[Blackfin] arch: fix bug - when we crash, current is not valid

Sometimes when we crash, current is not valid, (has been written
over), so the existing code causes a invalid read during exception
context - which is a unrecoverable double fault. This fixes this.

Signed-off-by: Robin Getz <rgetz@blackfin.uclinux.org>
Signed-off-by: Bryan Wu <cooloney@kernel.org>

1 files changed, 23 insertions, 14 deletions

diff --git a/arch/blackfin/kernel/traps.c b/arch/blackfin/kernel/traps.c
index e8e8f735c236..7557d0dce216 100644
--- a/arch/blackfin/kernel/traps.c
+++ b/arch/blackfin/kernel/traps.c
@@ -655,21 +655,30 @@ void dump_bfin_process(struct pt_regs *fp)
         else if (context & 0x8000)
                 printk(KERN_NOTICE "Kernel process context\n");
 
-        if (current->pid && current->mm) {
+        /* Because we are crashing, and pointers could be bad, we check things
+         * pretty closely before we use them
+         */
+        if (!((unsigned long)current & 0x3) && current->pid) {
                 printk(KERN_NOTICE "CURRENT PROCESS:\n");
-                printk(KERN_NOTICE "COMM=%s PID=%d\n",
-                        current->comm, current->pid);
-
-                printk(KERN_NOTICE "TEXT = 0x%p-0x%p  DATA = 0x%p-0x%p\n"
-                        KERN_NOTICE "BSS = 0x%p-0x%p   USER-STACK = 0x%p\n"
-                        KERN_NOTICE "\n",
-                        (void *)current->mm->start_code,
-                        (void *)current->mm->end_code,
-                        (void *)current->mm->start_data,
-                        (void *)current->mm->end_data,
-                        (void *)current->mm->end_data,
-                        (void *)current->mm->brk,
-                        (void *)current->mm->start_stack);
+                if (current->comm >= (char *)FIXED_CODE_START)
+                        printk(KERN_NOTICE "COMM=%s PID=%d\n",
+                                current->comm, current->pid);
+                else
+                        printk(KERN_NOTICE "COMM= invalid\n");
+
+                if (!((unsigned long)current->mm & 0x3) && (unsigned long)current->mm >= FIXED_CODE_START)
+                        printk(KERN_NOTICE  "TEXT = 0x%p-0x%p        DATA = 0x%p-0x%p\n"
+                                KERN_NOTICE " BSS = 0x%p-0x%p  USER-STACK = 0x%p\n"
+                                KERN_NOTICE "\n",
+                                (void *)current->mm->start_code,
+                                (void *)current->mm->end_code,
+                                (void *)current->mm->start_data,
+                                (void *)current->mm->end_data,
+                                (void *)current->mm->end_data,
+                                (void *)current->mm->brk,
+                                (void *)current->mm->start_stack);
+                else
+                        printk(KERN_NOTICE "invalid mm\n");
         } else
                 printk(KERN_NOTICE "\n" KERN_NOTICE
                      "No Valid process in current context\n");