mm, oom: reintroduce /proc/pid/oom_adj

This is mostly a revert of 01dc52ebdf47 ("oom: remove deprecated oom_adj")
from Davidlohr Bueso.

It reintroduces /proc/pid/oom_adj for backwards compatibility with earlier
kernels.  It simply scales the value linearly when /proc/pid/oom_score_adj
is written.

The major difference is that its scheduled removal is no longer included
in Documentation/feature-removal-schedule.txt.  We do warn users with a
single printk, though, to suggest the more powerful and supported
/proc/pid/oom_score_adj interface.

Reported-by: Artem S. Tashkinov <t.artem@lycos.com>
Signed-off-by: David Rientjes <rientjes@google.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 109 insertions, 0 deletions

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 144a96732dd7..3c231adf8450 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -873,6 +873,113 @@ static const struct file_operations proc_environ_operations = {
         .release        = mem_release,
 };
 
+static ssize_t oom_adj_read(struct file *file, char __user *buf, size_t count,
+                            loff_t *ppos)
+{
+        struct task_struct *task = get_proc_task(file->f_path.dentry->d_inode);
+        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 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));
+        if (count > sizeof(buffer) - 1)
+                count = sizeof(buffer) - 1;
+        if (copy_from_user(buffer, buf, count)) {
+                err = -EFAULT;
+                goto out;
+        }
+
+        err = kstrtoint(strstrip(buffer), 0, &oom_adj);
+        if (err)
+                goto out;
+        if ((oom_adj < OOM_ADJUST_MIN || oom_adj > OOM_ADJUST_MAX) &&
+             oom_adj != OOM_DISABLE) {
+                err = -EINVAL;
+                goto out;
+        }
+
+        task = get_proc_task(file->f_path.dentry->d_inode);
+        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.
+         */
+        if (oom_adj == OOM_ADJUST_MAX)
+                oom_adj = OOM_SCORE_ADJ_MAX;
+        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.
+         */
+        printk_once(KERN_WARNING "%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));
+
+        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;
+}
+
+static const struct file_operations proc_oom_adj_operations = {
+        .read           = oom_adj_read,
+        .write          = oom_adj_write,
+        .llseek         = generic_file_llseek,
+};
+
 static ssize_t oom_score_adj_read(struct file *file, char __user *buf,
                                         size_t count, loff_t *ppos)
 {
@@ -2598,6 +2705,7 @@ static const struct pid_entry tgid_base_stuff[] = {
         REG("cgroup",  S_IRUGO, proc_cgroup_operations),
 #endif
         INF("oom_score",  S_IRUGO, proc_oom_score),
+        REG("oom_adj",    S_IRUGO|S_IWUSR, proc_oom_adj_operations),
         REG("oom_score_adj", S_IRUGO|S_IWUSR, proc_oom_score_adj_operations),
 #ifdef CONFIG_AUDITSYSCALL
         REG("loginuid",   S_IWUSR|S_IRUGO, proc_loginuid_operations),
@@ -2964,6 +3072,7 @@ static const struct pid_entry tid_base_stuff[] = {
         REG("cgroup",  S_IRUGO, proc_cgroup_operations),
 #endif
         INF("oom_score", S_IRUGO, proc_oom_score),
+        REG("oom_adj",   S_IRUGO|S_IWUSR, proc_oom_adj_operations),
         REG("oom_score_adj", S_IRUGO|S_IWUSR, proc_oom_score_adj_operations),
 #ifdef CONFIG_AUDITSYSCALL
         REG("loginuid",  S_IWUSR|S_IRUGO, proc_loginuid_operations),