staging: android: lowmemorykiller: Drop tasklist_lock usage
PATCH 3/3 staging: android: lowmemorykiller: Drop tasklist_lock usage
Instead of walking through the whole task list (where we must hold the task list lock for the whole period while we search for the victim), let's take procfs' approach of walking up the tgids (for_each_tgit() walks a pidmap, which internally grabs an rcu lock, but only while it searches for the next tgid).
Signed-off-by Anton Vorontsov <[email protected]>
--- drivers/staging/android/lowmemorykiller.c | 12 ++++++++---- 1 files changed, 8 insertions(+), 4 deletions(-)
drivers/staging/android/lowmemorykiller.c +8 -4
@@ -34,6 +34,7 @@#include <linux/mm.h> #include <linux/oom.h> #include <linux/sched.h> +#include <linux/pid.h> #include <linux/profile.h> #include <linux/notifier.h>
@@ -81,7 +82,8 @@ task_notify_func(struct notifier_block *self, unsigned long val, void *data)static int lowmem_shrink (struct shrinker *s,struct shrink_control *sc) { -struct task_struct *p; +struct pid_namespace *ns = &init_pid_ns; +struct tgid_iter iter = {};struct task_struct *selected =NULL ;int rem =0 ;int tasksize;
@@ -132,8 +134,8 @@ static int lowmem_shrink(struct shrinker *s, struct shrink_control *sc) } selected_oom_adj = min_adj; -read_lock (&tasklist_lock); -for_each_process (p) { +for_each_tgid (ns, iter) { +struct task_struct *p = iter.task;struct mm_struct *mm;struct signal_struct *sig;int oom_adj;
@@ -160,7 +162,9 @@ static int lowmem_shrink(struct shrinker *s, struct shrink_control *sc)if (oom_adj == selected_oom_adj && tasksize <= selected_tasksize)continue ; +put_task_struct (selected); } +get_task_struct (p); selected = p; selected_tasksize = tasksize; selected_oom_adj = oom_adj;
@@ -181,11 +185,11 @@ static int lowmem_shrink(struct shrinker *s, struct shrink_control *sc)task_handoff_register (&task_nb);#endif force_sig (SIGKILL , selected); +put_task_struct (selected); 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);return rem; }
Signature · 1 line
1.7.7
drivers/staging/android/lowmemorykiller.c static int lowmem_shrink(struct shrinker *s, struct shrink_control *sc) · line 137
Quoted 8 lines · Anton Vorontsov
drivers/staging/android/lowmemorykiller.c +1
-2@@ -132,8 +134,8 @@ static int lowmem_shrink(struct shrinker *s, struct shrink_control *sc) } selected_oom_adj = min_adj; -read_lock (&tasklist_lock); -for_each_process (p) { +for_each_tgid (ns, iter) {
This makes force_sig() below unsafe, it can race with the exiting task.
Oleg.