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>

diff --git a/arch/um/kernel/reboot.c b/arch/um/kernel/reboot.c
index 4d93dff6b3713e321a66f49ef160d3da4380e7a2..66d754c46e7b048492f7587fdcbe08fed2b4630d 100644 (file)
--- 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);
        }
 }