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Subject[PATCH 09/10] um: Properly check all process' threads for a live mm
kill_off_processes() might miss a valid process, this is because
checking for process->mm is not enough. Process' main thread may
exit or detach its mm via use_mm(), but other threads may still
have a valid mm.

To catch this we use find_lock_task_mm(), which walks up all
threads and returns an appropriate task (with task lock held).

Suggested-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org>
---
arch/um/kernel/reboot.c | 13 +++++++------
1 file changed, 7 insertions(+), 6 deletions(-)
diff --git a/arch/um/kernel/reboot.c b/arch/um/kernel/reboot.c
index 1411f4e..3d15243 100644
--- a/arch/um/kernel/reboot.c
+++ b/arch/um/kernel/reboot.c
@@ -6,6 +6,7 @@
#include "linux/sched.h"
#include "linux/spinlock.h"
#include "linux/slab.h"
+#include "linux/oom.h"
#include "kern_util.h"
#include "os.h"
#include "skas.h"
@@ -25,13 +26,13 @@ static void kill_off_processes(void)

read_lock(&tasklist_lock);
for_each_process(p) {
- task_lock(p);
- if (!p->mm) {
- task_unlock(p);
+ struct task_struct *t;
+
+ t = find_lock_task_mm(p);
+ if (!t)
continue;
- }
- pid = p->mm->context.id.u.pid;
- task_unlock(p);
+ pid = t->mm->context.id.u.pid;
+ task_unlock(t);
os_kill_ptraced_process(pid, 1);
}
read_unlock(&tasklist_lock);
--
1.7.9.2


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