Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Tue, 2 May 2023 10:08:28 -0400
From:   "Liam R. Howlett" <Liam.Howlett@Oracle.com>
To:     Michael Keyes <mgkeyes@vigovproductions.net>
Cc:     Tad <support@spotco.us>, akpm@linux-foundation.org,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        rick.p.edgecombe@intel.com
Subject: Re: [PATCH v2] mm/mmap: Regression fix for unmapped_area{_topdown}
Message-ID: <20230502140828.hilf3myxj6kpiunz@revolver>
Mail-Followup-To: "Liam R. Howlett" <Liam.Howlett@Oracle.com>,
        Michael Keyes <mgkeyes@vigovproductions.net>,
        Tad <support@spotco.us>, akpm@linux-foundation.org,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        rick.p.edgecombe@intel.com
References: <e6108286ac025c268964a7ead3aab9899f9bc6e9.camel@spotco.us>
 <90777046-a420-b19f-1847-d353b9938131@vigovproductions.net>
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
Content-Transfer-Encoding: quoted-printable
In-Reply-To: <90777046-a420-b19f-1847-d353b9938131@vigovproductions.net>
User-Agent: NeoMutt/20220429
MIME-Version: 1.0
X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1
X-MS-Exchange-AntiSpam-MessageData-0: =?utf-8?B?dGFSeUNGZUhvaUlIdTZUM0dMek5xZi8yZDVRTkVUQlA3YUZzcUJzQUVyU29l?=
 =?utf-8?B?elZGSzR6N2tqc3N1LzhXb29oZ25ST0ZHdFkrM2tkeTllMzZTTGpMUFdpTlVK?=
 =?utf-8?B?Wm1hY2FvOWZ2aHZYaUJJTEVpazVnNUJGdTlMNFFBRXF0T1VSbzRJcjlld254?=
 =?utf-8?B?bHc4UnJsY3ZsZldpRWJQcy9GMGZJcndVcEsrSHkxWnRmVm9DVDFjQ1p3d1Vt?=
 =?utf-8?B?ZE03OVFyRTF2R2hXenlnc3k3RHhWNyszOVFIb2dWNkxicVhsZTFUU2dpK3h0?=
 =?utf-8?B?WWJyZURRQWxYbi9pZUhkdFd0bFZuNkkvend6N2xMLzZ2b2FFb1N2cHFrUTRS?=
 =?utf-8?B?TndzZkRnbGkzbzBDaDlsNThQTkxTaG94aEs3SkNMdnZPK0JjT3JKaEVnZEVt?=
 =?utf-8?B?bW52WmpqUnhKbzZzdjloSDRCQW85L3Y0RjRORzBvYTNsbXI4R3NwamFUUWk5?=
 =?utf-8?B?UnhLek1CRFZydFRUKzBjL3pHQ1I2NUMvenhoc0xmWDA4MG13Qk9saTk2RXE0?=
 =?utf-8?B?RFJFQng4ak83c21ZS1krTUluT2xOOVFXekcyNVVGMXZBcU1SS0V6RHNMRVdF?=
 =?utf-8?B?dkwxbFRnTEhaSU02Y0F4OWFIRk9QNEMvVHpJOWF5UnduakV4dkRqa1lQZ2c3?=
 =?utf-8?B?SEp0VzEwMVI0K0tUMHRiRnlNWGl0czZKU0wwWVVTVit0NUtkWmIzWlNTOW9W?=
 =?utf-8?B?SmdlYTZkRi9KNmEzbkxoaldRSUQydFpiZDdoc1JqQnNsdkw0ZVJUYS8xQzhw?=
 =?utf-8?B?S2N1NE5PL3FkV3JlVzFWTERud3kvRHdKYWYzQUt4ZHpJbWxHclNBM1ZCYXJS?=
 =?utf-8?B?Nkh2bHRFMVpyS2VHM1hic1Nnak1iejhUMWxXczdmc1M1NXFXRk9hMjRDMFFY?=
 =?utf-8?B?YVZUVERJUHBZSTAxVGJZV0hhWEU4cFdNajZSRmhnY0RMUW05Z1pyUlFsWWVl?=
 =?utf-8?B?NUErZ2dQWkhpRnMrR2J6ZEtGK0s0Nk5nRU1JVjN5SEJlY3I5SHhaNUJ5cHYx?=
 =?utf-8?B?L2l2T2hQNXc5VGpGdlVHU0tjaG11U3VZRFRCVXBrMjdGWjgvUmhKZVRHaStk?=
 =?utf-8?B?ZzAzUkNMbkNNTERTOVdUWW5VQkwzZ2xkS05EelQ4UFRQVVd2NEkwMTB5MzBw?=
 =?utf-8?B?aUhEOEMzTkw1R1J2VHpKeU05T1BIaHpEOUxCZkpaSzl3WG1TbFpUVUc4U3ZR?=
 =?utf-8?B?ay8vSU9hT3NGdTZNWXhYMnlYaTZ3Z3BhWGhud2NTc0JSMDRCbDhLdDZ0d3pl?=
 =?utf-8?B?TnhqeXNxbytCZnlqOW9lc2NSbWFSWEsvbnhFWWcxdEdiSHlIMUt6N0ZUNVU2?=
 =?utf-8?B?d1kyQk9EeStMWWIwZnEvbjAzZnR1cVR2U0M1ZEhMTTBRVktHZ2RjcVFkNC9P?=
 =?utf-8?B?TWg1d3Bta1l5aS9DaldIbFdRYytjWDVXblFVN1RoWkthQnFrUzYyVWp6L1du?=
 =?utf-8?B?dCtMWjlBY3J4VmFvRUhTdlV3MzQxcVpKbFJqRWdBZkZZTWVrSVNFZGt4akxq?=
 =?utf-8?B?eEdRbWhzczRQZmp5Z0xEalVGbENuOEhzZ0FGZjFFdExPSVp3WFUybnpXYkpK?=
 =?utf-8?B?UVNhc3p5Zy83NmtXQVNsUkVac1pmRVJzWnhUZmtIMmZWR2lKbFgxSG1qQUJT?=
 =?utf-8?B?SHJwdkpSam9ab3ZuM2NwbmVvdFBWQzFNT25xR2FRUUE0NnE1M014T25yQThW?=
 =?utf-8?B?Ym1TREpma01WcmVXZjdGL2dBZXlsMllyaGEwdDFLVHpqNGFVdUdndmYvVFNh?=
 =?utf-8?B?RHBnelZ3a2NDMG5QSUlKSms1b1hqQ1h0NHBnZkR3VysxNGZuMGs1c3VsN0RM?=
 =?utf-8?B?WlJ4OWx3UHg5MkZMakVVMWRSUUp2OU8zSjd1U0hZWVNhWHJjQVlzZkRzVVNH?=
 =?utf-8?B?RUZweWlWVFo3VWdIUWZKTnZXS3lueFo1dnJrdW5WN2hpOEN1TlRQOXlGdVZv?=
 =?utf-8?B?VGpoWFlHclhWTDBQL1A2cDVVbzYxSG1QYmQxb3g2S1NHdThZSmk4b2tmTGdr?=
 =?utf-8?B?VU9heFZoS2xLalh0S3J1MTAweGUzdWljWWJvMURRVkU2TXRUK1dZR0xXTEwx?=
 =?utf-8?B?RUZHTlVsTHR6dm9OWVJyVlNGOEV5aTl2WkVyVU1nOENWNHJqQWJGM3RqNUZU?=
 =?utf-8?B?a0Y1WUtFTlZ3dlZHSWFQQ1hkaFl6UmFJelJSeFZOcWc4dnRwanhlOXVNOHBY?=
 =?utf-8?B?M0E9PQ==?=
X-MS-Exchange-AntiSpam-ExternalHop-MessageData-ChunkCount: 1
X-MS-Exchange-AntiSpam-ExternalHop-MessageData-0: =?utf-8?B?NFVlTTN5Vy9Tbm45VVZZL3BGMkExN2FCSWFhazdXeHlXOEhSUDBnWEwvVkZr?=
 =?utf-8?B?Rml2NWxtU01sR1QwQ3VZOEdxdnQxKys4aUQ4elZlcFFnU3lJOWVoRC82dCtU?=
 =?utf-8?B?ZDIzeTlWT244SEc0MGVkMFFVeDJKbkI5U2hFZUR2ZjZlbjJpWE1meVlFSmpt?=
 =?utf-8?B?NTl4MWFIMi9sY2ZrUUFxR2g3R0ZJVkFRbmJPRVZCa1IzOFdFQnpOcnVEemJ4?=
 =?utf-8?B?M3pWUjBtcHN2aDZ1SmN1TldIR0JkVlZiMzBLU08zamdPNEJmVlM4SkszNTNk?=
 =?utf-8?B?SGJSaG0zVit1UjZUZHh2WENaZHJBZVZoelhkMmJ6R1RuUWdtdkZyT3RxVlNB?=
 =?utf-8?B?d1pnTSs4bVp0dUpIQU9LS0ZHallnMzlRbGlzQndmMUIvZmg0YmgwOGZ3KzZk?=
 =?utf-8?B?TVUwVW1nRFV6OENEblZITmc2eWhYa2Vrcy9Wd0hmNVRZS2IrdUc3SU9tc0Rz?=
 =?utf-8?B?cTNLY0ZkTTlYbEJacHNqTnhmdkZBU1BxeUlqOWVwMVJ2c3F2cFg0MzNycXZm?=
 =?utf-8?B?Zm9KRm5YWmU3VUVRMzAxRm5mUzEwNUZteHU3VWs0aXhHM3QrbzRYZ1QrU1Ns?=
 =?utf-8?B?UXpsRktqOGlDd01vQ2FNMEpFR0VlODJyeEcyU3g3U3oyb2dmMkl3VFF0VE0z?=
 =?utf-8?B?b3doOXBVc3doVDFLTUNodmc1WGI1WkkwTDJNMFRlNUF2dTEzbXpTVzU2d2t2?=
 =?utf-8?B?MVdyN0JHUDcyS1FCWi9lQ1gxQm1DdjlNUjJuZm00bXlXWGlnRjhqNnc4WlNa?=
 =?utf-8?B?V0FZL2ZvRkE1U1ZJUlZGcmpSdjJ5UkEwL1FrMCtHZ0tnZkVXb0UyRFNwTUJm?=
 =?utf-8?B?T1BuaFdjSDVESk9ad2E2TmdGRFErL3FScWNHR0hVK3NIT2svZ01ud1RsZ01Y?=
 =?utf-8?B?dFlTVUh0SWJHb3JVSnp4M0MzQjlSYkZHQWIvQVU5Nk9ZTzRCblpIS3ZZSlpX?=
 =?utf-8?B?c3BISStCR1AxY294Ukt3aDM1b0w0WllvUnNXM0dQYVU1ZzV0YnpiK3h6MXJX?=
 =?utf-8?B?aWZIRFdjQ2orZ0ZramFJTFI4dE00Ym1ieXovMEx4ZXZhTTJ4bGNsNjZRNTkr?=
 =?utf-8?B?SkFzOHlNSThTWGNPWDlDdEtoM01vSEZLUGwybytyeHEwR0tWaC9QZ0llOHd6?=
 =?utf-8?B?OXpnKzFtVDdtQUNDLzlXc29Rem5PblR4eGFUM2xLZ0FtR0lNM0JiOTFLb0RI?=
 =?utf-8?B?MEw0SFFnWG1LbEdDTEZLN3I3RGlYbUJYdTl1SThZWlgxZnZFNm5URTVPSDM5?=
 =?utf-8?Q?BgvRJzkJg+78OzX?=
X-OriginatorOrg: oracle.com
X-MS-Exchange-CrossTenant-Network-Message-Id: 0039368a-2c7a-4b72-a543-08db4b16b5d0
X-MS-Exchange-CrossTenant-AuthSource: SN6PR10MB3022.namprd10.prod.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 02 May 2023 14:08:31.6653
 (UTC)
X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted
X-MS-Exchange-CrossTenant-Id: 4e2c6054-71cb-48f1-bd6c-3a9705aca71b
X-MS-Exchange-CrossTenant-MailboxType: HOSTED
X-MS-Exchange-CrossTenant-UserPrincipalName: JHyBw599qzU40qiN9aK6IoCaxRDmM0L4KFWUcc6P3LpWu9vWZV6yjjZE4KOZ8kZBndzraVgu9zhPaVnAHBiUiQ==
X-MS-Exchange-Transport-CrossTenantHeadersStamped: DM6PR10MB4250
X-Proofpoint-Virus-Version: vendor=baseguard
 engine=ICAP:2.0.254,Aquarius:18.0.942,Hydra:6.0.573,FMLib:17.11.170.22
 definitions=2023-05-02_08,2023-04-27_01,2023-02-09_01
X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 adultscore=0 phishscore=0 spamscore=0
 mlxlogscore=999 bulkscore=0 suspectscore=0 mlxscore=0 malwarescore=0
 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2303200000
 definitions=main-2305020120
X-Proofpoint-GUID: rE2mKM_I1Y2-p8mGjtUrosC2X4BsJ3WQ
X-Proofpoint-ORIG-GUID: rE2mKM_I1Y2-p8mGjtUrosC2X4BsJ3WQ
X-Spam-Status: No, score=-2.8 required=5.0 tests=BAYES_00,DKIM_SIGNED,
        DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_LOW,
        RCVD_IN_MSPIKE_H2,SPF_HELO_NONE,SPF_NONE,T_SCC_BODY_TEXT_LINE
        autolearn=ham autolearn_force=no version=3.4.6
X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on
        lindbergh.monkeyblade.net
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

* Michael Keyes <mgkeyes@vigovproductions.net> [230430 18:41]:
> On 29.04.23 15:32, Tad wrote:
> > This reintroduces the issue described in
> > https://lore.kernel.org/linux-mm/cb8dc31a-fef2-1d09-f133-e9f7b9f9e77a@s=
ony.com/
> Yes, I also ran into this (even though I'd somehow missed it the
> previous time).

Rick Edgecombe reported something similar [1].

This is probably to do with my stack guard checks I recently added.

>=20
> Apparently the issue arises at mm/mmap.c:1582, where low_limit is set to
> vm_end_gap(tmp). Occasionally, this returns a 64-bit address (e.g.
> 0x7fedea581000), which is obviously greater than high_limit for a 32-bit
> mmap, and causes the next call to mas_empty_area() to fail.
>=20
> I'm not sure why vm_end_gap(tmp) occasionally returns a 64-bit address,
> or if the best solution is to just check for this and skip the retry if
> it occurs=E2=80=A6
>=20

Thanks for the debugging.  I will look into it.

I am currently trying to revise how the iterators, prev/next deal with
shifting outside the requested limits.  I suspect it's something to do
with hitting the limit and what someone would assume the next operation
means.

[1] https://lore.kernel.org/linux-mm/32f156ba80010fd97dbaf0a0cdfc8436660862=
4d.camel@intel.com/