Merge branch 'x86-asm-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git...

[linux-2.6-microblaze.git] / arch / x86 / kernel / irq.c

diff --git a/arch/x86/kernel/irq.c b/arch/x86/kernel/irq.c
index c7dfe1b..4616672 100644 (file)
--- 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.
+        */
+
        entering_irq();
 
+       /* entering_irq() tells RCU that we're not quiescent.  Check it. */
+       RCU_LOCKDEP_WARN(!rcu_is_watching(), "IRQ failed to wake up RCU");
+
        irq = __this_cpu_read(vector_irq[vector]);
 
        if (!handle_irq(irq, regs)) {