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

drivers/oprofile/buffer_sync.c

+16 −14
Original line number Diff line number Diff line
@@ -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 inline unsigned long fast_get_dcookie(struct path *path) 
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 @@ static unsigned long get_exec_dcookie(struct mm_struct *mm) 
 * 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 @@ lookup_dcookie(struct mm_struct *mm, unsigned long addr, off_t *offset) 
	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 @@ lookup_dcookie(struct mm_struct *mm, unsigned long addr, off_t *offset) 


	if (!vma)

		cookie = INVALID_COOKIE;

	up_read(&mm->mmap_sem);



	return cookie;

}
@@ -402,20 +415,9 @@ static void release_mm(struct mm_struct *mm) 
{

	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 @@ void sync_buffer(int cpu) 
				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);

kernel/fork.c

+1 −0
Original line number Diff line number Diff line
@@ -752,6 +752,7 @@ struct file *get_mm_exe_file(struct mm_struct *mm) 
	rcu_read_unlock();

	return exe_file;

}

EXPORT_SYMBOL(get_mm_exe_file);



/**

 * get_task_mm - acquire a reference to the task's mm