staging: android: lmk: skip if killed by lmk

A task can be selected to kill when it's already exiting. Sending
signal to the task at that state won't set TIF_SIGPENDING for it.
After that, every task including threads in the exiting task itself
running into lmk will compete for the mutex, then spend some time
waiting for the exiting task to release memory or try to send signal
to the same task again.
We want the exiting task to exit as early as possible but it's slowed
down greatly by the mutex and waiting. Skip lmk if current thread
group leader is exiting and is killed by lmk. Also delegate TIF_MEMDIE
to current task.

Change-Id: Id7839b81f183165871976666bfd4e04130a00610
Signed-off-by: Yuanyuan Zhong <zyy@motorola.com>
Reviewed-on: http://gerrit.pcs.mot.com/584015
SLTApproved: Slta Waiver <sltawvr@motorola.com>
Tested-by: Jira Key <jirakey@motorola.com>
Reviewed-by: Check Patch <CHEKPACH@motorola.com>
Reviewed-by: Klocwork kwcheck <klocwork-kwcheck@sourceforge.mot.com>
Reviewed-by: Russell Knize <rknize@motorola.com>
Submit-Approved: Jira Key <jirakey@motorola.com>
staging: android: lmk: check TIF directly

When trying to fix that lmk can't kill an exiting task
(commit 895304e926352e0272964a421bd6271e47616ab3
(CR) staging: android: lmk: skip if killed by lmk),
additional check was added for the TIF_MEMDIE flag.
However the task lock has already been taken when examining
the task. The same helper function which tries to grab the
task lock again will be deadlocked.
Change to check the thread flag of thread group leader directly.

Change-Id: If1f880aaca2f053a54ab38c62f275f0a714eb5d2
Signed-off-by: Yuanyuan Zhong <zyy@motorola.com>
Reviewed-on: http://gerrit.pcs.mot.com/587751
SLTApproved: Slta Waiver <sltawvr@motorola.com>
Tested-by: Jira Key <jirakey@motorola.com>
Reviewed-by: Yi-Wei Zhao <gbjc64@motorola.com>
Submit-Approved: Jira Key <jirakey@motorola.com>