Date: Mon, 11 Jul 2016 09:42:42 -0700 From: Linus Torvalds <torvalds@...ux-foundation.org> To: Mark Rutland <mark.rutland@....com> Cc: Andy Lutomirski <luto@...capital.net>, "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>, Nadav Amit <nadav.amit@...il.com>, Kees Cook <keescook@...omium.org>, Borislav Petkov <bp@...en8.de>, Josh Poimboeuf <jpoimboe@...hat.com>, X86 ML <x86@...nel.org>, Jann Horn <jann@...jh.net>, Heiko Carstens <heiko.carstens@...ibm.com>, Brian Gerst <brgerst@...il.com>, "kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org> Subject: Re: [PATCH v4 26/29] sched: Allow putting thread_info into task_struct On Mon, Jul 11, 2016 at 9:31 AM, Mark Rutland <mark.rutland@....com> wrote: >> >> So until you do the wire that actually disables preemption you can >> schedule away as much as you want, and after that write you no longer >> will. > > I was assuming a percpu pointer to current (or preempt count). So for the same reason that is ok *iff* you have - some kind of dedicated percpu register (or other base pointer - x86 has the segment thing) that gets updated when you schedule. - an instruction that can load 'current' directly off that register atomically. But yes, percpu data in general is obviously not safe to access without preemption. Linus
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