staging: android: lowmemorykiller: Don't try to kill the same pid over and over

  Under certain circumstances, a process can take awhile to
handle a sig-kill (especially if it's in a scheduler group with
a very low share ratio). When this occurs, lowmemkiller returns
to vmscan indicating the process memory has been freed - even
though the process is still waiting to die. Since the memory
hasn't actually freed, lowmemkiller is called again shortly after,
and picks the same process to die; regardless of the fact that
it has already been 'scheduled' to die and the memory has already
been reported to vmscan as having been freed.

  Solution is to check fatal_signal_pending() on the selected
task, and if it's already pending destruction return; indicating
to vmscan that no resources were freed on this pass.
Signed-off-by: NSan Mehat <san@google.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

drivers/staging/android/lowmemorykiller.c

@@ -133,6 +133,12 @@ static int lowmem_shrink(int nr_to_scan, gfp_t gfp_mask)
 			     p->pid, p->comm, oom_adj, tasksize);
 	}
 	if (selected) {
+		if (fatal_signal_pending(selected)) {
+			pr_warning("process %d is suffering a slow death\n",
+				   selected->pid);
+			read_unlock(&tasklist_lock);
+			return rem;
+		}
 		lowmem_print(1, "send sigkill to %d (%s), adj %d, size %d\n",
 			     selected->pid, selected->comm,
 			     selected_oom_adj, selected_tasksize);