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oprofile: reduce mmap_sem hold for mm->exe_file

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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>
This commit is contained in:
Davidlohr Bueso 2015-04-16 12:49:12 -07:00 committed by Linus Torvalds
parent 15beb694c6
commit 11163348a2
2 changed files with 17 additions and 14 deletions
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30
drivers/oprofile/buffer_sync.c
View File

@ -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);

1
kernel/fork.c
View File

@ -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