Commit 48d212a2 authored by Linus Torvalds's avatar Linus Torvalds
Browse files

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



This reverts commit 40af1bbd.

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: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 46edaeda

fs/exec.c

+1 −0
Original line number Diff line number Diff line
@@ -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) {

kernel/exit.c

+5 −8
Original line number Diff line number Diff line
@@ -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);

kernel/fork.c

+0 −8
Original line number Diff line number Diff line
@@ -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);

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