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X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 17 Dec 2025 13:57:13.9466 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 328a592c-33d9-4312-0fb9-08de3d742e96 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: DB3PEPF00008860.eurprd02.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: AM8PR08MB6484 X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 58DABC000A X-Stat-Signature: dgdtygazbims5szx3rpxe85erofohy44 X-Rspam-User: X-HE-Tag: 1765979844-742965 X-HE-Meta: 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 wLNKEgrI 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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: [...] > > Note this is explained in Documentation/core-api/real-time/differences.rst: > > > > Memory allocation > > ----------------- > > > > The memory allocation APIs, such as kmalloc() and alloc_pages(), require a > > gfp_t flag to indicate the allocation context. On non-PREEMPT_RT kernels, it is > > necessary to use GFP_ATOMIC when allocating memory from interrupt context or > > from sections where preemption is disabled. This is because the allocator must > > not sleep in these contexts waiting for memory to become available. > > > > However, this approach does not work on PREEMPT_RT kernels. The memory > > allocator in PREEMPT_RT uses sleeping locks internally, which cannot be > > acquired when preemption is disabled. Fortunately, this is generally not a > > problem, because PREEMPT_RT moves most contexts that would traditionally run > > with preemption or interrupts disabled into threaded context, where sleeping is > > allowed. > > > > What remains problematic is code that explicitly disables preemption or > > interrupts. In such cases, memory allocation must be performed outside the > > critical section. > > > > This restriction also applies to memory deallocation routines such as kfree() > > and free_pages(), which may also involve internal locking and must not be > > called from non-preemptible contexts. > > Oh, thanks for pointing to that, I had never read that before (oops). > > Shall we point to this from the doc-comment? Something like the below. > > BTW, Yeorum, assuming you care about PREEMPT_RT, maybe you can get > Sparse to find some other bugs of this nature? Or if not, plain old > Coccinelle would probably find a few. That's good idea. I'll try to sparse later. Although this is a slightly different topic, based on Ryan’s suggestion, I plan to address this misuse on arm64 by switching to pre-allocated pages. As a result, I will remove the pgtable_alloc_nolock() interface. > From 4c6b4d4cb08aee9559d02a348b9ecf799142c96f Mon Sep 17 00:00:00 2001 > From: Brendan Jackman > Date: Wed, 17 Dec 2025 13:26:28 +0000 > Subject: [PATCH] mm: clarify GFP_ATOMIC/GFP_NOWAIT doc-comment > > The current description of contexts where it's invalid to make > GFP_ATOMIC and GFP_NOWAIT calls is rather vague. > > Replace this with a direct description of the actual contexts of concern > and refer to the RT docs where this is explained more discursively. > > While rejigging this prose, also move the documentation of GFP_NOWAIT to > the GFP_NOWAIT section. > > Link: https://lore.kernel.org/all/d912480a-5229-4efe-9336-b31acded30f5@suse.cz/ > Signed-off-by: Brendan Jackman > --- > include/linux/gfp_types.h | 7 +++++-- > 1 file changed, 5 insertions(+), 2 deletions(-) > > diff --git a/include/linux/gfp_types.h b/include/linux/gfp_types.h > index 3de43b12209ee..07a378542caf2 100644 > --- a/include/linux/gfp_types.h > +++ b/include/linux/gfp_types.h > @@ -309,8 +309,10 @@ enum { > * > * %GFP_ATOMIC users can not sleep and need the allocation to succeed. A lower > * watermark is applied to allow access to "atomic reserves". > - * The current implementation doesn't support NMI and few other strict > - * non-preemptive contexts (e.g. raw_spin_lock). The same applies to %GFP_NOWAIT. > + * The current implementation doesn't support NMI, nor contexts that disable > + * preemption under PREEMPT_RT. This includes raw_spin_lock() and plain > + * preempt_disable() - see Documentation/core-api/real-time/differences.rst for > + * more info. > * > * %GFP_KERNEL is typical for kernel-internal allocations. The caller requires > * %ZONE_NORMAL or a lower zone for direct access but can direct reclaim. > @@ -321,6 +323,7 @@ enum { > * %GFP_NOWAIT is for kernel allocations that should not stall for direct > * reclaim, start physical IO or use any filesystem callback. It is very > * likely to fail to allocate memory, even for very small allocations. > + * The same restrictions on calling contexts apply as for %GFP_ATOMIC. > * > * %GFP_NOIO will use direct reclaim to discard clean pages or slab pages > * that do not require the starting of any physical IO. > -- > 2.50.1 This patch looks good to me. Feel free to add: Reviewed-by: Yeoreum Yun -- Sincerely, Yeoreum Yun