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.voront...@linaro.org>
---
 arch/um/kernel/reboot.c |    3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/um/kernel/reboot.c b/arch/um/kernel/reboot.c
index 4d93dff..66d754c 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);
        }
 }
 
-- 
1.7.9.2

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