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staging: android/lowmemorykiller: Don't grab tasklist_lock

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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>
This commit is contained in:
Anton Vorontsov 2012-02-06 20:29:41 +04:00 committed by Greg Kroah-Hartman
parent 350a195595
commit 294b27119f
1 changed files with 4 additions and 3 deletions
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7
drivers/staging/android/lowmemorykiller.c
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@ -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;
}