oprofile: reduce mmap_sem hold for mm->exe_file
sync_buffer() needs the mmap_sem for two distinct operations, both only
occurring upon user context switch handling:
1) Dealing with the exe_file.
2) Adding the dcookie data as we need to lookup the vma that
backs it. This is done via add_sample() and add_data().
This patch isolates 1), for it will no longer need the mmap_sem for
serialization. However, for now, make of the more standard
get_mm_exe_file(), requiring only holding the mmap_sem to read the value,
and relying on reference counting to make sure that the exe file won't
dissappear underneath us while doing the get dcookie.
As a consequence, for 2) we move the mmap_sem locking into where we really
need it, in lookup_dcookie(). The benefits are twofold: reduce mmap_sem
hold times, and cleaner code.
[akpm@linux-foundation.org: export get_mm_exe_file for arch/x86/oprofile/oprofile.ko]
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Cc: Robert Richter <rric@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/drivers/oprofile/buffer_sync.c b/drivers/oprofile/buffer_sync.c
index d93b2b6..82f7000 100644
--- a/drivers/oprofile/buffer_sync.c
+++ b/drivers/oprofile/buffer_sync.c
@@ -21,6 +21,7 @@
* objects.
*/
+#include <linux/file.h>
#include <linux/mm.h>
#include <linux/workqueue.h>
#include <linux/notifier.h>
@@ -224,10 +225,18 @@
static unsigned long get_exec_dcookie(struct mm_struct *mm)
{
unsigned long cookie = NO_COOKIE;
+ struct file *exe_file;
- if (mm && mm->exe_file)
- cookie = fast_get_dcookie(&mm->exe_file->f_path);
+ if (!mm)
+ goto done;
+ exe_file = get_mm_exe_file(mm);
+ if (!exe_file)
+ goto done;
+
+ cookie = fast_get_dcookie(&exe_file->f_path);
+ fput(exe_file);
+done:
return cookie;
}
@@ -236,6 +245,8 @@
* pair that can then be added to the global event buffer. We make
* sure to do this lookup before a mm->mmap modification happens so
* we don't lose track.
+ *
+ * The caller must ensure the mm is not nil (ie: not a kernel thread).
*/
static unsigned long
lookup_dcookie(struct mm_struct *mm, unsigned long addr, off_t *offset)
@@ -243,6 +254,7 @@
unsigned long cookie = NO_COOKIE;
struct vm_area_struct *vma;
+ down_read(&mm->mmap_sem);
for (vma = find_vma(mm, addr); vma; vma = vma->vm_next) {
if (addr < vma->vm_start || addr >= vma->vm_end)
@@ -262,6 +274,7 @@
if (!vma)
cookie = INVALID_COOKIE;
+ up_read(&mm->mmap_sem);
return cookie;
}
@@ -402,20 +415,9 @@
{
if (!mm)
return;
- up_read(&mm->mmap_sem);
mmput(mm);
}
-
-static struct mm_struct *take_tasks_mm(struct task_struct *task)
-{
- struct mm_struct *mm = get_task_mm(task);
- if (mm)
- down_read(&mm->mmap_sem);
- return mm;
-}
-
-
static inline int is_code(unsigned long val)
{
return val == ESCAPE_CODE;
@@ -532,7 +534,7 @@
new = (struct task_struct *)val;
oldmm = mm;
release_mm(oldmm);
- mm = take_tasks_mm(new);
+ mm = get_task_mm(new);
if (mm != oldmm)
cookie = get_exec_dcookie(mm);
add_user_ctx_switch(new, cookie);
diff --git a/kernel/fork.c b/kernel/fork.c
index 0d23e76..03c1eaa 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -752,6 +752,7 @@
rcu_read_unlock();
return exe_file;
}
+EXPORT_SYMBOL(get_mm_exe_file);
/**
* get_task_mm - acquire a reference to the task's mm