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[103.168.172.200]) by smtp.gmail.com with ESMTPSA id af79cd13be357-7b18d279103sm288003385a.16.2024.10.27.21.38.44 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 27 Oct 2024 21:38:44 -0700 (PDT) Received: from phl-compute-03.internal (phl-compute-03.phl.internal [10.202.2.43]) by mailfauth.phl.internal (Postfix) with ESMTP id C367A1200068; Mon, 28 Oct 2024 00:38:43 -0400 (EDT) Received: from phl-mailfrontend-01 ([10.202.2.162]) by phl-compute-03.internal (MEProxy); Mon, 28 Oct 2024 00:38:43 -0400 X-ME-Sender: X-ME-Received: X-ME-Proxy-Cause: gggruggvucftvghtrhhoucdtuddrgeeftddrvdejjedgjeegucetufdoteggodetrfdotf fvucfrrhhofhhilhgvmecuhfgrshhtofgrihhlpdggtfgfnhhsuhgsshgtrhhisggvpdfu rfetoffkrfgpnffqhgenuceurghilhhouhhtmecufedttdenucesvcftvggtihhpihgvnh htshculddquddttddmnecujfgurhepfffhvfevuffkfhggtggujgesthdtredttddtvden ucfhrhhomhepuehoqhhunhcuhfgvnhhguceosghoqhhunhdrfhgvnhhgsehgmhgrihhlrd gtohhmqeenucggtffrrghtthgvrhhnpefhtedvgfdtueekvdekieetieetjeeihedvteeh uddujedvkedtkeefgedvvdehtdenucffohhmrghinhepkhgvrhhnvghlrdhorhhgnecuve hluhhsthgvrhfuihiivgeptdenucfrrghrrghmpehmrghilhhfrhhomhepsghoqhhunhdo mhgvshhmthhprghuthhhphgvrhhsohhnrghlihhthidqieelvdeghedtieegqddujeejke ehheehvddqsghoqhhunhdrfhgvnhhgpeepghhmrghilhdrtghomhesfhhigihmvgdrnhgr mhgvpdhnsggprhgtphhtthhopedvuddpmhhouggvpehsmhhtphhouhhtpdhrtghpthhtoh epfhhujhhithgrrdhtohhmohhnohhrihesghhmrghilhdrtghomhdprhgtphhtthhopegr nhhnrgdqmhgrrhhirgeslhhinhhuthhrohhnihigrdguvgdprhgtphhtthhopehfrhgvug gvrhhitgeskhgvrhhnvghlrdhorhhgpdhrtghpthhtohepthhglhigsehlihhnuhhtrhho nhhigidruggvpdhrtghpthhtohepjhhsthhulhhtiiesghhoohhglhgvrdgtohhmpdhrtg hpthhtohepshgsohihugeskhgvrhhnvghlrdhorhhgpdhrtghpthhtoheplhhinhhugidq khgvrhhnvghlsehvghgvrhdrkhgvrhhnvghlrdhorhhgpdhrtghpthhtohepnhgvthguvg hvsehvghgvrhdrkhgvrhhnvghlrdhorhhgpdhrtghpthhtoheprhhushhtqdhfohhrqdhl ihhnuhigsehvghgvrhdrkhgvrhhnvghlrdhorhhg X-ME-Proxy: Feedback-ID: iad51458e:Fastmail Received: by mail.messagingengine.com (Postfix) with ESMTPA; Mon, 28 Oct 2024 00:38:43 -0400 (EDT) Date: Sun, 27 Oct 2024 21:38:41 -0700 From: Boqun Feng To: FUJITA Tomonori Cc: anna-maria@linutronix.de, frederic@kernel.org, tglx@linutronix.de, jstultz@google.com, sboyd@kernel.org, linux-kernel@vger.kernel.org, netdev@vger.kernel.org, rust-for-linux@vger.kernel.org, andrew@lunn.ch, hkallweit1@gmail.com, tmgross@umich.edu, ojeda@kernel.org, alex.gaynor@gmail.com, gary@garyguo.net, bjorn3_gh@protonmail.com, benno.lossin@proton.me, a.hindborg@samsung.com, aliceryhl@google.com, arnd@arndb.de Subject: Re: [PATCH v4 4/7] rust: time: Add wrapper for fsleep function Message-ID: References: <20241025033118.44452-1-fujita.tomonori@gmail.com> <20241025033118.44452-5-fujita.tomonori@gmail.com> <20241028.095030.2023085589483262207.fujita.tomonori@gmail.com> Precedence: bulk X-Mailing-List: rust-for-linux@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20241028.095030.2023085589483262207.fujita.tomonori@gmail.com> On Mon, Oct 28, 2024 at 09:50:30AM +0900, FUJITA Tomonori wrote: > On Fri, 25 Oct 2024 15:03:37 -0700 > Boqun Feng wrote: > > >> +/// Sleeps for a given duration at least. > >> +/// > >> +/// Equivalent to the kernel's [`fsleep`], flexible sleep function, > >> +/// which automatically chooses the best sleep method based on a duration. > >> +/// > >> +/// The function sleeps infinitely (MAX_JIFFY_OFFSET) if `Delta` is negative > >> +/// or exceedes i32::MAX milliseconds. > >> +/// > > > > I know Miguel has made his suggestion: > > > > https://lore.kernel.org/rust-for-linux/CANiq72kWqSCSkUk1efZyAi+0ScNTtfALn+wiJY_aoQefu2TNvg@mail.gmail.com/ > > > > , but I think what we should really do here is just panic if `Delta` is > > negative or exceedes i32::MAX milliseconds, and document clearly that > > this function expects `Delta` to be in a certain range, i.e. it's the > > user's responsibility to check. Because: > > > > * You can simply call schedule() with task state set properly to > > "sleep infinitely". > > > > * Most of the users of fsleep() don't need this "sleep infinitely" > > functionality. Instead, they want to sleep with a reasonable > > short time. > > I agree with the above reasons but I'm not sure about just panic with > a driver's invalid argument. > If a driver blindly trusts a user-space input or a value chosen by the hardware, I would say it's a bug in the driver. So IMO drivers should check the input of fsleep(). > Can we just return an error instead? > That also works for me, but an immediate question is: do we put #[must_use] on `fsleep()` to enforce the use of the return value? If yes, then the normal users would need to explicitly ignore the return value: let _ = fsleep(1sec); The "let _ =" would be a bit annoying for every user that just uses a constant duration. If no, then a user with incorrect input can just skip the return value check: fsleep(duration_based_on_user_input); Would it be an issue? For example, you put an fsleep() in the loop and expect it at least sleep for a bit time, however, a craft user input can cause the sleep never happen, and as a result, turn the loop into a busy waiting. All I'm trying to say is that 99% users of fsleep() will just use a constant and small value, it seems a bit over-doing to me to return an error just for the <1% users in theory that don't check the input. But that's not a blocker from me. > >> +/// This function can only be used in a nonatomic context. > >> +pub fn fsleep(delta: time::Delta) { > >> + // SAFETY: FFI call. > >> + unsafe { > >> + // Convert the duration to microseconds and round up to preserve > >> + // the guarantee; fsleep sleeps for at least the provided duration, > >> + // but that it may sleep for longer under some circumstances. > >> + bindings::fsleep(delta.as_micros_ceil() as c_ulong) > > > > If delta is 0x10000_0000i64 * 1000_000 (=0xf424000000000i64), which > > exceeds i32::MAX milliseconds, the result of `delta.as_micros_ceil() as > > c_ulong` is: > > > > * 0 on 32bit > > * 0x3e800000000 on 64bit > > > > , if I got my math right. The first is obviously not "sleeps > > infinitely". > > > > Continue on 64bit case, in C's fsleep(), 0x3e800000000 will be cast to > > "int" (to call msleep()), which results as 0, still not "sleep > > infinitely"? > > You mean "unsigned int" (to call msleep())? > Ah, yes. > You are correct that we can't say "the function sleeps infinitely > (MAX_JIFFY_OFFSET) if `Delta` is negative or exceeds i32::MAX > milliseconds.". There are some exceptional ranges. > > Considering that Rust-for-Linux might eventually support 32-bit > systems, fsleep's arguments must be less than u32::MAX (usecs). > Additionally, Because of DIV_ROUND_UP (to call msleep()), it must be > less than u32::MAX - 1000. To simplify the expression, the maximum > Delta is u32::MAX / 2 (usecs)? I think that it's long enough for > the users of fsleep(). > Agreed. Though I'm attempting to make msleep() takes a `unsigned long`, but I already have a lot in my plate... Regards, Boqun