1 files changed, 6 insertions, 1 deletions

diff --git a/arch/x86_64/kernel/entry.S b/arch/x86_64/kernel/entry.S
index 4fcc0ad8bbeb..ea32688386fd 100644
--- a/arch/x86_64/kernel/entry.S
+++ b/arch/x86_64/kernel/entry.S
@@ -519,7 +519,12 @@ END(stub_rt_sigreturn)
         testl $3,CS(%rdi)
         je 1f
         swapgs  
-1:      incl    %gs:pda_irqcount        # RED-PEN should check preempt count
+        /* irqcount is used to check if a CPU is already on an interrupt
+           stack or not. While this is essentially redundant with preempt_count
+           it is a little cheaper to use a separate counter in the PDA
+           (short of moving irq_enter into assembly, which would be too
+            much work) */
+1:      incl    %gs:pda_irqcount
         cmoveq %gs:pda_irqstackptr,%rsp
         push    %rbp                    # backlink for old unwinder
         /*