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AJvYcCUXLyUvnh8IiRzZJ7Mww9TYXa2vbjvFl8xqvrlKorkU3ARauKdwwV7mgcs236J4HqDmEVEpzUN2zfwWdQ==@vger.kernel.org, AJvYcCVD694WSf6Kl+QOkFZ1dXv25BKCrMO50S+2DhzDIpflj0hv7vph35vfW22ClQNubBZJBprtIJxIf0gIx/EA@vger.kernel.org X-Gm-Message-State: AOJu0YyIJWgI7CUKqh273Gma4pCrvH57xKgb5Q64m6FcFnVGpJQ1Xe0F CtSUQrmmjkCHorvzhXCrhUeMD5g4euoIknW2lR76hBPi4wiOE7O/AtHxBg== X-Google-Smtp-Source: AGHT+IHZo9f36HKeHQ8nkIIaPeeueznTV0N6jhrOw14GjbzmHqPBsExDr3l3qs5vRNQhImyulbV87A== X-Received: by 2002:a05:600c:350b:b0:42c:e0da:f15c with SMTP id 5b1f17b1804b1-4319acbb947mr184117575e9.20.1730480751451; Fri, 01 Nov 2024 10:05:51 -0700 (PDT) Received: from [10.0.0.4] ([78.242.150.19]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-431bd947bf4sm101333405e9.27.2024.11.01.10.05.50 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 01 Nov 2024 10:05:50 -0700 (PDT) Message-ID: Date: Fri, 1 Nov 2024 18:05:49 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] iov_iter: don't require contiguous pages in iov_iter_extract_bvec_pages To: Christoph Hellwig , axboe@kernel.dk Cc: akpm@linux-foundation.org, viro@zeniv.linux.org.uk, dhowells@redhat.com, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, ming.lei@redhat.com References: <20241024050021.627350-1-hch@lst.de> Content-Language: en-US From: Eric Dumazet In-Reply-To: <20241024050021.627350-1-hch@lst.de> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 10/24/24 7:00 AM, Christoph Hellwig wrote: > From: Ming Lei > > The iov_iter_extract_pages interface allows to return physically > discontiguous pages, as long as all but the first and last page > in the array are page aligned and page size. Rewrite > iov_iter_extract_bvec_pages to take advantage of that instead of only > returning ranges of physically contiguous pages. > > Signed-off-by: Ming Lei > [hch: minor cleanups, new commit log] > Signed-off-by: Christoph Hellwig > --- > lib/iov_iter.c | 67 +++++++++++++++++++++++++++++++++----------------- > 1 file changed, 45 insertions(+), 22 deletions(-) > > diff --git a/lib/iov_iter.c b/lib/iov_iter.c > index 1abb32c0da50..9fc06f5fb748 100644 > --- a/lib/iov_iter.c > +++ b/lib/iov_iter.c > @@ -1677,8 +1677,8 @@ static ssize_t iov_iter_extract_xarray_pages(struct iov_iter *i, > } > > /* > - * Extract a list of contiguous pages from an ITER_BVEC iterator. This does > - * not get references on the pages, nor does it get a pin on them. > + * Extract a list of virtually contiguous pages from an ITER_BVEC iterator. > + * This does not get references on the pages, nor does it get a pin on them. > */ > static ssize_t iov_iter_extract_bvec_pages(struct iov_iter *i, > struct page ***pages, size_t maxsize, > @@ -1686,35 +1686,58 @@ static ssize_t iov_iter_extract_bvec_pages(struct iov_iter *i, > iov_iter_extraction_t extraction_flags, > size_t *offset0) > { > - struct page **p, *page; > - size_t skip = i->iov_offset, offset, size; > - int k; > + size_t skip = i->iov_offset, size = 0; > + struct bvec_iter bi; > + int k = 0; > > - for (;;) { > - if (i->nr_segs == 0) > - return 0; > - size = min(maxsize, i->bvec->bv_len - skip); > - if (size) > - break; > + if (i->nr_segs == 0) > + return 0; > + > + if (i->iov_offset == i->bvec->bv_len) { > i->iov_offset = 0; > i->nr_segs--; > i->bvec++; > skip = 0; > } > + bi.bi_size = maxsize + skip; > + bi.bi_bvec_done = skip; > + > + maxpages = want_pages_array(pages, maxsize, skip, maxpages); > + > + while (bi.bi_size && bi.bi_idx < i->nr_segs) { > + struct bio_vec bv = bvec_iter_bvec(i->bvec, bi); > + > + /* > + * The iov_iter_extract_pages interface only allows an offset > + * into the first page. Break out of the loop if we see an > + * offset into subsequent pages, the caller will have to call > + * iov_iter_extract_pages again for the reminder. > + */ > + if (k) { > + if (bv.bv_offset) > + break; > + } else { > + *offset0 = bv.bv_offset; > + } > > - skip += i->bvec->bv_offset; > - page = i->bvec->bv_page + skip / PAGE_SIZE; > - offset = skip % PAGE_SIZE; > - *offset0 = offset; > + (*pages)[k++] = bv.bv_page; > + size += bv.bv_len; > > - maxpages = want_pages_array(pages, size, offset, maxpages); > - if (!maxpages) > - return -ENOMEM; > - p = *pages; > - for (k = 0; k < maxpages; k++) > - p[k] = page + k; > + if (k >= maxpages) > + break; > + > + /* > + * We are done when the end of the bvec doesn't align to a page > + * boundary as that would create a hole in the returned space. > + * The caller will handle this with another call to > + * iov_iter_extract_pages. > + */ > + if (bv.bv_offset + bv.bv_len != PAGE_SIZE) > + break; > + > + bvec_iter_advance_single(i->bvec, &bi, bv.bv_len); > + } > > - size = min_t(size_t, size, maxpages * PAGE_SIZE - offset); > iov_iter_advance(i, size); > return size; > } This is causing major network regression in UDP sendfile, found by syzbot. I will release the syzbot report and this fix : diff --git a/lib/iov_iter.c b/lib/iov_iter.c index 65ec660c2960..e19aab1fccca 100644 --- a/lib/iov_iter.c +++ b/lib/iov_iter.c @@ -1728,6 +1728,10 @@ static ssize_t iov_iter_extract_bvec_pages(struct iov_iter *i,                 (*pages)[k++] = bv.bv_page;                 size += bv.bv_len; +               if (size > maxsize) { +                       size = maxsize; +                       break; +               }                 if (k >= maxpages)                         break;