Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::3:7 as permitted sender) client-ip=2620:137:e000::3:7;
Message-ID: <48c5e937-f9c2-327d-c823-a91826ed146f@oracle.com>
Date:   Thu, 21 Sep 2023 20:00:14 -0500
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101
 Thunderbird/102.10.0
Subject: Re: [PATCH] kexec: change locking mechanism to a mutex
Content-Language: en-US
To:     Andrew Morton <akpm@linux-foundation.org>
Cc:     linux-kernel@vger.kernel.org, bhe@redhat.com, vgoyal@redhat.com,
        dyoung@redhat.com, ebiederm@xmission.com,
        kexec@lists.infradead.org, sourabhjain@linux.ibm.com,
        konrad.wilk@oracle.com, boris.ostrovsky@oracle.com
References: <20230921215938.2192-1-eric.devolder@oracle.com>
 <20230921172243.d86a649d7afc835ff2caac26@linux-foundation.org>
From:   Eric DeVolder <eric.devolder@oracle.com>
In-Reply-To: <20230921172243.d86a649d7afc835ff2caac26@linux-foundation.org>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
MIME-Version: 1.0
X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1
X-MS-Exchange-AntiSpam-MessageData-0: =?utf-8?B?NkJ2b05CMFlJV3k4Uzl0U21TOWZOQ040cXNXQlVOTWhJbFVDT3RRVWVnbHFw?=
 =?utf-8?B?c09hQjVobmdNQUtlaHB3R2JLeGs0QmVzKzlBeWtFVHIrWjU2ZEtOWHB5UDR1?=
 =?utf-8?B?Ry9tRGQzYUl2ejliNXAzWCs0VGMxTFdta281VHBZdnVjYVdRWVd2WnBQYnpV?=
 =?utf-8?B?WFFscmwzOUNBTE9QNWRHdTU4MG0relQ5MGpLNmwyRk45dWpNaWNvSkN5Q1A0?=
 =?utf-8?B?dU1KODcwYlRDQjU2ZW9lOUhWeFdGRWtqQlZBS0ZGckdzQW5DZ1hPUlFyZVpk?=
 =?utf-8?B?ODV5TlIvakdDQ0RXQkd1Uk9zQlRLZFFsS25IQ3BVWjBkSVpOZTFlTkhZMXBh?=
 =?utf-8?B?UVN3UFdjYThQL3c5K2IydzRlcEQ1MURzVlpwd3NXWU5WRXNibVBCZzNhTGdk?=
 =?utf-8?B?Q1Z5UTh0RmQyOWtDM3pOb3d2L0NvWE9ncXJqSzdyU0poZmdKdG5MMUVDSFBJ?=
 =?utf-8?B?aWVxL3pabWNPU0Q3NkVQQkNGbXltbjNqRHF0SjNUQzFCWDN2dHlvcDJ1engy?=
 =?utf-8?B?MTdKK3FXcjZsUHY0UFVDd0lyNjBQclhOYkhBbm5hRDh3ZjhxY2VHNW5rQUEz?=
 =?utf-8?B?THlJanZwRDFEZXp0alJ2UW9XSXVRWmZFR1RQV0ZBcXhPZ1VaU3dzcnJXWGZq?=
 =?utf-8?B?WHdDVTJMZjZmTEsrUVRnYzUxSS91R01kdnNyOTM0am14MUFTcnNZUUtHTG5P?=
 =?utf-8?B?WUp4WHpoVFhDQTJEdXZWYnhiSVUyKzdWKzRLMzc5SmVKYllPSzFmZVprZTg5?=
 =?utf-8?B?VWNjRlZFdnZLbDZFUDdCTGRhdWhKTEVmV0pPOXhQc2hCbURnMUw3SW9lRlRB?=
 =?utf-8?B?bEhPWTBGdDV3R1ArOHFlTVM3UnZoclBxMzZLdlUxOWRuS1dDRlJQVTlTZm1k?=
 =?utf-8?B?QVlXSXRWRjRWV0VOVXpWVWszU3I5RHhvMnBKN3p0STkyM3VzdE8vTEJDbWhU?=
 =?utf-8?B?SU5Da0pFcEg5SXJlOE9JdmV0UGF2MzQySEphSDFXY29YNTF0VWd5b2puMURD?=
 =?utf-8?B?YzJST3ZDWjN2MWhFdzBFdElHclhKQ1pmZ2tHSEJmRHZSbGxkdXNsaGJVWEdm?=
 =?utf-8?B?QzF3MWI2cjFVbHdZenNVL0NndnIrc2oxUlZ3VWN5MTMzeFJ4T0JRaVdYUnlu?=
 =?utf-8?B?TzNYU1lLOXFWZ1I2bTZGQzVMVVNCdUpFelB6V0Q4b2FITXJsTjBXNjYybWM2?=
 =?utf-8?B?V1VHSjgyV3BKWjF4M0pGRUpuNVBvZ0ZRK21NM2xreVJjbC9vUm5MR0dGN2VE?=
 =?utf-8?B?WUhGcFVheFJOUGZOdnE0aUpyVXRaMEtIbnJ6QzBzenVRN2dTemZ5SmxOZzI0?=
 =?utf-8?B?SFh3TGZaTGZydVMvOTdzN1RIcGVrUHZ0VEl3VU1HUVA1eDA3UzZhK1BQb3Ax?=
 =?utf-8?B?R3ljdGxOT2JzYlRGOWxQWENPMnNTMDdxd3NMaExaUmthaFcrUnB0SFhXNWwv?=
 =?utf-8?B?Y3ZESTlObW5nL0cxanpJdEgwZjFSeG9teGZDSmNWSW9TK0d0RTUvZ1lEdWh6?=
 =?utf-8?B?QkVJQldNb2hNb1ZmckFyN3VDRFV3blhrUVZUaTlOeXMzQ283dnBWOGlaVDJV?=
 =?utf-8?B?WDE0TzBpaUNZTnZZbHk5STNuNnB5R1p3TkYrNEJOZlpqM2lOd1NxN2wvMmdJ?=
 =?utf-8?B?QWNPY3pJcDI3RUxRR3YyYzdYbEpFUWl5YUZrOVh2OU1uNlN3NmpmRHBYcWFt?=
 =?utf-8?B?cnRzaTJhcitSUGxKKzZnamNsRjRxeDZNUHFZSXZkdUI3aDkxbW5Ha2xWNmJS?=
 =?utf-8?B?aUREcjhHTXl2UGxLMThXbnc0ams3RUVVeWlmVW8yc2hHeU1FbnhIRWVieERn?=
 =?utf-8?B?SHNhOUhZMWlUMyttWHJEV3cwN3RFV3pQcng4eGFTdUI1R2RSY3ovR1JlSkg3?=
 =?utf-8?B?VnRKMVd0SHhQeXNYWlliRy9SMVMyNjhxZXBUaDVHdXJYd09UdTF1dVB5TlFB?=
 =?utf-8?B?ZnV4OGdaaUFjbFEvRXV6eVd1bVdubk5mbm1sYzE5TzF1aHFkNmF1cjhRTmRB?=
 =?utf-8?B?bEY3Nmw2bXBxMlZ6MmRJTTgwTHJheEpiRithUVRnc1BHbnFPaEpTbmJtdEtS?=
 =?utf-8?B?ZTg5eVQ3NlRvNlZaeWVoRzJ0YS9EYW9ycDhYSHBwS3J0VGpkWUZMODVMTE1z?=
 =?utf-8?B?VzV1YUlXSjcreThwMTFya1R6WjBjT0V4L0JFSncxb3B0UVRNckJBaFlnRzl2?=
 =?utf-8?B?OWc9PQ==?=
X-MS-Exchange-AntiSpam-ExternalHop-MessageData-ChunkCount: 1
X-MS-Exchange-AntiSpam-ExternalHop-MessageData-0: =?utf-8?B?SnM2QnRRZTI2M0NlNkkwKzRHdytPK0ttZ0UrWVNiUDI1MDN6bE1xQzliSE9C?=
 =?utf-8?B?dTJLQyswY1VsL3NZcm5QQVo1SElIMlQyaWs4UUVpWFV3Y3Zkb0RUbUhxUXpY?=
 =?utf-8?B?aVJpQlJyYUQ2MUdBakRsYlUrRHJUTHp2ZDlhL1VrdHJjMzRqdEZQNGZ2OGNw?=
 =?utf-8?B?K2lzZTVsa1l3SU9WakErOWRQdUFiTVM3YmtINlhMWitEU0xpKzMzV21yV0ZQ?=
 =?utf-8?B?VU44U0ZmNTBHbGg5RmJROStLWUYyVm4zRHFyMWxrN0VVS2hvenE0NXRJTUNs?=
 =?utf-8?B?eDgxd3N1TlRISFFCaHBEM1UvYTM5eWxtY0Rya25nY1lCUmR2RE9iOWIzdlVX?=
 =?utf-8?B?TytOVHdxY0taRFdXSFJNSnBscmF1TlF0WWF5UGZVSk42bk8vamtNbEZmVWdQ?=
 =?utf-8?B?VjZ4VjVPa0FhSXBaZHRhVlJMamU3N3dkUzdZVGQyV0Y2QkNrdjNNOHlCS3JB?=
 =?utf-8?B?QVRDMGFQV1kwYnlac2haRHZSNXpLbjJLVXlNLzhKZUdLdjJraDA0cHc1NFl4?=
 =?utf-8?B?RUYrQzFUcDltSXZXdUdUeGlQeHVCTTBuUFJlcUVzUVV6TTNXQnp5YmN1bTUy?=
 =?utf-8?B?S1prVXFGa0pEOFBsbGZLUmo0aEpJWk9GM08wdXc5b0lDQ3FMWjdKakM2T1Vs?=
 =?utf-8?B?QUJhVm1neCtwME9HK3U0RzMvVHJ2VnliYWxJOXFFTlhhb0wvNlhISkFpTzlv?=
 =?utf-8?B?YUcybmxyTTl6eWdxb3MzQldaWWNIRVZlUjNUV25xRXpBYTRjYVMzYzZhaWFW?=
 =?utf-8?B?L3o4ZE96clUvaHlXeGtyeEd1S1RQaFIzeUloWFFqSmR6L1o4MWVqRlZESUtP?=
 =?utf-8?B?SlBoUldMRHlKQWNOb2QrU1dJYkJXYmcvcVlrbnd2QUFxZFQ5dzFRZzhqMEVp?=
 =?utf-8?B?SW9BeTZTQkw5SWpLSmp2V0JOYVpjc2VuREdidnBxTk9GZGZnclhjL1J5WVJi?=
 =?utf-8?B?amxDUUw4UkRoVm1pR1JRcVJUZWZac3FwV1h3S0hLSVlNSVQyb2Z1UFUvKzNr?=
 =?utf-8?B?MEpoaHNDV2ZLN2gvY1ZENGtUeFE3ZmRpeDZ1SHZ4Q1hqWnJtYWFPMEdpUmV5?=
 =?utf-8?B?UzR1cm1wYnJlMDRSSVZmQm55UHN2SjYwaGtrRjRDWTRQcVZBcTFhdDFZQUVM?=
 =?utf-8?B?c29BeWhWTVNGZnBkcEJMeFhqWmRPeVk1UFRPNTlDeHlpRC9ZcFAvM1c1b3JN?=
 =?utf-8?B?VkJmSi9PejdPRGtNVGtrSnB0czhzblpTMTVEeVEzdXQ2Q2ptdnEzRXpxVURT?=
 =?utf-8?B?dmg4TER0Skt6VE1BT1dBVTlqYnAxVDY3Q0ZMT0RrRnJkRnR2UT09?=
X-OriginatorOrg: oracle.com
X-MS-Exchange-CrossTenant-Network-Message-Id: 151e7b1f-f69e-4b36-b2b3-08dbbb07499e
X-MS-Exchange-CrossTenant-AuthSource: SJ0PR10MB4542.namprd10.prod.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 22 Sep 2023 01:00:17.9285
 (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: C2xUv1uyxmyKsSDzWH11MmomQ5PEFLgfaqPGgdYC193kco8E0mtbgWceGRk5LZGUUZAWGOke4JkObyadMSobAPoUZ2Mklas/kQVSFSqmwNA=
X-MS-Exchange-Transport-CrossTenantHeadersStamped: PH7PR10MB6457
X-Proofpoint-Virus-Version: vendor=baseguard
 engine=ICAP:2.0.267,Aquarius:18.0.980,Hydra:6.0.619,FMLib:17.11.176.26
 definitions=2023-09-21_21,2023-09-21_01,2023-05-22_02
X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 adultscore=0 malwarescore=0 spamscore=0
 suspectscore=0 mlxlogscore=832 phishscore=0 mlxscore=0 bulkscore=0
 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2309180000
 definitions=main-2309220007
X-Proofpoint-GUID: b-grOEAUxUg4VA-SmHnFbKc0MsYa_W3e
X-Proofpoint-ORIG-GUID: b-grOEAUxUg4VA-SmHnFbKc0MsYa_W3e
X-Spam-Status: No, score=-3.6 required=5.0 tests=BAYES_00,DKIM_SIGNED,
        DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,NICE_REPLY_A,
        RCVD_IN_DNSWL_BLOCKED,RCVD_IN_MSPIKE_H5,RCVD_IN_MSPIKE_WL,
        SPF_HELO_NONE,SPF_NONE 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
X-Greylist: Sender passed SPF test, not delayed by milter-greylist-4.6.4 (snail.vger.email [0.0.0.0]); Thu, 21 Sep 2023 18:00:43 -0700 (PDT)


On 9/21/23 19:22, Andrew Morton wrote:
> On Thu, 21 Sep 2023 17:59:38 -0400 Eric DeVolder <eric.devolder@oracle.com> wrote:
> 
>> Scaled up testing has revealed that the kexec_trylock()
>> implementation leads to failures within the crash hotplug
>> infrastructure due to the inability to acquire the lock,
>> specifically the message:
>>
>> ...
>>
>> Convert the atomic lock to a mutex.
>>
> 
> Do you think this problem is serious enough to warrant a backport into
> -stable kernels?

I do not since it will be the lock traffic created by the crash hotplug infrastructure that will 
reveal the weak locking mechanism. Until this crash hotplug shows up in a stable kernel, it should 
not be an issue; there isn't anything else that easily exercise it to reveal the problem.

eric