From: Hugh Dickins <hugh@veritas.com>
Clarify mmgrab by collapsing it into get_task_mm (in fork.c not inline),
and commenting on the special case it is guarding against: when use_mm in
an AIO daemon temporarily adopts the mm while it's on its way out.
Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
---
25-akpm/fs/proc/array.c | 6 +-----
25-akpm/include/linux/sched.h | 24 ++----------------------
25-akpm/kernel/fork.c | 38 ++++++++++++++++++++++++++------------
3 files changed, 29 insertions(+), 39 deletions(-)
diff -puN fs/proc/array.c~clarify-get_task_mm-mmgrab fs/proc/array.c
--- 25/fs/proc/array.c~clarify-get_task_mm-mmgrab Fri Aug 6 15:20:09 2004
+++ 25-akpm/fs/proc/array.c Fri Aug 6 15:20:09 2004
@@ -312,11 +312,7 @@ int proc_pid_stat(struct task_struct *ta
state = *get_task_state(task);
vsize = eip = esp = 0;
- task_lock(task);
- mm = task->mm;
- if(mm)
- mm = mmgrab(mm);
- task_unlock(task);
+ mm = get_task_mm(task);
if (mm) {
down_read(&mm->mmap_sem);
vsize = task_vsize(mm);
diff -puN include/linux/sched.h~clarify-get_task_mm-mmgrab include/linux/sched.h
--- 25/include/linux/sched.h~clarify-get_task_mm-mmgrab Fri Aug 6 15:20:09 2004
+++ 25-akpm/include/linux/sched.h Fri Aug 6 15:20:09 2004
@@ -795,8 +795,8 @@ static inline void mmdrop(struct mm_stru
/* mmput gets rid of the mappings and all user-space */
extern void mmput(struct mm_struct *);
-/* Grab a reference to the mm if its not already going away */
-extern struct mm_struct *mmgrab(struct mm_struct *);
+/* Grab a reference to a task's mm, if it is not already going away */
+extern struct mm_struct *get_task_mm(struct task_struct *task);
/* Remove the current tasks stale references to the old mm_struct */
extern void mm_release(struct task_struct *, struct mm_struct *);
@@ -897,27 +897,7 @@ static inline void task_unlock(struct ta
{
spin_unlock(&p->alloc_lock);
}
-
-/**
- * get_task_mm - acquire a reference to the task's mm
- *
- * Returns %NULL if the task has no mm. User must release
- * the mm via mmput() after use.
- */
-static inline struct mm_struct * get_task_mm(struct task_struct * task)
-{
- struct mm_struct * mm;
-
- task_lock(task);
- mm = task->mm;
- if (mm)
- mm = mmgrab(mm);
- task_unlock(task);
- return mm;
-}
-
-
/* set thread flags in other task's structures
* - see asm/thread_info.h for TIF_xxxx flags available
*/
diff -puN kernel/fork.c~clarify-get_task_mm-mmgrab kernel/fork.c
--- 25/kernel/fork.c~clarify-get_task_mm-mmgrab Fri Aug 6 15:20:09 2004
+++ 25-akpm/kernel/fork.c Fri Aug 6 15:20:09 2004
@@ -483,20 +483,34 @@ void mmput(struct mm_struct *mm)
}
}
-/*
- * Checks if the use count of an mm is non-zero and if so
- * returns a reference to it after bumping up the use count.
- * If the use count is zero, it means this mm is going away,
- * so return NULL.
+/**
+ * get_task_mm - acquire a reference to the task's mm
+ *
+ * Returns %NULL if the task has no mm. Checks if the use count
+ * of the mm is non-zero and if so returns a reference to it, after
+ * bumping up the use count. User must release the mm via mmput()
+ * after use. Typically used by /proc and ptrace.
+ *
+ * If the use count is zero, it means that this mm is going away,
+ * so return %NULL. This only happens in the case of an AIO daemon
+ * which has temporarily adopted an mm (see use_mm), in the course
+ * of its final mmput, before exit_aio has completed.
*/
-struct mm_struct *mmgrab(struct mm_struct *mm)
+struct mm_struct *get_task_mm(struct task_struct *task)
{
- spin_lock(&mmlist_lock);
- if (!atomic_read(&mm->mm_users))
- mm = NULL;
- else
- atomic_inc(&mm->mm_users);
- spin_unlock(&mmlist_lock);
+ struct mm_struct *mm;
+
+ task_lock(task);
+ mm = task->mm;
+ if (mm) {
+ spin_lock(&mmlist_lock);
+ if (!atomic_read(&mm->mm_users))
+ mm = NULL;
+ else
+ atomic_inc(&mm->mm_users);
+ spin_unlock(&mmlist_lock);
+ }
+ task_unlock(task);
return mm;
}
_