Messages in this thread | | | Date | Wed, 15 Jul 2015 01:26:21 +0200 | From | Frederic Weisbecker <> | Subject | Re: [tip:x86/asm] x86/irq, context_tracking: Document how IRQ context tracking works and add an RCU assertion |
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On Tue, Jul 07, 2015 at 03:54:32AM -0700, tip-bot for Andy Lutomirski wrote: > Commit-ID: 0333a209cbf600e980fc55c24878a56f25f48b65 > Gitweb: http://git.kernel.org/tip/0333a209cbf600e980fc55c24878a56f25f48b65 > Author: Andy Lutomirski <luto@kernel.org> > AuthorDate: Fri, 3 Jul 2015 12:44:34 -0700 > Committer: Ingo Molnar <mingo@kernel.org> > CommitDate: Tue, 7 Jul 2015 10:59:10 +0200 > > x86/irq, context_tracking: Document how IRQ context tracking works and add an RCU assertion > > Signed-off-by: Andy Lutomirski <luto@kernel.org> > Cc: Andy Lutomirski <luto@amacapital.net> > Cc: Borislav Petkov <bp@alien8.de> > Cc: Brian Gerst <brgerst@gmail.com> > Cc: Denys Vlasenko <dvlasenk@redhat.com> > Cc: Denys Vlasenko <vda.linux@googlemail.com> > Cc: Frederic Weisbecker <fweisbec@gmail.com> > Cc: H. Peter Anvin <hpa@zytor.com> > Cc: Kees Cook <keescook@chromium.org> > Cc: Linus Torvalds <torvalds@linux-foundation.org> > Cc: Oleg Nesterov <oleg@redhat.com> > Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> > Cc: Peter Zijlstra <peterz@infradead.org> > Cc: Rik van Riel <riel@redhat.com> > Cc: Thomas Gleixner <tglx@linutronix.de> > Cc: paulmck@linux.vnet.ibm.com > Link: http://lkml.kernel.org/r/e8bdc4ed0193fb2fd130f3d6b7b8023e2ec1ab62.1435952415.git.luto@kernel.org > Signed-off-by: Ingo Molnar <mingo@kernel.org> > --- > arch/x86/kernel/irq.c | 15 +++++++++++++++ > 1 file changed, 15 insertions(+) > > diff --git a/arch/x86/kernel/irq.c b/arch/x86/kernel/irq.c > index 88b36648..6233de0 100644 > --- a/arch/x86/kernel/irq.c > +++ b/arch/x86/kernel/irq.c > @@ -216,8 +216,23 @@ __visible unsigned int __irq_entry do_IRQ(struct pt_regs *regs) > unsigned vector = ~regs->orig_ax; > unsigned irq; > > + /* > + * NB: Unlike exception entries, IRQ entries do not reliably > + * handle context tracking in the low-level entry code. This is > + * because syscall entries execute briefly with IRQs on before > + * updating context tracking state, so we can take an IRQ from > + * kernel mode with CONTEXT_USER. The low-level entry code only > + * updates the context if we came from user mode, so we won't > + * switch to CONTEXT_KERNEL. We'll fix that once the syscall > + * code is cleaned up enough that we can cleanly defer enabling > + * IRQs. > + */ > +
Now is it a problem to take interrupts in kernel mode with CONTEXT_USER? I'm not sure it's worth trying to make it not happen.
> entering_irq(); > > + /* entering_irq() tells RCU that we're not quiescent. Check it. */ > + rcu_lockdep_assert(rcu_is_watching(), "IRQ failed to wake up RCU");
Why do we need to check that?
> + > irq = __this_cpu_read(vector_irq[vector]); > > if (!handle_irq(irq, regs)) {
Thanks.
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