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    Subject[PATCH 3/6] staging: android/lowmemorykiller: Don't grab tasklist_lock
    Grabbing tasklist_lock has its disadvantages, i.e. it blocks
    process creation and destruction. If there are lots of processes,
    blocking doesn't sound as a great idea.

    For LMK, it is sufficient to surround tasks list traverse with
    rcu_read_{,un}lock().

    From now on using force_sig() is not safe, as it can race with an
    already exiting task, so we use send_sig() now. As a downside, it
    won't kill PID namespace init processes, but that's not what we
    want anyway.

    Suggested-by: Oleg Nesterov <oleg@redhat.com>
    Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org>
    ---
    drivers/staging/android/lowmemorykiller.c | 7 ++++---
    1 files changed, 4 insertions(+), 3 deletions(-)

    diff --git a/drivers/staging/android/lowmemorykiller.c b/drivers/staging/android/lowmemorykiller.c
    index 2d8d2b7..63da844 100644
    --- a/drivers/staging/android/lowmemorykiller.c
    +++ b/drivers/staging/android/lowmemorykiller.c
    @@ -34,6 +34,7 @@
    #include <linux/mm.h>
    #include <linux/oom.h>
    #include <linux/sched.h>
    +#include <linux/rcupdate.h>
    #include <linux/profile.h>
    #include <linux/notifier.h>

    @@ -132,7 +133,7 @@ static int lowmem_shrink(struct shrinker *s, struct shrink_control *sc)
    }
    selected_oom_adj = min_adj;

    - read_lock(&tasklist_lock);
    + rcu_read_lock();
    for_each_process(p) {
    struct mm_struct *mm;
    struct signal_struct *sig;
    @@ -180,12 +181,12 @@ static int lowmem_shrink(struct shrinker *s, struct shrink_control *sc)
    lowmem_deathpending = selected;
    task_handoff_register(&task_nb);
    #endif
    - force_sig(SIGKILL, selected);
    + send_sig(SIGKILL, selected, 0);
    rem -= selected_tasksize;
    }
    lowmem_print(4, "lowmem_shrink %lu, %x, return %d\n",
    sc->nr_to_scan, sc->gfp_mask, rem);
    - read_unlock(&tasklist_lock);
    + rcu_read_unlock();
    return rem;
    }

    --
    1.7.7.6


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