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X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 15 Dec 2025 10:07:46.5160 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: a26f722a-8b62-479f-26e3-08de3bc1cbb8 X-MS-Exchange-CrossTenant-Id: f34e5979-57d9-4aaa-ad4d-b122a662184d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=f34e5979-57d9-4aaa-ad4d-b122a662184d;Ip=[4.158.2.129];Helo=[outbound-uk1.az.dlp.m.darktrace.com] X-MS-Exchange-CrossTenant-AuthSource: DB1PEPF000509F1.eurprd03.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: PA4PR08MB7642 > On Mon Dec 15, 2025 at 9:34 AM UTC, Yeoreum Yun wrote: > > Hi Brendan, > >> On Sun Dec 14, 2025 at 9:13 AM UTC, Yeoreum Yun wrote: > >> >> I don't have the context on what this code is doing so take this with > >> >> a grain of salt, but... > >> >> > >> >> The point of the _nolock alloc is to give the allocator an excuse to > >> >> fail. Panicking on that failure doesn't seem like a great idea to me? > >> > > >> > I thought first whether it changes to "static" memory area to handle > >> > this in PREEMPT_RT. > >> > But since this function is called while smp_cpus_done(). > >> > So, I think it's fine since there wouldn't be a contention for > >> > memory allocation in this phase. > >> > >> Then shouldn't it use _nolock unconditionally? > > > > As you pointed out, I think it should be fine even in the !PREEMPT_RT case. > > However, in case I missed something or if my understanding is incorrect, > > I applied it only to the PREEMPT_RT case for now. > > Hmm, I don't think "this code might be broken so let's cage it behind a > conditional" is a good strategy. > > 1. It bloats the codebase. > > 2. It's confusing to readers, now you have to try an understand why this > conditional is here, which is a doomed effort. This could be > mitigated with comments but, see point 1. > > 3. It expands the testing matrix. So now we have code that we aren't > really sure is correct, AND it gets less test coverage. > > Overall I am feeling a bit uncomfortable about this use of _nolock, but > I am also feeling pretty ignorant about PREEMPT_RT and also about this > arm64 code, so I am hesitant to suggest alternatives, I hope someone > else can offer some input here... I understand. However, as I mentioned earlier, my main intention was to hear opinions specifically about memory contention. That said, if there is no memory contention, I don’t think using the _nolock API is necessarily a bad approach. In fact, I believe a bigger issue is that, under PREEMPT_RT, code that uses the regular memory allocation APIs may give users the false impression that those APIs are “safe to use,” even though they are not. -- Sincerely, Yeoreum Yun