The patch titled
oom: allow a non-CAP_SYS_RESOURCE proces to oom_score_adj down
has been added to the -mm tree. Its filename is
oom-allow-a-non-cap_sys_resource-proces-to-oom_score_adj-down.patch
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Subject: oom: allow a non-CAP_SYS_RESOURCE proces to oom_score_adj down
From: Mandeep Singh Baines <msb@xxxxxxxxxxxx>
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: Mandeep Singh Baines <msb@xxxxxxxxxxxx>
Acked-by: David Rientjes <rientjes@xxxxxxxxxx>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
Cc: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Cc: Ying Han <yinghan@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
Documentation/filesystems/proc.txt | 4 ++++
fs/proc/base.c | 4 +++-
include/linux/sched.h | 2 ++
kernel/fork.c | 1 +
4 files changed, 10 insertions(+), 1 deletion(-)
diff -puN Documentation/filesystems/proc.txt~oom-allow-a-non-cap_sys_resource-proces-to-oom_score_adj-down Documentation/filesystems/proc.txt
--- a/Documentation/filesystems/proc.txt~oom-allow-a-non-cap_sys_resource-proces-to-oom_score_adj-down
+++ a/Documentation/filesystems/proc.txt
@@ -1323,6 +1323,10 @@ scaled linearly with /proc/<pid>/oom_sco
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.
diff -puN fs/proc/base.c~oom-allow-a-non-cap_sys_resource-proces-to-oom_score_adj-down fs/proc/base.c
--- a/fs/proc/base.c~oom-allow-a-non-cap_sys_resource-proces-to-oom_score_adj-down
+++ a/fs/proc/base.c
@@ -1164,7 +1164,7 @@ static ssize_t oom_score_adj_write(struc
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;
@@ -1177,6 +1177,8 @@ static ssize_t oom_score_adj_write(struc
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.
diff -puN include/linux/sched.h~oom-allow-a-non-cap_sys_resource-proces-to-oom_score_adj-down include/linux/sched.h
--- a/include/linux/sched.h~oom-allow-a-non-cap_sys_resource-proces-to-oom_score_adj-down
+++ a/include/linux/sched.h
@@ -626,6 +626,8 @@ 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
diff -puN kernel/fork.c~oom-allow-a-non-cap_sys_resource-proces-to-oom_score_adj-down kernel/fork.c
--- a/kernel/fork.c~oom-allow-a-non-cap_sys_resource-proces-to-oom_score_adj-down
+++ a/kernel/fork.c
@@ -907,6 +907,7 @@ static int copy_signal(unsigned long clo
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);
_
Patches currently in -mm which might be from msb@xxxxxxxxxxxx are
oom-allow-a-non-cap_sys_resource-proces-to-oom_score_adj-down.patch
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