Commit f913da59 authored by Michal Hocko's avatar Michal Hocko Committed by Linus Torvalds
Browse files

proc, oom: drop bogus sighand lock 



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 ea6d290c ("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: default avatarOleg Nesterov <oleg@redhat.com>
Link: http://lkml.kernel.org/r/1466426628-15074-3-git-send-email-mhocko@kernel.org


Signed-off-by: default avatarMichal Hocko <mhocko@suse.com>
Acked-by: default avatarOleg Nesterov <oleg@redhat.com>
Cc: Vladimir Davydov <vdavydov@virtuozzo.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent d49fbf76

fs/proc/base.c

+17 −34
Original line number Diff line number Diff line
@@ -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);

	}

	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);

	}

	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;

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