powerpc/irq: Run softirqs off the top of the irq stack

Nowadays, irq_exit() calls __do_softirq() pretty much directly
instead of calling do_softirq() which switches to the decicated
softirq stack.

This has lead to observed stack overflows on powerpc since we call
irq_enter() and irq_exit() outside of the scope that switches to
the irq stack.

This fixes it by moving the stack switching up a level, making
irq_enter() and irq_exit() run off the irq stack.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

4 files changed, 62 insertions, 65 deletions

diff --git a/arch/powerpc/include/asm/irq.h b/arch/powerpc/include/asm/irq.h
index 0e40843a1c6e..41f13cec8a8f 100644
--- a/arch/powerpc/include/asm/irq.h
+++ b/arch/powerpc/include/asm/irq.h
@@ -69,9 +69,9 @@ extern struct thread_info *softirq_ctx[NR_CPUS];
 
 extern void irq_ctx_init(void);
 extern void call_do_softirq(struct thread_info *tp);
-extern int call_handle_irq(int irq, void *p1,
-                           struct thread_info *tp, void *func);
+extern void call_do_irq(struct pt_regs *regs, struct thread_info *tp);
 extern void do_IRQ(struct pt_regs *regs);
+extern void __do_irq(struct pt_regs *regs);
 
 int irq_choose_cpu(const struct cpumask *mask);
 
diff --git a/arch/powerpc/kernel/irq.c b/arch/powerpc/kernel/irq.c
index c69440cef7af..2234a1276a77 100644
--- a/arch/powerpc/kernel/irq.c
+++ b/arch/powerpc/kernel/irq.c
@@ -441,50 +441,6 @@ void migrate_irqs(void)
 }
 #endif
 
-static inline void handle_one_irq(unsigned int irq)
-{
-        struct thread_info *curtp, *irqtp;
-        unsigned long saved_sp_limit;
-        struct irq_desc *desc;
-
-        desc = irq_to_desc(irq);
-        if (!desc)
-                return;
-
-        /* Switch to the irq stack to handle this */
-        curtp = current_thread_info();
-        irqtp = hardirq_ctx[smp_processor_id()];
-
-        if (curtp == irqtp) {
-                /* We're already on the irq stack, just handle it */
-                desc->handle_irq(irq, desc);
-                return;
-        }
-
-        saved_sp_limit = current->thread.ksp_limit;
-
-        irqtp->task = curtp->task;
-        irqtp->flags = 0;
-
-        /* Copy the softirq bits in preempt_count so that the
-         * softirq checks work in the hardirq context. */
-        irqtp->preempt_count = (irqtp->preempt_count & ~SOFTIRQ_MASK) |
-                               (curtp->preempt_count & SOFTIRQ_MASK);
-
-        current->thread.ksp_limit = (unsigned long)irqtp +
-                _ALIGN_UP(sizeof(struct thread_info), 16);
-
-        call_handle_irq(irq, desc, irqtp, desc->handle_irq);
-        current->thread.ksp_limit = saved_sp_limit;
-        irqtp->task = NULL;
-
-        /* Set any flag that may have been set on the
-         * alternate stack
-         */
-        if (irqtp->flags)
-                set_bits(irqtp->flags, &curtp->flags);
-}
-
 static inline void check_stack_overflow(void)
 {
 #ifdef CONFIG_DEBUG_STACKOVERFLOW
@@ -501,9 +457,9 @@ static inline void check_stack_overflow(void)
 #endif
 }
 
-void do_IRQ(struct pt_regs *regs)
+void __do_irq(struct pt_regs *regs)
 {
-        struct pt_regs *old_regs = set_irq_regs(regs);
+        struct irq_desc *desc;
         unsigned int irq;
 
         irq_enter();
@@ -519,18 +475,64 @@ void do_IRQ(struct pt_regs *regs)
          */
         irq = ppc_md.get_irq();
 
-        /* We can hard enable interrupts now */
+        /* We can hard enable interrupts now to allow perf interrupts */
         may_hard_irq_enable();
 
         /* And finally process it */
-        if (irq != NO_IRQ)
-                handle_one_irq(irq);
-        else
+        if (unlikely(irq == NO_IRQ))
                 __get_cpu_var(irq_stat).spurious_irqs++;
+        else {
+                desc = irq_to_desc(irq);
+                if (likely(desc))
+                        desc->handle_irq(irq, desc);
+        }
 
         trace_irq_exit(regs);
 
         irq_exit();
+}
+
+void do_IRQ(struct pt_regs *regs)
+{
+        struct pt_regs *old_regs = set_irq_regs(regs);
+        struct thread_info *curtp, *irqtp;
+        unsigned long saved_sp_limit;
+
+        /* Switch to the irq stack to handle this */
+        curtp = current_thread_info();
+        irqtp = hardirq_ctx[raw_smp_processor_id()];
+
+        /* Already there ? */
+        if (unlikely(curtp == irqtp)) {
+                __do_irq(regs);
+                set_irq_regs(old_regs);
+                return;
+        }
+
+        /* Adjust the stack limit */
+        saved_sp_limit = current->thread.ksp_limit;
+        current->thread.ksp_limit = (unsigned long)irqtp +
+                _ALIGN_UP(sizeof(struct thread_info), 16);
+
+
+        /* Prepare the thread_info in the irq stack */
+        irqtp->task = curtp->task;
+        irqtp->flags = 0;
+
+        /* Copy the preempt_count so that the [soft]irq checks work. */
+        irqtp->preempt_count = curtp->preempt_count;
+
+        /* Switch stack and call */
+        call_do_irq(regs, irqtp);
+
+        /* Restore stack limit */
+        current->thread.ksp_limit = saved_sp_limit;
+        irqtp->task = NULL;
+
+        /* Copy back updates to the thread_info */
+        if (irqtp->flags)
+                set_bits(irqtp->flags, &curtp->flags);
+
         set_irq_regs(old_regs);
 }
 
@@ -592,12 +594,10 @@ void irq_ctx_init(void)
                 memset((void *)softirq_ctx[i], 0, THREAD_SIZE);
                 tp = softirq_ctx[i];
                 tp->cpu = i;
-                tp->preempt_count = 0;
 
                 memset((void *)hardirq_ctx[i], 0, THREAD_SIZE);
                 tp = hardirq_ctx[i];
                 tp->cpu = i;
-                tp->preempt_count = HARDIRQ_OFFSET;
         }
 }
 
diff --git a/arch/powerpc/kernel/misc_32.S b/arch/powerpc/kernel/misc_32.S
index 777d999f563b..7da3882a3622 100644
--- a/arch/powerpc/kernel/misc_32.S
+++ b/arch/powerpc/kernel/misc_32.S
@@ -47,13 +47,12 @@ _GLOBAL(call_do_softirq)
         mtlr    r0
         blr
 
-_GLOBAL(call_handle_irq)
+_GLOBAL(call_do_irq)
         mflr    r0
         stw     r0,4(r1)
-        mtctr   r6
-        stwu    r1,THREAD_SIZE-STACK_FRAME_OVERHEAD(r5)
-        mr      r1,r5
-        bctrl
+        stwu    r1,THREAD_SIZE-STACK_FRAME_OVERHEAD(r4)
+        mr      r1,r4
+        bl      __do_irq
         lwz     r1,0(r1)
         lwz     r0,4(r1)
         mtlr    r0
diff --git a/arch/powerpc/kernel/misc_64.S b/arch/powerpc/kernel/misc_64.S
index 971d7e78aff2..e59caf874d05 100644
--- a/arch/powerpc/kernel/misc_64.S
+++ b/arch/powerpc/kernel/misc_64.S
@@ -40,14 +40,12 @@ _GLOBAL(call_do_softirq)
         mtlr    r0
         blr
 
-_GLOBAL(call_handle_irq)
-        ld      r8,0(r6)
+_GLOBAL(call_do_irq)
         mflr    r0
         std     r0,16(r1)
-        mtctr   r8
-        stdu    r1,THREAD_SIZE-STACK_FRAME_OVERHEAD(r5)
-        mr      r1,r5
-        bctrl
+        stdu    r1,THREAD_SIZE-STACK_FRAME_OVERHEAD(r4)
+        mr      r1,r4
+        bl      .__do_irq
         ld      r1,0(r1)
         ld      r0,16(r1)
         mtlr    r0