staging: android/lowmemorykiller: Don't grab tasklist_lock (294b2711) · Commits · e / devices / android_kernel_teracube_emerald

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> Reviewed-by:

Oleg Nesterov <oleg@redhat.com> Signed-off-by:

Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/android/lowmemorykiller.c

+4 −3

Original line number	Diff line number	Diff line
		@@ -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;
		}