From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pl1-f175.google.com (mail-pl1-f175.google.com [209.85.214.175]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 1320570827 for ; Fri, 1 Nov 2024 18:00:59 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.214.175 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1730484061; cv=none; b=hVfhC2xYK336jT7gQFEnyFxFQvkTJN+JrT9oC07xIHgQBo9Y5BL2Ru6YcYW3KZogWnacsRGjjg3x2AMvln8f8zI7HDZQjpFr+M0AxnxdmqJL/iW+Xyd2kncyD4Yl1jlKl1XOIZ5gzVEN7l+4hAkgMhZCJlH2Rd+EOmFOf0Jqfbk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1730484061; c=relaxed/simple; bh=lDxX97HRCwte7/+htCKALpm9+jdEA6tzt9fHi4sSekc=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=f/aR4DoMuFZueipP5EdaefgKTrcb/TcwYwKsRXwdL49b3htQiZIpYA2+eXusfx9gxS4VQYwwEVXdc2hwuyJMt1+w5bHrd3uKswrIMshJnvBq6lx7rSsoLAvbcp9RfXS6GE2jPNHmTfmdl8UGe2Ff2EpCxKgKBZi3qLQeIRV7PwA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=kernel.dk; spf=pass smtp.mailfrom=kernel.dk; dkim=pass (2048-bit key) header.d=kernel-dk.20230601.gappssmtp.com header.i=@kernel-dk.20230601.gappssmtp.com header.b=DszDmIyQ; arc=none smtp.client-ip=209.85.214.175 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=kernel.dk Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=kernel.dk Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel-dk.20230601.gappssmtp.com header.i=@kernel-dk.20230601.gappssmtp.com header.b="DszDmIyQ" Received: by mail-pl1-f175.google.com with SMTP id d9443c01a7336-20bb39d97d1so21180135ad.2 for ; Fri, 01 Nov 2024 11:00:59 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel-dk.20230601.gappssmtp.com; s=20230601; t=1730484059; x=1731088859; darn=vger.kernel.org; h=content-transfer-encoding:in-reply-to:from:content-language :references:cc:to:subject:user-agent:mime-version:date:message-id :from:to:cc:subject:date:message-id:reply-to; bh=ZxQwy2JqTWj9mxjVfqetkAg0pKbHnFj/zTWURSyf02U=; b=DszDmIyQVe2wigfIQbkl0Bg4gFieFC7pq+S78h2K8uSf6p7SW3bkvkCnNI4RXxZ5Nb dV2/Lu7JYKPWbVgbFE5kq9FFFlmOuudCkp4U/1Ar7QgGEQ8ojFdrahEOCiGcmx37kD1d nvAgNulv7kSV7GBhufqSmu3tlNEhjvnXvk1YvTiRliJJ5ckhtPtYWBPGrBKL2kmfWEvh 1oNcuxh1iSyWx6Yfrj5ewuzU1EsXZhUHg3t0s+TlOVOsynQ2/+6EU7gkPT4yc5yQLOYe yHGnrviCiXZpBzgThL5aHZemh/ERDs4Y9aNlOaNN5N50Sjp/DcnRgQ3P0UFSUc+2XyEO uAJA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1730484059; x=1731088859; h=content-transfer-encoding:in-reply-to:from:content-language :references:cc:to:subject:user-agent:mime-version:date:message-id :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=ZxQwy2JqTWj9mxjVfqetkAg0pKbHnFj/zTWURSyf02U=; b=geVwQMTyBtsbiu4m0CkbjlDUxaDJicCIqjHN0ESejA0FkrXJbjXFx9m6SKK/xU6R3Q szAM70nbX8afjxg/a7HF6AcIKZn0pRa7fpZHlRgMm5G1DPBkXoi+a2y0lu9q+Enl+9zo 1wVorocgXLN5kO/Vy93gDphsZhBMTUrIKlt90Cu/D5/sz2qimWSMyTpeGX9kTCl2CZ2y 5dIV+KzscG0zcXL56StXFpv2dyumMlJN10ODOsudmhunD/qsgHHqM4dPbXAv9RTdarq0 sqkb40fLRy2yGI6QSW2TZAb3lq0ga9XePYOd9ptuzJACBX0wNV+pYoFVr/NbVN1AvWFW AyAA== X-Forwarded-Encrypted: i=1; AJvYcCXe/aEk321FBsRqgKNMD19+Zs6ALfIdCgDtX1wILZm5quAK4reKP//v79+VQKAk82UKI+sKIbCY8Dz/lN0=@vger.kernel.org X-Gm-Message-State: AOJu0YwVjUL0rzpAVu4hj9SShufkZQgVYkUNTbZspFWDNGwTykTJ9F/q YNmXYZvm2S7goYlDtt11Boqqq3UudjBXZHW6SphbMyzOHgESEtb53Q5KnT3xXtic+p92N3bzKLK /Zng= X-Google-Smtp-Source: AGHT+IHIuaWcf1xcN43PpKZ8niU1vNOkNBowKv0WWyf5GdmO0yEPPdOW4bYmWtdq3vSnbd4UKzDAZg== X-Received: by 2002:a17:902:ec8c:b0:20e:5777:1b83 with SMTP id d9443c01a7336-210f75339d6mr153711675ad.24.1730484059189; Fri, 01 Nov 2024 11:00:59 -0700 (PDT) Received: from [192.168.1.150] ([198.8.77.157]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-211057a6815sm24201025ad.135.2024.11.01.11.00.57 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 01 Nov 2024 11:00:58 -0700 (PDT) Message-ID: Date: Fri, 1 Nov 2024 12:00:57 -0600 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: Eric Dumazet , Christoph Hellwig 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: Jens Axboe In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 11/1/24 11:05 AM, Eric Dumazet wrote: > > 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; Thanks Eric, I've applied your patch. -- Jens Axboe