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Revert "mm: correctly synchronize rss-counters at exit/exec"

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This reverts commit 40af1bbdca.

It's horribly and utterly broken for at least the following reasons:

 - calling sync_mm_rss() from mmput() is fundamentally wrong, because
   there's absolutely no reason to believe that the task that does the
   mmput() always does it on its own VM.  Example: fork, ptrace, /proc -
   you name it.

 - calling it *after* having done mmdrop() on it is doubly insane, since
   the mm struct may well be gone now.

 - testing mm against NULL before you call it is insane too, since a
NULL mm there would have caused oopses long before.

.. and those are just the three bugs I found before I decided to give up
looking for me and revert it asap.  I should have caught it before I
even took it, but I trusted Andrew too much.

Cc: Konstantin Khlebnikov <khlebnikov@openvz.org>
Cc: Markus Trippelsdorf <markus@trippelsdorf.de>
Cc: Hugh Dickins <hughd@google.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Linus Torvalds 2012-06-07 17:54:07 -07:00
parent 46edaedaf3
commit 48d212a2ee
3 changed files with 6 additions and 16 deletions
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1
fs/exec.c
View file

@ -819,6 +819,7 @@ static int exec_mmap(struct mm_struct *mm)
/* Notify parent that we're no longer interested in the old VM */
tsk = current;
old_mm = current->mm;
sync_mm_rss(old_mm);
mm_release(tsk, old_mm);
if (old_mm) {

13
kernel/exit.c
View file

@ -423,7 +423,6 @@ void daemonize(const char *name, ...)
* user space pages. We don't need them, and if we didn't close them
* they would be locked into memory.
*/
mm_release(current, current->mm);
exit_mm(current);
/*
* We don't want to get frozen, in case system-wide hibernation
@ -641,6 +640,7 @@ static void exit_mm(struct task_struct * tsk)
struct mm_struct *mm = tsk->mm;
struct core_state *core_state;
mm_release(tsk, mm);
if (!mm)
return;
/*
@ -960,13 +960,9 @@ void do_exit(long code)
preempt_count());
acct_update_integrals(tsk);
/* Set exit_code before complete_vfork_done() in mm_release() */
tsk->exit_code = code;
/* Release mm and sync mm's RSS info before statistics gathering */
mm_release(tsk, tsk->mm);
/* sync mm's RSS info before statistics gathering */
if (tsk->mm)
sync_mm_rss(tsk->mm);
group_dead = atomic_dec_and_test(&tsk->signal->live);
if (group_dead) {
hrtimer_cancel(&tsk->signal->real_timer);
@ -979,6 +975,7 @@ void do_exit(long code)
tty_audit_exit();
audit_free(tsk);
tsk->exit_code = code;
taskstats_exit(tsk, group_dead);
exit_mm(tsk);

8
kernel/fork.c
View file

@ -619,14 +619,6 @@ void mmput(struct mm_struct *mm)
module_put(mm->binfmt->module);
mmdrop(mm);
}
/*
* Final rss-counter synchronization. After this point there must be
* no pagefaults into this mm from the current context. Otherwise
* mm->rss_stat will be inconsistent.
*/
if (mm)
sync_mm_rss(mm);
}
EXPORT_SYMBOL_GPL(mmput);