Commit dabb16f6 authored by Mandeep Singh Baines's avatar Mandeep Singh Baines Committed by Linus Torvalds
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oom: allow a non-CAP_SYS_RESOURCE proces to oom_score_adj down 



We'd like to be able to oom_score_adj a process up/down as it
enters/leaves the foreground.  Currently, it is not possible to oom_adj
down without CAP_SYS_RESOURCE.  This patch allows a task to decrease its
oom_score_adj back to the value that a CAP_SYS_RESOURCE thread set it to
or its inherited value at fork.  Assuming the thread that has forked it
has oom_score_adj of 0, each process could decrease it back from 0 upon
activation unless a CAP_SYS_RESOURCE thread elevated it to something
higher.

Alternative considered:

* a setuid binary
* a daemon with CAP_SYS_RESOURCE

Since you don't wan't all processes to be able to reduce their oom_adj, a
setuid or daemon implementation would be complex.  The alternatives also
have much higher overhead.

This patch updated from original patch based on feedback from David
Rientjes.

Signed-off-by: default avatarMandeep Singh Baines <msb@chromium.org>
Acked-by: default avatarDavid Rientjes <rientjes@google.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Ying Han <yinghan@google.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent d0a21265

Documentation/filesystems/proc.txt

+4 −0
Original line number Diff line number Diff line
@@ -1323,6 +1323,10 @@ scaled linearly with /proc/<pid>/oom_score_adj. 
Writing to /proc/<pid>/oom_score_adj or /proc/<pid>/oom_adj will change the

other with its scaled value.



The value of /proc/<pid>/oom_score_adj may be reduced no lower than the last

value set by a CAP_SYS_RESOURCE process. To reduce the value any lower

requires CAP_SYS_RESOURCE.



NOTICE: /proc/<pid>/oom_adj is deprecated and will be removed, please see

Documentation/feature-removal-schedule.txt.

fs/proc/base.c

+3 −1
Original line number Diff line number Diff line
@@ -1151,7 +1151,7 @@ static ssize_t oom_score_adj_write(struct file *file, const char __user *buf, 
		goto err_task_lock;

	}



	if (oom_score_adj < task->signal->oom_score_adj &&

	if (oom_score_adj < task->signal->oom_score_adj_min &&

			!capable(CAP_SYS_RESOURCE)) {

		err = -EACCES;

		goto err_sighand;
@@ -1164,6 +1164,8 @@ static ssize_t oom_score_adj_write(struct file *file, const char __user *buf, 
			atomic_dec(&task->mm->oom_disable_count);

	}

	task->signal->oom_score_adj = oom_score_adj;

	if (has_capability_noaudit(current, CAP_SYS_RESOURCE))

		task->signal->oom_score_adj_min = oom_score_adj;

	/*

	 * Scale /proc/pid/oom_adj appropriately ensuring that OOM_DISABLE is

	 * always attainable.

include/linux/sched.h

+2 −0
Original line number Diff line number Diff line
@@ -634,6 +634,8 @@ struct signal_struct { 


	int oom_adj;		/* OOM kill score adjustment (bit shift) */

	int oom_score_adj;	/* OOM kill score adjustment */

	int oom_score_adj_min;	/* OOM kill score adjustment minimum value.

				 * Only settable by CAP_SYS_RESOURCE. */



	struct mutex cred_guard_mutex;	/* guard against foreign influences on

					 * credential calculations

kernel/fork.c

+1 −0
Original line number Diff line number Diff line
@@ -910,6 +910,7 @@ static int copy_signal(unsigned long clone_flags, struct task_struct *tsk) 


	sig->oom_adj = current->signal->oom_adj;

	sig->oom_score_adj = current->signal->oom_score_adj;

	sig->oom_score_adj_min = current->signal->oom_score_adj_min;



	mutex_init(&sig->cred_guard_mutex);

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