Blackfin: fix up mm locking in address dumping

The locking code in the address dumper needs to grab the mm's mmap_sem
so that other CPUs do not get an inconsistent view.  On UP systems this
really wasn't a problem, but it is easy to trigger a race on SMP systems
when another CPU removes a mapping.

Signed-off-by: Graf Yang <graf.yang@analog.com>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>

1 files changed, 13 insertions, 1 deletions

diff --git a/arch/blackfin/kernel/traps.c b/arch/blackfin/kernel/traps.c
index 870d74b1b407..85766805b03a 100644
--- a/arch/blackfin/kernel/traps.c
+++ b/arch/blackfin/kernel/traps.c
@@ -138,6 +138,12 @@ static void decode_address(char *buf, unsigned long address)
                 if (!mm)
                         continue;
 
+                if (!down_read_trylock(&mm->mmap_sem)) {
+                        if (!in_atomic)
+                                mmput(mm);
+                        continue;
+                }
+
                 for (n = rb_first(&mm->mm_rb); n; n = rb_next(n)) {
                         struct vm_area_struct *vma;
 
@@ -177,6 +183,7 @@ static void decode_address(char *buf, unsigned long address)
                                         sprintf(buf, "[ %s vma:0x%lx-0x%lx]",
                                                 name, vma->vm_start, vma->vm_end);
 
+                                up_read(&mm->mmap_sem);
                                 if (!in_atomic)
                                         mmput(mm);
 
@@ -186,11 +193,16 @@ static void decode_address(char *buf, unsigned long address)
                                 goto done;
                         }
                 }
+
+                up_read(&mm->mmap_sem);
                 if (!in_atomic)
                         mmput(mm);
         }
 
-        /* we were unable to find this address anywhere */
+        /*
+         * we were unable to find this address anywhere,
+         * or some MMs were skipped because they were in use.
+         */
         sprintf(buf, "/* kernel dynamic memory */");
 
 done: