powerpc/irq: Don't switch to irq stack from softirq stack

irq_exit() is now called on the irq stack, which can trigger a switch to
the softirq stack from the irq stack.  If an interrupt happens at that
point, we will not properly detect the re-entrancy and clobber the
original return context on the irq stack.

This fixes it.  The side effect is to prevent all nesting from softirq
stack to irq stack even in the "safe" case but it's simpler that way and
matches what x86_64 does.

Reported-by: Cédric Le Goater <clg@fr.ibm.com>
Tested-by: Cédric Le Goater <clg@fr.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 3 insertions, 2 deletions

diff --git a/arch/powerpc/kernel/irq.c b/arch/powerpc/kernel/irq.c
index 57d286a78f86..c7cb8c232d2f 100644
--- a/arch/powerpc/kernel/irq.c
+++ b/arch/powerpc/kernel/irq.c
@@ -495,14 +495,15 @@ void __do_irq(struct pt_regs *regs)
 void do_IRQ(struct pt_regs *regs)
 {
         struct pt_regs *old_regs = set_irq_regs(regs);
-        struct thread_info *curtp, *irqtp;
+        struct thread_info *curtp, *irqtp, *sirqtp;
 
         /* Switch to the irq stack to handle this */
         curtp = current_thread_info();
         irqtp = hardirq_ctx[raw_smp_processor_id()];
+        sirqtp = softirq_ctx[raw_smp_processor_id()];
 
         /* Already there ? */
-        if (unlikely(curtp == irqtp)) {
+        if (unlikely(curtp == irqtp || curtp == sirqtp)) {
                 __do_irq(regs);
                 set_irq_regs(old_regs);
                 return;