[PATCH 4/5] fs/proc/task_mmu.c: introduce the "stable" proc_maps_private->mm

[Oleg Nesterov <oleg@redhat.com>]

A separate change to simplify the review of the next one.

Add the new "mm_struct *mm" member into struct proc_maps_private, it is
initialized by proc_maps_open() at "open" time.

This obviously means that proc_maps_open() users should additionally do
mmdrop() in fop->release(), add the new helper, proc_map_release().

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
 fs/proc/internal.h |    1 +
 fs/proc/task_mmu.c |   31 +++++++++++++++++++++++++------
 2 files changed, 26 insertions(+), 6 deletions(-)

diff --git a/fs/proc/internal.h b/fs/proc/internal.h
index ba0c1c1..78784cd 100644
--- a/fs/proc/internal.h
+++ b/fs/proc/internal.h
@@ -267,6 +267,7 @@ extern int proc_remount(struct super_block *, int *, char *);
 struct proc_maps_private {
 	struct pid *pid;
 	struct task_struct *task;
+	struct mm_struct *mm;
 #ifdef CONFIG_MMU
 	struct vm_area_struct *tail_vma;
 #endif
diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 794aeb6..1cc623d 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -240,9 +240,28 @@ static int proc_maps_open(struct inode *inode, struct file *file,
 		return -ENOMEM;
 
 	priv->pid = proc_pid(inode);
+	priv->mm = proc_mem_open(inode, PTRACE_MODE_READ);
+	if (IS_ERR(priv->mm)) {
+		int err = PTR_ERR(priv->mm);
+		seq_release_private(inode, file);
+		return err;
+	}
+
 	return 0;
 }
 
+static int proc_map_release(struct inode *inode, struct file *file)
+{
+	struct seq_file *seq = file->private_data;
+	struct proc_maps_private *priv = seq->private;
+
+	if (priv->mm)
+		mmdrop(priv->mm);
+
+	return seq_release_private(inode, file);
+}
+
+
 static int do_maps_open(struct inode *inode, struct file *file,
 			const struct seq_operations *ops)
 {
@@ -398,14 +417,14 @@ const struct file_operations proc_pid_maps_operations = {
 	.open		= pid_maps_open,
 	.read		= seq_read,
 	.llseek		= seq_lseek,
-	.release	= seq_release_private,
+	.release	= proc_map_release,
 };
 
 const struct file_operations proc_tid_maps_operations = {
 	.open		= tid_maps_open,
 	.read		= seq_read,
 	.llseek		= seq_lseek,
-	.release	= seq_release_private,
+	.release	= proc_map_release,
 };
 
 /*
@@ -680,14 +699,14 @@ const struct file_operations proc_pid_smaps_operations = {
 	.open		= pid_smaps_open,
 	.read		= seq_read,
 	.llseek		= seq_lseek,
-	.release	= seq_release_private,
+	.release	= proc_map_release,
 };
 
 const struct file_operations proc_tid_smaps_operations = {
 	.open		= tid_smaps_open,
 	.read		= seq_read,
 	.llseek		= seq_lseek,
-	.release	= seq_release_private,
+	.release	= proc_map_release,
 };
 
 /*
@@ -1520,13 +1539,13 @@ const struct file_operations proc_pid_numa_maps_operations = {
 	.open		= pid_numa_maps_open,
 	.read		= seq_read,
 	.llseek		= seq_lseek,
-	.release	= seq_release_private,
+	.release	= proc_map_release,
 };
 
 const struct file_operations proc_tid_numa_maps_operations = {
 	.open		= tid_numa_maps_open,
 	.read		= seq_read,
 	.llseek		= seq_lseek,
-	.release	= seq_release_private,
+	.release	= proc_map_release,
 };
 #endif /* CONFIG_NUMA */
-- 
1.5.5.1