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Wed, 29 Apr 2020 17:31:29 +0000 Received: from d06av25.portsmouth.uk.ibm.com (d06av25.portsmouth.uk.ibm.com [9.149.105.61]) by b06cxnps4076.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 03THVQMr46989428 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Wed, 29 Apr 2020 17:31:26 GMT Received: from d06av25.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 64A6E11C058; Wed, 29 Apr 2020 17:31:26 +0000 (GMT) Received: from d06av25.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 0BA0811C050; Wed, 29 Apr 2020 17:31:24 +0000 (GMT) Received: from oc7455500831.ibm.com (unknown [9.145.17.20]) by d06av25.portsmouth.uk.ibm.com (Postfix) with ESMTP; Wed, 29 Apr 2020 17:31:23 +0000 (GMT) Subject: Re: [PATCH v1 1/1] fs/splice: add missing callback for inaccessible pages To: Dave Hansen , Claudio Imbrenda , akpm@linux-foundation.org, jack@suse.cz, kirill@shutemov.name Cc: david@redhat.com, aarcange@redhat.com, linux-mm@kvack.org, frankja@linux.ibm.com, sfr@canb.auug.org.au, jhubbard@nvidia.com, linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org, peterz@infradead.org, sean.j.christopherson@intel.com References: <20200428225043.3091359-1-imbrenda@linux.ibm.com> <2a1abf38-d321-e3c7-c3b1-53b6db6da310@intel.com> From: Christian Borntraeger Autocrypt: addr=borntraeger@de.ibm.com; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: <2a1abf38-d321-e3c7-c3b1-53b6db6da310@intel.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.138,18.0.676 definitions=2020-04-29_08:2020-04-29,2020-04-29 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 bulkscore=0 phishscore=0 adultscore=0 spamscore=0 impostorscore=0 lowpriorityscore=0 malwarescore=0 mlxscore=0 mlxlogscore=999 suspectscore=0 clxscore=1015 priorityscore=1501 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2003020000 definitions=main-2004290133 Content-Transfer-Encoding: quoted-printable 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: On 29.04.20 18:07, Dave Hansen wrote: > On 4/28/20 3:50 PM, Claudio Imbrenda wrote: >> If a page is inaccesible and it is used for things like sendfile, then >> the content of the page is not always touched, and can be passed >> directly to a driver, causing issues. >> >> This patch fixes the issue by adding a call to arch_make_page_accessib= le >> in page_cache_pipe_buf_confirm; this fixes the issue. >=20 > I spent about 5 minutes putting together a patch: >=20 > https://sr71.net/~dave/intel/accessible.patch >=20 > It adds a page flag ("daccess") which starts out set. It clears the > flag it when the page is added to the page cache or mapped as anonymous= . And that of course does not work. Pages are not made unaccessible at a ra= ndom point in time. We do check for several page flags and page count before d= oing so and we also do this while with paqe_ref_freeze to avoid several races. I guess you just hit one of those.