sh: handle early calls to return_address() when using dwarf unwinder.

The dwarf unwinder ties in to an early initcall, but it's possible that
return_address() calls will be made prior to that. This implements some
additional error handling in to the dwarf unwinder as well as an exit
path in the return_address() case to bail out if the unwinder hasn't come
up yet.

This fixes a NULL pointer deref in early boot when mempool_alloc() blows
up on the not-yet-ready mempool via dwarf_unwind_stack().

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

2 files changed, 19 insertions, 2 deletions

diff --git a/arch/sh/kernel/dwarf.c b/arch/sh/kernel/dwarf.c
index 886d7d83ace3..49c09c7d5b77 100644
--- a/arch/sh/kernel/dwarf.c
+++ b/arch/sh/kernel/dwarf.c
@@ -49,6 +49,8 @@ static DEFINE_SPINLOCK(dwarf_fde_lock);
 
 static struct dwarf_cie *cached_cie;
 
+static unsigned int dwarf_unwinder_ready;
+
 /**
  *      dwarf_frame_alloc_reg - allocate memory for a DWARF register
  *      @frame: the DWARF frame whose list of registers we insert on
@@ -582,6 +584,13 @@ struct dwarf_frame *dwarf_unwind_stack(unsigned long pc,
         unsigned long addr;
 
         /*
+         * If we've been called in to before initialization has
+         * completed, bail out immediately.
+         */
+        if (!dwarf_unwinder_ready)
+                return NULL;
+
+        /*
          * If we're starting at the top of the stack we need get the
          * contents of a physical register to get the CFA in order to
          * begin the virtual unwinding of the stack.
@@ -1167,7 +1176,7 @@ void module_dwarf_cleanup(struct module *mod)
  */
 static int __init dwarf_unwinder_init(void)
 {
-        int err;
+        int err = -ENOMEM;
 
         dwarf_frame_cachep = kmem_cache_create("dwarf_frames",
                         sizeof(struct dwarf_frame), 0,
@@ -1181,11 +1190,15 @@ static int __init dwarf_unwinder_init(void)
                                           mempool_alloc_slab,
                                           mempool_free_slab,
                                           dwarf_frame_cachep);
+        if (!dwarf_frame_pool)
+                goto out;
 
         dwarf_reg_pool = mempool_create(DWARF_REG_MIN_REQ,
                                          mempool_alloc_slab,
                                          mempool_free_slab,
                                          dwarf_reg_cachep);
+        if (!dwarf_reg_pool)
+                goto out;
 
         err = dwarf_parse_section(__start_eh_frame, __stop_eh_frame, NULL);
         if (err)
@@ -1195,11 +1208,13 @@ static int __init dwarf_unwinder_init(void)
         if (err)
                 goto out;
 
+        dwarf_unwinder_ready = 1;
+
         return 0;
 
 out:
         printk(KERN_ERR "Failed to initialise DWARF unwinder: %d\n", err);
         dwarf_unwinder_cleanup();
-        return -EINVAL;
+        return err;
 }
 early_initcall(dwarf_unwinder_init);
diff --git a/arch/sh/kernel/return_address.c b/arch/sh/kernel/return_address.c
index cbf1dd5372b2..5124aeb28c3f 100644
--- a/arch/sh/kernel/return_address.c
+++ b/arch/sh/kernel/return_address.c
@@ -24,6 +24,8 @@ void *return_address(unsigned int depth)
                 struct dwarf_frame *tmp;
 
                 tmp = dwarf_unwind_stack(ra, frame);
+                if (!tmp)
+                        return NULL;
 
                 if (frame)
                         dwarf_free_frame(frame);