From: Michal Hocko <mhocko@kernel.org>
To: <linux-mm@kvack.org>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>,
David Rientjes <rientjes@google.com>,
Oleg Nesterov <oleg@redhat.com>,
Vladimir Davydov <vdavydov@parallels.com>,
Andrew Morton <akpm@linux-foundation.org>,
LKML <linux-kernel@vger.kernel.org>,
Michal Hocko <mhocko@suse.com>
Subject: [PATCH 02/10] proc, oom: drop bogus sighand lock
Date: Mon, 20 Jun 2016 14:43:40 +0200 [thread overview]
Message-ID: <1466426628-15074-3-git-send-email-mhocko@kernel.org> (raw)
In-Reply-To: <1466426628-15074-1-git-send-email-mhocko@kernel.org>
From: Michal Hocko <mhocko@suse.com>
Oleg has pointed out that can simplify both oom_adj_{read,write}
and oom_score_adj_{read,write} even further and drop the sighand
lock. The main purpose of the lock was to protect p->signal from
going away but this will not happen since ea6d290ca34c ("signals:
make task_struct->signal immutable/refcountable").
The other role of the lock was to synchronize different writers,
especially those with CAP_SYS_RESOURCE. Introduce a mutex for this
purpose. Later patches will need this lock anyway.
Suggested-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Michal Hocko <mhocko@suse.com>
---
fs/proc/base.c | 51 +++++++++++++++++----------------------------------
1 file changed, 17 insertions(+), 34 deletions(-)
diff --git a/fs/proc/base.c b/fs/proc/base.c
index a6014e45c516..968d5ea06e62 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -1024,23 +1024,21 @@ static ssize_t oom_adj_read(struct file *file, char __user *buf, size_t count,
char buffer[PROC_NUMBUF];
int oom_adj = OOM_ADJUST_MIN;
size_t len;
- unsigned long flags;
if (!task)
return -ESRCH;
- if (lock_task_sighand(task, &flags)) {
- if (task->signal->oom_score_adj == OOM_SCORE_ADJ_MAX)
- oom_adj = OOM_ADJUST_MAX;
- else
- oom_adj = (task->signal->oom_score_adj * -OOM_DISABLE) /
- OOM_SCORE_ADJ_MAX;
- unlock_task_sighand(task, &flags);
- }
+ if (task->signal->oom_score_adj == OOM_SCORE_ADJ_MAX)
+ oom_adj = OOM_ADJUST_MAX;
+ else
+ oom_adj = (task->signal->oom_score_adj * -OOM_DISABLE) /
+ OOM_SCORE_ADJ_MAX;
put_task_struct(task);
len = snprintf(buffer, sizeof(buffer), "%d\n", oom_adj);
return simple_read_from_buffer(buf, count, ppos, buffer, len);
}
+static DEFINE_MUTEX(oom_adj_mutex);
+
/*
* /proc/pid/oom_adj exists solely for backwards compatibility with previous
* kernels. The effective policy is defined by oom_score_adj, which has a
@@ -1057,7 +1055,6 @@ static ssize_t oom_adj_write(struct file *file, const char __user *buf,
struct task_struct *task;
char buffer[PROC_NUMBUF];
int oom_adj;
- unsigned long flags;
int err;
memset(buffer, 0, sizeof(buffer));
@@ -1083,11 +1080,6 @@ static ssize_t oom_adj_write(struct file *file, const char __user *buf,
goto out;
}
- if (!lock_task_sighand(task, &flags)) {
- err = -ESRCH;
- goto err_put_task;
- }
-
/*
* Scale /proc/pid/oom_score_adj appropriately ensuring that a maximum
* value is always attainable.
@@ -1097,10 +1089,11 @@ static ssize_t oom_adj_write(struct file *file, const char __user *buf,
else
oom_adj = (oom_adj * OOM_SCORE_ADJ_MAX) / -OOM_DISABLE;
+ mutex_lock(&oom_adj_mutex);
if (oom_adj < task->signal->oom_score_adj &&
!capable(CAP_SYS_RESOURCE)) {
err = -EACCES;
- goto err_sighand;
+ goto err_unlock;
}
/*
@@ -1113,9 +1106,8 @@ static ssize_t oom_adj_write(struct file *file, const char __user *buf,
task->signal->oom_score_adj = oom_adj;
trace_oom_score_adj_update(task);
-err_sighand:
- unlock_task_sighand(task, &flags);
-err_put_task:
+err_unlock:
+ mutex_unlock(&oom_adj_mutex);
put_task_struct(task);
out:
return err < 0 ? err : count;
@@ -1133,15 +1125,11 @@ static ssize_t oom_score_adj_read(struct file *file, char __user *buf,
struct task_struct *task = get_proc_task(file_inode(file));
char buffer[PROC_NUMBUF];
short oom_score_adj = OOM_SCORE_ADJ_MIN;
- unsigned long flags;
size_t len;
if (!task)
return -ESRCH;
- if (lock_task_sighand(task, &flags)) {
- oom_score_adj = task->signal->oom_score_adj;
- unlock_task_sighand(task, &flags);
- }
+ oom_score_adj = task->signal->oom_score_adj;
put_task_struct(task);
len = snprintf(buffer, sizeof(buffer), "%hd\n", oom_score_adj);
return simple_read_from_buffer(buf, count, ppos, buffer, len);
@@ -1152,7 +1140,6 @@ static ssize_t oom_score_adj_write(struct file *file, const char __user *buf,
{
struct task_struct *task;
char buffer[PROC_NUMBUF];
- unsigned long flags;
int oom_score_adj;
int err;
@@ -1179,25 +1166,21 @@ static ssize_t oom_score_adj_write(struct file *file, const char __user *buf,
goto out;
}
- if (!lock_task_sighand(task, &flags)) {
- err = -ESRCH;
- goto err_put_task;
- }
-
+ mutex_lock(&oom_adj_mutex);
if ((short)oom_score_adj < task->signal->oom_score_adj_min &&
!capable(CAP_SYS_RESOURCE)) {
err = -EACCES;
- goto err_sighand;
+ goto err_unlock;
}
task->signal->oom_score_adj = (short)oom_score_adj;
if (has_capability_noaudit(current, CAP_SYS_RESOURCE))
task->signal->oom_score_adj_min = (short)oom_score_adj;
+
trace_oom_score_adj_update(task);
-err_sighand:
- unlock_task_sighand(task, &flags);
-err_put_task:
+err_unlock:
+ mutex_unlock(&oom_adj_mutex);
put_task_struct(task);
out:
return err < 0 ? err : count;
--
2.8.1
next prev parent reply other threads:[~2016-06-20 12:44 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-06-20 12:43 [PATCH 0/10 -v5] Handle oom bypass more gracefully Michal Hocko
2016-06-20 12:43 ` [PATCH 01/10] proc, oom: drop bogus task_lock and mm check Michal Hocko
2016-06-20 12:43 ` Michal Hocko [this message]
2016-06-20 12:43 ` [PATCH 03/10] proc, oom_adj: extract oom_score_adj setting into a helper Michal Hocko
2016-06-20 12:43 ` [PATCH 04/10] mm, oom_adj: make sure processes sharing mm have same view of oom_score_adj Michal Hocko
2016-06-20 12:43 ` [PATCH 05/10] mm, oom: skip vforked tasks from being selected Michal Hocko
2016-06-20 12:43 ` [PATCH 06/10] mm, oom: kill all tasks sharing the mm Michal Hocko
2016-06-20 12:43 ` [PATCH 07/10] mm, oom: fortify task_will_free_mem Michal Hocko
2016-06-20 12:43 ` [PATCH 08/10] mm, oom: task_will_free_mem should skip oom_reaped tasks Michal Hocko
2016-06-20 12:43 ` [PATCH 09/10] mm, oom_reaper: do not attempt to reap a task more than twice Michal Hocko
2016-06-20 12:43 ` [PATCH 10/10] mm, oom: hide mm which is shared with kthread or global init Michal Hocko
2016-07-19 12:05 ` Michal Hocko
2016-07-19 23:27 ` Andrew Morton
2016-07-20 6:29 ` Michal Hocko
-- strict thread matches above, loose matches on Subject: below --
2016-06-09 11:52 [PATCH 0/10 -v4] Handle oom bypass more gracefully Michal Hocko
2016-06-09 11:52 ` [PATCH 02/10] proc, oom: drop bogus sighand lock Michal Hocko
2016-06-03 9:16 [PATCH 0/10 -v3] Handle oom bypass more gracefully Michal Hocko
2016-06-03 9:16 ` [PATCH 02/10] proc, oom: drop bogus sighand lock Michal Hocko
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