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Hallyn" Cc: Alice Ryhl , Paul Moore , James Morris , Miguel Ojeda , Christian Brauner , Alex Gaynor , Wedson Almeida Filho , Boqun Feng , =?UTF-8?B?QmrDtnJu?= Roy Baron , Benno Lossin , Andreas Hindborg , Peter Zijlstra , Alexander Viro , Greg Kroah-Hartman , Arve =?UTF-8?B?SGrDuG5uZXbDpWc=?= , Todd Kjos , Martijn Coenen , Joel Fernandes , Carlos Llamas , Suren Baghdasaryan , Dan Williams , Matthew Wilcox , Thomas Gleixner , Daniel Xu , Martin Rodriguez Reboredo , Trevor Gross , linux-kernel@vger.kernel.org, linux-security-module@vger.kernel.org, rust-for-linux@vger.kernel.org, linux-fsdevel@vger.kernel.org, Kees Cook Subject: Re: [PATCH v10 1/8] rust: types: add `NotThreadSafe` Message-ID: <20240927112021.051bcc6a@eugeo> In-Reply-To: <20240925135904.GA654417@mail.hallyn.com> References: <20240915-alice-file-v10-0-88484f7a3dcf@google.com> <20240915-alice-file-v10-1-88484f7a3dcf@google.com> <20240924194540.GA636453@mail.hallyn.com> <20240925135904.GA654417@mail.hallyn.com> X-Mailer: Claws Mail 4.2.0 (GTK 3.24.43; 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Hallyn" wrote: > On Wed, Sep 25, 2024 at 01:06:10PM +0200, Alice Ryhl wrote: > > On Tue, Sep 24, 2024 at 9:45=E2=80=AFPM Serge E. Hallyn wrote: =20 > > > > > > On Sun, Sep 15, 2024 at 02:31:27PM +0000, Alice Ryhl wrote: =20 > > > > This introduces a new marker type for types that shouldn't be threa= d > > > > safe. By adding a field of this type to a struct, it becomes non-Se= nd > > > > and non-Sync, which means that it cannot be accessed in any way fro= m > > > > threads other than the one it was created on. > > > > > > > > This is useful for APIs that require globals such as `current` to r= emain > > > > constant while the value exists. > > > > > > > > We update two existing users in the Kernel to use this helper: > > > > > > > > * `Task::current()` - moving the return type of this value to a > > > > different thread would not be safe as you can no longer be guara= nteed > > > > that the `current` pointer remains valid. > > > > * Lock guards. Mutexes and spinlocks should be unlocked on the sam= e > > > > thread as where they were locked, so we enforce this using the S= end > > > > trait. =20 > > > > > > Hi, > > > > > > this sounds useful, however from kernel side when I think thread-safe= , > > > I think must not be used across a sleep. Would something like Thread= Locked > > > or LockedToThread make sense? =20 > >=20 > > Hmm, those names seem pretty similar to the current name to me? =20 >=20 > Seems very different to me: >=20 > If @foo is not threadsafe, it may be global or be usable by many > threads, but must be locked to one thread during access. >=20 > What you're describing here is (iiuc) that @foo must only be used > by one particular thread. "locked to one thread during access" means it might be `Send` but not `!Sync`. What Alice has here is something is neither `Send` nor `Sync`, so I think the `NotThreadSafe` is a good name here because it cancels both guarantees. Best, Gary