4.4-stable review patch. If anyone has any objections, please let me know.
------------------
From: Mateusz Guzik <mguzik@xxxxxxxxxx>
commit cd81a9170e69e018bbaba547c1fd85a585f5697a upstream.
For more convenient access if one has a pointer to the task.
As a minor nit take advantage of the fact that only task lock + rcu are
needed to safely grab ->exe_file. This saves mm refcount dance.
Use the helper in proc_exe_link.
Signed-off-by: Mateusz Guzik <mguzik@xxxxxxxxxx>
Acked-by: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx>
Acked-by: Richard Guy Briggs <rgb@xxxxxxxxxx>
Signed-off-by: Paul Moore <paul@xxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
fs/proc/base.c | 7 +------
include/linux/mm.h | 1 +
kernel/fork.c | 23 +++++++++++++++++++++++
3 files changed, 25 insertions(+), 6 deletions(-)
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -1545,18 +1545,13 @@ static const struct file_operations proc
static int proc_exe_link(struct dentry *dentry, struct path *exe_path)
{
struct task_struct *task;
- struct mm_struct *mm;
struct file *exe_file;
task = get_proc_task(d_inode(dentry));
if (!task)
return -ENOENT;
- mm = get_task_mm(task);
+ exe_file = get_task_exe_file(task);
put_task_struct(task);
- if (!mm)
- return -ENOENT;
- exe_file = get_mm_exe_file(mm);
- mmput(mm);
if (exe_file) {
*exe_path = exe_file->f_path;
path_get(&exe_file->f_path);
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1898,6 +1898,7 @@ extern void mm_drop_all_locks(struct mm_
extern void set_mm_exe_file(struct mm_struct *mm, struct file *new_exe_file);
extern struct file *get_mm_exe_file(struct mm_struct *mm);
+extern struct file *get_task_exe_file(struct task_struct *task);
extern int may_expand_vm(struct mm_struct *mm, unsigned long npages);
extern struct vm_area_struct *_install_special_mapping(struct mm_struct *mm,
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -764,6 +764,29 @@ struct file *get_mm_exe_file(struct mm_s
EXPORT_SYMBOL(get_mm_exe_file);
/**
+ * get_task_exe_file - acquire a reference to the task's executable file
+ *
+ * Returns %NULL if task's mm (if any) has no associated executable file or
+ * this is a kernel thread with borrowed mm (see the comment above get_task_mm).
+ * User must release file via fput().
+ */
+struct file *get_task_exe_file(struct task_struct *task)
+{
+ struct file *exe_file = NULL;
+ struct mm_struct *mm;
+
+ task_lock(task);
+ mm = task->mm;
+ if (mm) {
+ if (!(task->flags & PF_KTHREAD))
+ exe_file = get_mm_exe_file(mm);
+ }
+ task_unlock(task);
+ return exe_file;
+}
+EXPORT_SYMBOL(get_task_exe_file);
+
+/**
* get_task_mm - acquire a reference to the task's mm
*
* Returns %NULL if the task has no mm. Checks PF_KTHREAD (meaning
--
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