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    Subject[patch] 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 <w.landgraf@ru.ru>
    Cc: stable@vger.kernel.org
    Signed-off-by: David Rientjes <rientjes@google.com>
    ---
    drivers/staging/android/lowmemorykiller.c | 48 +++++------------------------
    1 file changed, 7 insertions(+), 41 deletions(-)

    diff --git a/drivers/staging/android/lowmemorykiller.c b/drivers/staging/android/lowmemorykiller.c
    --- 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);

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