we can already hit similar > case, mfill_atomic_install_pte() has: > > ret =3D -EAGAIN; > dst_pte =3D pte_offset_map_lock(dst_mm, dst_pmd, dst_addr, &ptl); > if (!dst_pte) > goto out; > > Thanks, Retrying in this case makes sense to me. Will change. > > -- > Peter Xu > > -- > To unsubscribe from this group and stop receiving emails from it, send an= email to kernel-team+unsubscribe@android.com. >