Commit 11163348 authored by Davidlohr Bueso's avatar Davidlohr Bueso Committed by Linus Torvalds

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: default avatarDavidlohr Bueso <dbueso@suse.de>
Cc: Robert Richter <rric@kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 15beb694
...@@ -21,6 +21,7 @@ ...@@ -21,6 +21,7 @@
* objects. * objects.
*/ */
#include <linux/file.h>
#include <linux/mm.h> #include <linux/mm.h>
#include <linux/workqueue.h> #include <linux/workqueue.h>
#include <linux/notifier.h> #include <linux/notifier.h>
...@@ -224,10 +225,18 @@ static inline unsigned long fast_get_dcookie(struct path *path) ...@@ -224,10 +225,18 @@ static inline unsigned long fast_get_dcookie(struct path *path)
static unsigned long get_exec_dcookie(struct mm_struct *mm) static unsigned long get_exec_dcookie(struct mm_struct *mm)
{ {
unsigned long cookie = NO_COOKIE; unsigned long cookie = NO_COOKIE;
struct file *exe_file;
if (mm && mm->exe_file) if (!mm)
cookie = fast_get_dcookie(&mm->exe_file->f_path); 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; return cookie;
} }
...@@ -236,6 +245,8 @@ static unsigned long get_exec_dcookie(struct mm_struct *mm) ...@@ -236,6 +245,8 @@ static unsigned long get_exec_dcookie(struct mm_struct *mm)
* pair that can then be added to the global event buffer. We make * 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 * sure to do this lookup before a mm->mmap modification happens so
* we don't lose track. * we don't lose track.
*
* The caller must ensure the mm is not nil (ie: not a kernel thread).
*/ */
static unsigned long static unsigned long
lookup_dcookie(struct mm_struct *mm, unsigned long addr, off_t *offset) lookup_dcookie(struct mm_struct *mm, unsigned long addr, off_t *offset)
...@@ -243,6 +254,7 @@ lookup_dcookie(struct mm_struct *mm, unsigned long addr, off_t *offset) ...@@ -243,6 +254,7 @@ lookup_dcookie(struct mm_struct *mm, unsigned long addr, off_t *offset)
unsigned long cookie = NO_COOKIE; unsigned long cookie = NO_COOKIE;
struct vm_area_struct *vma; struct vm_area_struct *vma;
down_read(&mm->mmap_sem);
for (vma = find_vma(mm, addr); vma; vma = vma->vm_next) { for (vma = find_vma(mm, addr); vma; vma = vma->vm_next) {
if (addr < vma->vm_start || addr >= vma->vm_end) if (addr < vma->vm_start || addr >= vma->vm_end)
...@@ -262,6 +274,7 @@ lookup_dcookie(struct mm_struct *mm, unsigned long addr, off_t *offset) ...@@ -262,6 +274,7 @@ lookup_dcookie(struct mm_struct *mm, unsigned long addr, off_t *offset)
if (!vma) if (!vma)
cookie = INVALID_COOKIE; cookie = INVALID_COOKIE;
up_read(&mm->mmap_sem);
return cookie; return cookie;
} }
...@@ -402,20 +415,9 @@ static void release_mm(struct mm_struct *mm) ...@@ -402,20 +415,9 @@ static void release_mm(struct mm_struct *mm)
{ {
if (!mm) if (!mm)
return; return;
up_read(&mm->mmap_sem);
mmput(mm); 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) static inline int is_code(unsigned long val)
{ {
return val == ESCAPE_CODE; return val == ESCAPE_CODE;
...@@ -532,7 +534,7 @@ void sync_buffer(int cpu) ...@@ -532,7 +534,7 @@ void sync_buffer(int cpu)
new = (struct task_struct *)val; new = (struct task_struct *)val;
oldmm = mm; oldmm = mm;
release_mm(oldmm); release_mm(oldmm);
mm = take_tasks_mm(new); mm = get_task_mm(new);
if (mm != oldmm) if (mm != oldmm)
cookie = get_exec_dcookie(mm); cookie = get_exec_dcookie(mm);
add_user_ctx_switch(new, cookie); add_user_ctx_switch(new, cookie);
......
...@@ -752,6 +752,7 @@ struct file *get_mm_exe_file(struct mm_struct *mm) ...@@ -752,6 +752,7 @@ struct file *get_mm_exe_file(struct mm_struct *mm)
rcu_read_unlock(); rcu_read_unlock();
return exe_file; return exe_file;
} }
EXPORT_SYMBOL(get_mm_exe_file);
/** /**
* get_task_mm - acquire a reference to the task's mm * get_task_mm - acquire a reference to the task's mm
......
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