Revert "mm: oom_kill: reap memory of a task that receives SIGKILL"

This reverts commit 97bf2fb571.

Reason to revert: The changes introduced in this commit are
causing an undesirable SELinux denial as a side-effect and
we do not enable the functionality that this commit adds.
Reverting the commit fixes the SELinux denial bug.

Bug: 152624411
Test: boot
Signed-off-by: Martin Liu <liumartin@google.com>
Change-Id: I149b66e6fa0e90e691436e1a83261ff1de233669
Signed-off-by: UtsavBalar1231 <utsavbalar1231@gmail.com>

Documentation/sysctl/vm.txt

@@ -51,7 +51,6 @@ Currently, these files are in /proc/sys/vm:
 - nr_trim_pages         (only if CONFIG_MMU=n)
 - numa_zonelist_order
 - oom_dump_tasks
-- reap_mem_on_sigkill
 - oom_kill_allocating_task
 - overcommit_kbytes
 - overcommit_memory
@@ -656,24 +655,6 @@ The default value is 1 (enabled).
 
 ==============================================================
 
-reap_mem_on_sigkill
-
-This enables or disables the memory reaping for a SIGKILL received
-process and that the sending process must have the CAP_KILL capabilities.
-
-If this is set to 1, when a process receives SIGKILL from a process
-that has the capability, CAP_KILL, the process is added into the oom_reaper
-queue which can be picked up by the oom_reaper thread to reap the memory of
-that process. This reaps for the process which received SIGKILL through
-either sys_kill from user or kill_pid from kernel.
-
-If this is set to 0, we are not reaping memory of a SIGKILL, sent through
-either sys_kill from user or kill_pid from kernel, received process.
-
-The default value is 0 (disabled).
-
-==============================================================
-
 oom_kill_allocating_task
 
 This enables or disables killing the OOM-triggering task in

include/linux/oom.h

@@ -120,8 +120,4 @@ extern void dump_tasks(struct mem_cgroup *memcg,
 extern int sysctl_oom_dump_tasks;
 extern int sysctl_oom_kill_allocating_task;
 extern int sysctl_panic_on_oom;
-extern int sysctl_reap_mem_on_sigkill;
-
-/* calls for LMK reaper */
-extern void add_to_oom_reaper(struct task_struct *p);
 #endif /* _INCLUDE_LINUX_OOM_H */

kernel/signal.c

@@ -43,8 +43,6 @@
 #include <linux/compiler.h>
 #include <linux/posix-timers.h>
 #include <linux/livepatch.h>
-#include <linux/oom.h>
-#include <linux/capability.h>
 #include <linux/cgroup.h>
 
 #define CREATE_TRACE_POINTS
@@ -1387,11 +1385,8 @@ int group_send_sig_info(int sig, struct siginfo *info, struct task_struct *p,
 	ret = check_kill_permission(sig, info, p);
 	rcu_read_unlock();
 
-	if (!ret && sig) {
+	if (!ret && sig)
 		ret = do_send_sig_info(sig, info, p, type);
-		if (capable(CAP_KILL) && sig == SIGKILL)
-			add_to_oom_reaper(p);
-	}
 
 	return ret;
 }

kernel/sysctl.c

@@ -1663,13 +1663,6 @@ static struct ctl_table vm_table[] = {
 		.mode		= 0644,
 		.proc_handler	= proc_dointvec,
 	},
-	{
-		.procname       = "reap_mem_on_sigkill",
-		.data           = &sysctl_reap_mem_on_sigkill,
-		.maxlen         = sizeof(sysctl_reap_mem_on_sigkill),
-		.mode           = 0644,
-		.proc_handler   = proc_dointvec,
-	},
 	{
 		.procname	= "overcommit_ratio",
 		.data		= &sysctl_overcommit_ratio,

mm/oom_kill.c

@@ -54,7 +54,6 @@
 int sysctl_panic_on_oom;
 int sysctl_oom_kill_allocating_task;
 int sysctl_oom_dump_tasks = 1;
-int sysctl_reap_mem_on_sigkill;
 
 /*
  * Serializes oom killer invocations (out_of_memory()) from all contexts to
@@ -642,21 +641,13 @@ static int oom_reaper(void *unused)
 
 static void wake_oom_reaper(struct task_struct *tsk)
 {
-	/*
-	 * Move the lock here to avoid scenario of queuing
-	 * the same task by both OOM killer and any other SIGKILL
-	 * path.
-	 */
-	spin_lock(&oom_reaper_lock);
-
 	/* mm is already queued? */
-	if (test_and_set_bit(MMF_OOM_REAP_QUEUED, &tsk->signal->oom_mm->flags)) {
+	if (test_and_set_bit(MMF_OOM_REAP_QUEUED, &tsk->signal->oom_mm->flags))
-		spin_unlock(&oom_reaper_lock);
 		return;
-	}
 
 	get_task_struct(tsk);
 
+	spin_lock(&oom_reaper_lock);
 	tsk->oom_reaper_list = oom_reaper_list;
 	oom_reaper_list = tsk;
 	spin_unlock(&oom_reaper_lock);
@@ -676,16 +667,6 @@ static inline void wake_oom_reaper(struct task_struct *tsk)
 }
 #endif /* CONFIG_MMU */
 
-static void __mark_oom_victim(struct task_struct *tsk)
-{
-	struct mm_struct *mm = tsk->mm;
-
-	if (!cmpxchg(&tsk->signal->oom_mm, NULL, mm)) {
-		mmgrab(tsk->signal->oom_mm);
-		set_bit(MMF_OOM_VICTIM, &mm->flags);
-	}
-}
-
 /**
  * mark_oom_victim - mark the given task as OOM victim
  * @tsk: task to mark
@@ -698,13 +679,18 @@ static void __mark_oom_victim(struct task_struct *tsk)
  */
 static void mark_oom_victim(struct task_struct *tsk)
 {
+	struct mm_struct *mm = tsk->mm;
+
 	WARN_ON(oom_killer_disabled);
 	/* OOM killer might race with memcg OOM */
 	if (test_and_set_tsk_thread_flag(tsk, TIF_MEMDIE))
 		return;
 
 	/* oom_mm is bound to the signal struct life time. */
-	__mark_oom_victim(tsk);
+	if (!cmpxchg(&tsk->signal->oom_mm, NULL, mm)) {
+		mmgrab(tsk->signal->oom_mm);
+		set_bit(MMF_OOM_VICTIM, &mm->flags);
+	}
 
 	/*
 	 * Make sure that the task is woken up from uninterruptible sleep
@@ -1179,21 +1165,3 @@ void pagefault_out_of_memory(void)
 	if (__ratelimit(&pfoom_rs))
 		pr_warn("Huh VM_FAULT_OOM leaked out to the #PF handler. Retrying PF\n");
 }
-
-void add_to_oom_reaper(struct task_struct *p)
-{
-	if (!sysctl_reap_mem_on_sigkill)
-		return;
-
-	p = find_lock_task_mm(p);
-	if (!p)
-		return;
-
-	get_task_struct(p);
-	if (task_will_free_mem(p)) {
-		__mark_oom_victim(p);
-		wake_oom_reaper(p);
-	}
-	task_unlock(p);
-	put_task_struct(p);
-}