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Subject[ 63/78] android, lowmemorykiller: remove task handoff notifier
3.3-stable review patch.  If anyone has any objections, please let me know.

------------------

From: David Rientjes <rientjes@google.com>

commit 83dbbdbb38666e20a75fad2294cf1df77c52f121 upstream.

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>
Signed-off-by: David Rientjes <rientjes@google.com>
Acked-by: Colin Cross <ccross@android.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/staging/android/lowmemorykiller.c | 47 +++---------------------------
1 file changed, 6 insertions(+), 41 deletions(-)

--- a/drivers/staging/android/lowmemorykiller.c
+++ b/drivers/staging/android/lowmemorykiller.c
@@ -53,7 +53,6 @@ static size_t 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...) \
@@ -62,24 +61,6 @@ static unsigned long lowmem_deathpending
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 *p;
@@ -95,19 +76,6 @@ static int lowmem_shrink(struct shrinker
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)
@@ -140,6 +108,11 @@ static int lowmem_shrink(struct shrinker
struct signal_struct *sig;
int oom_adj;

+ if (test_tsk_thread_flag(p, TIF_MEMDIE) &&
+ time_before_eq(jiffies, lowmem_deathpending_timeout)) {
+ read_unlock(&tasklist_lock);
+ return 0;
+ }
task_lock(p);
mm = p->mm;
sig = p->signal;
@@ -173,15 +146,9 @@ static int lowmem_shrink(struct shrinker
lowmem_print(1, "send sigkill to %d (%s), adj %d, size %d\n",
selected->pid, selected->comm,
selected_oom_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
force_sig(SIGKILL, selected);
+ set_tsk_thread_flag(selected, TIF_MEMDIE);
rem -= selected_tasksize;
}
lowmem_print(4, "lowmem_shrink %lu, %x, return %d\n",
@@ -197,7 +164,6 @@ static struct shrinker lowmem_shrinker =

static int __init lowmem_init(void)
{
- task_handoff_register(&task_nb);
register_shrinker(&lowmem_shrinker);
return 0;
}
@@ -205,7 +171,6 @@ 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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