[PATCH 2/6] proc, oom_adj: extract oom_score_adj setting into a helper

[Michal Hocko <mhocko@kernel.org>]

From: Michal Hocko <mhocko@suse.com>

Currently we have two proc interfaces to set oom_score_adj. The legacy
/proc/<pid>/oom_adj and /proc/<pid>/oom_score_adj which both have their
specific handlers. Big part of the logic is duplicated so extract the
common code into __set_oom_adj helper. Legacy knob still expects some
details slightly different so make sure those are handled same way - e.g.
the legacy mode ignores oom_score_adj_min and it warns about the usage.

This patch shouldn't introduce any functional changes.

Signed-off-by: Michal Hocko <mhocko@suse.com>
---
 fs/proc/base.c | 133 +++++++++++++++++++++++++--------------------------------
 1 file changed, 59 insertions(+), 74 deletions(-)

diff --git a/fs/proc/base.c b/fs/proc/base.c
index be73f4d0cb01..23679673bf5a 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -1041,6 +1041,63 @@ static ssize_t oom_adj_read(struct file *file, char __user *buf, size_t count,
 	return simple_read_from_buffer(buf, count, ppos, buffer, len);
 }
 
+static int __set_oom_adj(struct file *file, int oom_adj, bool legacy)
+{
+	struct task_struct *task;
+	unsigned long flags;
+	int err = 0;
+
+	task = get_proc_task(file_inode(file));
+	if (!task) {
+		err = -ESRCH;
+		goto out;
+	}
+
+	task_lock(task);
+	if (!task->mm) {
+		err = -EINVAL;
+		goto err_task_lock;
+	}
+
+	if (!lock_task_sighand(task, &flags)) {
+		err = -ESRCH;
+		goto err_task_lock;
+	}
+
+	if (legacy) {
+		if (oom_adj < task->signal->oom_score_adj &&
+				!capable(CAP_SYS_RESOURCE)) {
+			err = -EACCES;
+			goto err_sighand;
+		}
+		/*
+		 * /proc/pid/oom_adj is provided for legacy purposes, ask users to use
+		 * /proc/pid/oom_score_adj instead.
+		 */
+		pr_warn_once("%s (%d): /proc/%d/oom_adj is deprecated, please use /proc/%d/oom_score_adj instead.\n",
+			  current->comm, task_pid_nr(current), task_pid_nr(task),
+			  task_pid_nr(task));
+	} else {
+		if ((short)oom_adj < task->signal->oom_score_adj_min &&
+				!capable(CAP_SYS_RESOURCE)) {
+			err = -EACCES;
+			goto err_sighand;
+		}
+	}
+
+	task->signal->oom_score_adj = oom_adj;
+	if (!legacy && has_capability_noaudit(current, CAP_SYS_RESOURCE))
+		task->signal->oom_score_adj_min = (short)oom_adj;
+	trace_oom_score_adj_update(task);
+err_sighand:
+	unlock_task_sighand(task, &flags);
+err_task_lock:
+	task_unlock(task);
+	put_task_struct(task);
+out:
+	return err;
+}
+
 /*
  * /proc/pid/oom_adj exists solely for backwards compatibility with previous
  * kernels.  The effective policy is defined by oom_score_adj, which has a
@@ -1054,10 +1111,8 @@ static ssize_t oom_adj_read(struct file *file, char __user *buf, size_t count,
 static ssize_t oom_adj_write(struct file *file, const char __user *buf,
 			     size_t count, loff_t *ppos)
 {
-	struct task_struct *task;
 	char buffer[PROC_NUMBUF];
 	int oom_adj;
-	unsigned long flags;
 	int err;
 
 	memset(buffer, 0, sizeof(buffer));
@@ -1077,23 +1132,6 @@ static ssize_t oom_adj_write(struct file *file, const char __user *buf,
 		goto out;
 	}
 
-	task = get_proc_task(file_inode(file));
-	if (!task) {
-		err = -ESRCH;
-		goto out;
-	}
-
-	task_lock(task);
-	if (!task->mm) {
-		err = -EINVAL;
-		goto err_task_lock;
-	}
-
-	if (!lock_task_sighand(task, &flags)) {
-		err = -ESRCH;
-		goto err_task_lock;
-	}
-
 	/*
 	 * Scale /proc/pid/oom_score_adj appropriately ensuring that a maximum
 	 * value is always attainable.
@@ -1103,27 +1141,8 @@ static ssize_t oom_adj_write(struct file *file, const char __user *buf,
 	else
 		oom_adj = (oom_adj * OOM_SCORE_ADJ_MAX) / -OOM_DISABLE;
 
-	if (oom_adj < task->signal->oom_score_adj &&
-	    !capable(CAP_SYS_RESOURCE)) {
-		err = -EACCES;
-		goto err_sighand;
-	}
-
-	/*
-	 * /proc/pid/oom_adj is provided for legacy purposes, ask users to use
-	 * /proc/pid/oom_score_adj instead.
-	 */
-	pr_warn_once("%s (%d): /proc/%d/oom_adj is deprecated, please use /proc/%d/oom_score_adj instead.\n",
-		  current->comm, task_pid_nr(current), task_pid_nr(task),
-		  task_pid_nr(task));
+	err = __set_oom_adj(file, oom_adj, true);
 
-	task->signal->oom_score_adj = oom_adj;
-	trace_oom_score_adj_update(task);
-err_sighand:
-	unlock_task_sighand(task, &flags);
-err_task_lock:
-	task_unlock(task);
-	put_task_struct(task);
 out:
 	return err < 0 ? err : count;
 }
@@ -1157,9 +1176,7 @@ static ssize_t oom_score_adj_read(struct file *file, char __user *buf,
 static ssize_t oom_score_adj_write(struct file *file, const char __user *buf,
 					size_t count, loff_t *ppos)
 {
-	struct task_struct *task;
 	char buffer[PROC_NUMBUF];
-	unsigned long flags;
 	int oom_score_adj;
 	int err;
 
@@ -1180,39 +1197,7 @@ static ssize_t oom_score_adj_write(struct file *file, const char __user *buf,
 		goto out;
 	}
 
-	task = get_proc_task(file_inode(file));
-	if (!task) {
-		err = -ESRCH;
-		goto out;
-	}
-
-	task_lock(task);
-	if (!task->mm) {
-		err = -EINVAL;
-		goto err_task_lock;
-	}
-
-	if (!lock_task_sighand(task, &flags)) {
-		err = -ESRCH;
-		goto err_task_lock;
-	}
-
-	if ((short)oom_score_adj < task->signal->oom_score_adj_min &&
-			!capable(CAP_SYS_RESOURCE)) {
-		err = -EACCES;
-		goto err_sighand;
-	}
-
-	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_task_lock:
-	task_unlock(task);
-	put_task_struct(task);
+	err = __set_oom_adj(file, oom_score_adj, false);
 out:
 	return err < 0 ? err : count;
 }
-- 
2.8.1