powerpc/kgdb: Restore current_thread_info properly

For powerpc BooKE and e200, singlestep is handled on the critical/dbg
exception stack. This causes current_thread_info() to fail for kgdb
internal, so previously We work around this issue by copying
the thread_info from the kernel stack before calling kgdb_handle_exception,
and copying it back afterwards.

But actually we don't do this properly. We should backup current_thread_info
then restore that when exit.

Signed-off-by: Tiejun Chen <tiejun.chen@windriver.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

1 files changed, 9 insertions, 2 deletions

diff --git a/arch/powerpc/kernel/kgdb.c b/arch/powerpc/kernel/kgdb.c
index 05adb69febf..c470a40b29f 100644
--- a/arch/powerpc/kernel/kgdb.c
+++ b/arch/powerpc/kernel/kgdb.c
@@ -25,6 +25,7 @@
 #include <asm/processor.h>
 #include <asm/machdep.h>
 #include <asm/debug.h>
+#include <linux/slab.h>
 
 /*
  * This table contains the mapping between PowerPC hardware trap types, and
@@ -153,6 +154,8 @@ static int kgdb_handle_breakpoint(struct pt_regs *regs)
 static int kgdb_singlestep(struct pt_regs *regs)
 {
         struct thread_info *thread_info, *exception_thread_info;
+        struct thread_info *backup_current_thread_info = \
+                (struct thread_info *)kmalloc(sizeof(struct thread_info), GFP_KERNEL);
 
         if (user_mode(regs))
                 return 0;
@@ -170,13 +173,17 @@ static int kgdb_singlestep(struct pt_regs *regs)
         thread_info = (struct thread_info *)(regs->gpr[1] & ~(THREAD_SIZE-1));
         exception_thread_info = current_thread_info();
 
-        if (thread_info != exception_thread_info)
+        if (thread_info != exception_thread_info) {
+                /* Save the original current_thread_info. */
+                memcpy(backup_current_thread_info, exception_thread_info, sizeof *thread_info);
                 memcpy(exception_thread_info, thread_info, sizeof *thread_info);
+        }
 
         kgdb_handle_exception(0, SIGTRAP, 0, regs);
 
         if (thread_info != exception_thread_info)
-                memcpy(thread_info, exception_thread_info, sizeof *thread_info);
+                /* Restore current_thread_info lastly. */
+                memcpy(exception_thread_info, backup_current_thread_info, sizeof *thread_info);
 
         return 1;
 }