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X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 08 Jun 2025 13:33:49.0953 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 2a94e947-c398-43d6-cb4a-08dda69119e4 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: DB3PEPF0000885C.eurprd02.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: DU0PR08MB7464 X-Stat-Signature: orcuxc8iw9kpowpz7a7dseig18qpu46u X-Rspamd-Queue-Id: 65E3040008 X-Rspam-User: X-Rspamd-Server: rspam02 X-HE-Tag: 1749389637-372213 X-HE-Meta: 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 hpL18S13 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 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: List-Subscribe: List-Unsubscribe: Hi mm experts, I have a (possibly silly) question regarding the use of memory allocation w= ith GFP_ATOMIC. According to the latest documentation in core-api/memory-allocation.html, using GFP_ATOMIC is acceptable in interrupt handlers: GFP_ATOMIC: =93(GFP_KERNEL | __GFP_HIGH) & ~__GFP_DIRECT_RECLAIM (aka GFP_ATOMIC) =96 non-sleeping allocation with an expensive fallback, so it can access some portion of memory reserves. Usually used from interrupt/bottom-half context with an expensive slow path= fallback.=94 This makes sense on non-RT kernels, where spin_lock() is non-sleepable. However, how does this behave on a PREEMPT_RT kernel? >From what I see in the buddy allocator, even allocations using GFP_ATOMIC can potentially sleep, since some of the locks used (e.g., zone->lock) are implemented as sleepable rtmutex under PREEMPT_RT. This seems fine for most interrupt handlers, since on PREEMPT_RT, they are handled in dedicated IRQ threads =97 which means they run in a sle= epable context. But what about interrupt handlers registered with IRQF_NO_THREAD? Those handlers run in hard interrupt context, which is non-sleepable. If an allocation with GFP_ATOMIC involves a sleepable lock (like zone->lock= ), wouldn=92t that be problematic? To my knowledge, it=92s not clearly documented whether memory allocation fu= nctions like kmalloc(), alloc_pages(), or folio_alloc() are explicitly forbidden in trul= y non-sleepable contexts under PREEMPT_RT. So my question is: Is it always safe to call GFP_ATOMIC allocations from a non-sleepable conte= xt, regardless of the kernel configuration (i.e., RT vs non-RT)? Thanks! IMPORTANT NOTICE: The contents of this email and any attachments are confid= ential and may also be privileged. If you are not the intended recipient, p= lease notify the sender immediately and do not disclose the contents to any= other person, use it for any purpose, or store or copy the information in = any medium. Thank you.