um: should hold tasklist_lock while traversing processes

Traversing the tasks requires holding tasklist_lock, otherwise it is
unsafe.

p.s.  However, I'm not sure that calling os_kill_ptraced_process() in the
atomic context is correct.  It seem to work, but please take a closer
look.

Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org>
Cc: Richard Weinberger <richard@nod.at>
Cc: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 3 insertions, 0 deletions

diff --git a/arch/um/kernel/reboot.c b/arch/um/kernel/reboot.c
index 4d93dff6b371..66d754c46e7b 100644
--- a/arch/um/kernel/reboot.c
+++ b/arch/um/kernel/reboot.c
@@ -4,6 +4,7 @@
  */
 
 #include "linux/sched.h"
+#include "linux/spinlock.h"
 #include "linux/slab.h"
 #include "kern_util.h"
 #include "os.h"
@@ -22,6 +23,7 @@ static void kill_off_processes(void)
                 struct task_struct *p;
                 int pid;
 
+                read_lock(&tasklist_lock);
                 for_each_process(p) {
                         if (p->mm == NULL)
                                 continue;
@@ -29,6 +31,7 @@ static void kill_off_processes(void)
                         pid = p->mm->context.id.u.pid;
                         os_kill_ptraced_process(pid, 1);
                 }
+                read_unlock(&tasklist_lock);
         }
 }