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charset=UTF-8 Date: Fri, 02 Oct 2026 21:12:31 +0900 Message-Id: Cc: "Gary Guo" , "Danilo Krummrich" , "Timur Tabi" , "Alistair Popple" , "Eliot Courtney" , "Zhi Wang" , "David Airlie" , "Simona Vetter" , "Bjorn Helgaas" , "Miguel Ojeda" , "Alex Gaynor" , "Boqun Feng" , =?utf-8?q?Bj=C3=B6rn_Roy_Baron?= , "Benno Lossin" , "Andreas Hindborg" , "Alice Ryhl" , "Trevor Gross" , , "LKML" , "Joel Fernandes" Subject: Re: [PATCH v5 02/15] rust: sync: completion: add wait_for_completion_timeout() From: "Alexandre Courbot" To: "John Hubbard" References: <20260930034148.590687-1-jhubbard@nvidia.com> <20260930034148.590687-3-jhubbard@nvidia.com> <59900705-fadd-46bb-93eb-8f6d8e7be551@nvidia.com> In-Reply-To: <59900705-fadd-46bb-93eb-8f6d8e7be551@nvidia.com> X-ClientProxiedBy: TYWPR01CA0048.jpnprd01.prod.outlook.com (2603:1096:400:17f::18) To MW4PR12MB6873.namprd12.prod.outlook.com (2603:10b6:303:20c::17) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: MW4PR12MB6873:EE_|BL4PR12MB9721:EE_ X-MS-Office365-Filtering-Correlation-Id: 366b01a4-7e0b-45f2-daa3-08df207e7139 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|10070799003|376014|7416014|23010399003|366016|13003099007|22082099003|18002099003|6133799003|56012099006|4143699003|11063799006|10067099003; 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Add a timeout variant of >>>> wait_for_completion(). >>>> >>>> Reviewed-by: Alexandre Courbot >>>> Signed-off-by: Joel Fernandes >>>> [jhubbard: return the remaining jiffies] >>>> Signed-off-by: John Hubbard >>> >>> This email should have RfL list CC'ed. > > Hi Gary! Apologies, my send-email scripts had drifted into a > nova-centric direction. Will fix. > > >>> >>>> --- >>>> rust/kernel/sync/completion.rs | 23 ++++++++++++++++++++++- >>>> 1 file changed, 22 insertions(+), 1 deletion(-) >>>> >>>> diff --git a/rust/kernel/sync/completion.rs b/rust/kernel/sync/complet= ion.rs >>>> index 35ff049ff078..7e8b3c1c880e 100644 >>>> --- a/rust/kernel/sync/completion.rs >>>> +++ b/rust/kernel/sync/completion.rs >>>> @@ -6,7 +6,12 @@ >>>> //! >>>> //! C header: [`include/linux/completion.h`](srctree/include/linux/co= mpletion.h) >>>> =20 >>>> -use crate::{bindings, prelude::*, types::Opaque}; >>>> +use crate::{ >>>> + bindings, >>>> + prelude::*, >>>> + time::Jiffies, >>>> + types::Opaque, // >>>> +}; >>>> =20 >>>> /// Synchronization primitive to signal when a certain task has been = completed. >>>> /// >>>> @@ -111,4 +116,20 @@ pub fn wait_for_completion(&self) { >>>> // SAFETY: `self.as_raw()` is a pointer to a valid `struct co= mpletion`. >>>> unsafe { bindings::wait_for_completion(self.as_raw()) }; >>>> } >>>> + >>>> + /// Wait for completion of a task, with a timeout. >>>> + /// >>>> + /// This method waits for the completion of a task, or until `tim= eout` elapses. It is not >>>> + /// interruptible. Returns the number of jiffies left when the ta= sk completed, or [`None`] if >>>> + /// `timeout` elapsed first. >>>> + /// >>>> + /// See also [`Completion::complete_all`]. >>>> + #[inline] >>>> + pub fn wait_for_completion_timeout(&self, timeout: Jiffies) -> Op= tion { >>> >>> NACK. Please use the typed `Delta`, not this old type alias for = c_ulong. >>> I asked Miguel to take that late last cycle because I know there'll be = new users >>> that want to use Jiffies this cycle! >>> >>> This would avoid you having to do clamping on the max side (but you sti= ll need >>> to clamp the value to be at least 0). There'll be a helper method for t= his, but >>> it isn't available yet. >>> https://lore.kernel.org/rust-for-linux/20261002050428.2746277-3-tomo@fl= apping.org/ >>=20 >> I will drop this patch and replace the code using this new method (which >> is just an optional probe-time self-test) by a polling loop on an >> atomic. That way we can wait for the helper method to be available and >> revisit this with the proper type. > > OK, whatever works best. Just in case, I did stage a fixed-up version > of the patch locally (in case I need to send a v6), as per Gary's > recommended Delta approach. It looks like this: It's your series so your call, but since the elegant solution will involve using [1] which is still under review, I would suggest waiting for it to introduce `wait_for_completion_timeout`, moving forward with the rest of the series, and revisit using completions once the base code is ready to limit churn. Otherwise we are at risk of missing the -rc6 cutoff for this series and that means an even busier next cycle. The polling code is also simpler overall than using completions, and for a probe-time selftest polling is really not a problem. Nova is not losing anything by not using completions for this. [1] https://lore.kernel.org/rust-for-linux/20261002050428.2746277-3-tomo@fl= apping.org/