sh: Decouple 4k and soft/hardirq stacks.

While using separate IRQ stacks can cut down on stack consumption,
many users can also use 4k stacks directly without the additional
need of separate stacks for soft and hardirqs.

With this split, we support the same rationale for 4KSTACKS as
m68knommu, with the IRQSTACKS abstraction as per ppc64.

Signed-off-by: Paul Mundt <lethal@linux-sh.org>

2 files changed, 12 insertions, 4 deletions

diff --git a/arch/sh/Kconfig.debug b/arch/sh/Kconfig.debug
index b507b501f0cf..ab2f9f3c354c 100644
--- a/arch/sh/Kconfig.debug
+++ b/arch/sh/Kconfig.debug
@@ -86,6 +86,14 @@ config 4KSTACKS
           on the VM subsystem for higher order allocations. This option
           will also use IRQ stacks to compensate for the reduced stackspace.
 
+config IRQSTACKS
+        bool "Use separate kernel stacks when processing interrupts"
+        depends on DEBUG_KERNEL
+        help
+          If you say Y here the kernel will use separate kernel stacks
+          for handling hard and soft interrupts.  This can help avoid
+          overflowing the process kernel stacks.
+
 config SH_KGDB
         bool "Include KGDB kernel debugger"
         select FRAME_POINTER
diff --git a/arch/sh/kernel/irq.c b/arch/sh/kernel/irq.c
index 4b49d03ffbd2..348da194ec99 100644
--- a/arch/sh/kernel/irq.c
+++ b/arch/sh/kernel/irq.c
@@ -69,7 +69,7 @@ unlock:
 }
 #endif
 
-#ifdef CONFIG_4KSTACKS
+#ifdef CONFIG_IRQSTACKS
 /*
  * per-CPU IRQ handling contexts (thread information and stack)
  */
@@ -85,7 +85,7 @@ static union irq_ctx *softirq_ctx[NR_CPUS] __read_mostly;
 asmlinkage int do_IRQ(unsigned int irq, struct pt_regs *regs)
 {
         struct pt_regs *old_regs = set_irq_regs(regs);
-#ifdef CONFIG_4KSTACKS
+#ifdef CONFIG_IRQSTACKS
         union irq_ctx *curctx, *irqctx;
 #endif
 
@@ -109,7 +109,7 @@ asmlinkage int do_IRQ(unsigned int irq, struct pt_regs *regs)
 
         irq = irq_demux(evt2irq(irq));
 
-#ifdef CONFIG_4KSTACKS
+#ifdef CONFIG_IRQSTACKS
         curctx = (union irq_ctx *)current_thread_info();
         irqctx = hardirq_ctx[smp_processor_id()];
 
@@ -157,7 +157,7 @@ asmlinkage int do_IRQ(unsigned int irq, struct pt_regs *regs)
         return 1;
 }
 
-#ifdef CONFIG_4KSTACKS
+#ifdef CONFIG_IRQSTACKS
 static char softirq_stack[NR_CPUS * THREAD_SIZE]
                 __attribute__((__section__(".bss.page_aligned")));