android, lowmemorykiller: remove task handoff notifier

The task handoff notifier leaks task_struct since it never gets freed
after the callback returns NOTIFY_OK, which means it is responsible for
doing so.

It turns out the lowmemorykiller actually doesn't need this notifier at
all.  It's used to prevent unnecessary killing by waiting for a thread
to exit as a result of lowmem_shrink(), however, it's possible to do
this in the same way the kernel oom killer works by setting TIF_MEMDIE
and avoid killing if we're still waiting for it to exit.

The kernel oom killer will already automatically set TIF_MEMDIE for
threads that are attempting to allocate memory that have a fatal signal.
The thread selected by lowmem_shrink() will have such a signal after the
lowmemorykiller sends it a SIGKILL, so this won't result in an
unnecessary use of memory reserves for the thread to exit.

This has the added benefit that we don't have to rely on
CONFIG_PROFILING to prevent needlessly killing tasks.

Reported-by: Werner Landgraf <w.landgraf@ru.ru>
Cc: stable@vger.kernel.org
Signed-off-by: David Rientjes <rientjes@google.com>
Acked-by: Colin Cross <ccross@android.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/drivers/staging/android/lowmemorykiller.c b/drivers/staging/android/lowmemorykiller.c
index 052b43e..b91e4bc 100644 (file)
--- a/drivers/staging/android/lowmemorykiller.c
+++ b/drivers/staging/android/lowmemorykiller.c
@@ -55,7 +55,6 @@ static int lowmem_minfree[6] = {
 };
 static int lowmem_minfree_size = 4;
 
-static struct task_struct *lowmem_deathpending;
 static unsigned long lowmem_deathpending_timeout;
 
 #define lowmem_print(level, x...)                      \
@@ -64,24 +63,6 @@ static unsigned long lowmem_deathpending_timeout;
                        printk(x);                      \
        } while (0)
 
-static int
-task_notify_func(struct notifier_block *self, unsigned long val, void *data);
-
-static struct notifier_block task_nb = {
-       .notifier_call  = task_notify_func,
-};
-
-static int
-task_notify_func(struct notifier_block *self, unsigned long val, void *data)
-{
-       struct task_struct *task = data;
-
-       if (task == lowmem_deathpending)
-               lowmem_deathpending = NULL;
-
-       return NOTIFY_OK;
-}
-
 static int lowmem_shrink(struct shrinker *s, struct shrink_control *sc)
 {
        struct task_struct *tsk;
@@ -97,19 +78,6 @@ static int lowmem_shrink(struct shrinker *s, struct shrink_control *sc)
        int other_file = global_page_state(NR_FILE_PAGES) -
                                                global_page_state(NR_SHMEM);
 
-       /*
-        * If we already have a death outstanding, then
-        * bail out right away; indicating to vmscan
-        * that we have nothing further to offer on
-        * this pass.
-        *
-        * Note: Currently you need CONFIG_PROFILING
-        * for this to work correctly.
-        */
-       if (lowmem_deathpending &&
-           time_before_eq(jiffies, lowmem_deathpending_timeout))
-               return 0;
-
        if (lowmem_adj_size < array_size)
                array_size = lowmem_adj_size;
        if (lowmem_minfree_size < array_size)
@@ -148,6 +116,12 @@ static int lowmem_shrink(struct shrinker *s, struct shrink_control *sc)
                if (!p)
                        continue;
 
+               if (test_tsk_thread_flag(p, TIF_MEMDIE) &&
+                   time_before_eq(jiffies, lowmem_deathpending_timeout)) {
+                       task_unlock(p);
+                       rcu_read_unlock();
+                       return 0;
+               }
                oom_score_adj = p->signal->oom_score_adj;
                if (oom_score_adj < min_score_adj) {
                        task_unlock(p);
@@ -174,15 +148,9 @@ static int lowmem_shrink(struct shrinker *s, struct shrink_control *sc)
                lowmem_print(1, "send sigkill to %d (%s), adj %d, size %d\n",
                             selected->pid, selected->comm,
                             selected_oom_score_adj, selected_tasksize);
-               /*
-                * If CONFIG_PROFILING is off, then we don't want to stall
-                * the killer by setting lowmem_deathpending.
-                */
-#ifdef CONFIG_PROFILING
-               lowmem_deathpending = selected;
                lowmem_deathpending_timeout = jiffies + HZ;
-#endif
                send_sig(SIGKILL, selected, 0);
+               set_tsk_thread_flag(selected, TIF_MEMDIE);
                rem -= selected_tasksize;
        }
        lowmem_print(4, "lowmem_shrink %lu, %x, return %d\n",
@@ -198,7 +166,6 @@ static struct shrinker lowmem_shrinker = {
 
 static int __init lowmem_init(void)
 {
-       task_handoff_register(&task_nb);
        register_shrinker(&lowmem_shrinker);
        return 0;
 }
@@ -206,7 +173,6 @@ static int __init lowmem_init(void)
 static void __exit lowmem_exit(void)
 {
        unregister_shrinker(&lowmem_shrinker);
-       task_handoff_unregister(&task_nb);
 }
 
 module_param_named(cost, lowmem_shrinker.seeks, int, S_IRUGO | S_IWUSR);