linux-kernel - Re: [patch 12/12] mm: correctly synchronize rss-counters at exit/exec

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Date:	Fri, 8 Jun 2012 14:24:59 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Konstantin Khlebnikov <khlebnikov@...nvz.org>
Cc:	Hugh Dickins <hughd@...gle.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>,
	"kamezawa.hiroyu@...fujitsu.com" <kamezawa.hiroyu@...fujitsu.com>,
	"markus@...ppelsdorf.de" <markus@...ppelsdorf.de>,
	"stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: [patch 12/12] mm: correctly synchronize rss-counters at
	exit/exec

On 06/08, Konstantin Khlebnikov wrote:
>
> As result you can see "BUG: Bad rss-counter state mm:ffff88040783a680 idx:1 val:-1" in dmesg
>
> There left only one problem: nobody calls sync_mm_rss() after put_user() in mm_release().

Both callers call sync_mm_rss() to make check_mm() happy. But please
see the changelog, I think we should move it into mm_release(). See
the patch below (on top of v2 I sent). I need to recheck.

As for xacct_add_tsk(), yes it can "miss" that put_user(). But this
is what we have now, I think we do not care.

Oleg.

--- x/fs/exec.c
+++ x/fs/exec.c
@@ -822,7 +822,6 @@ static int exec_mmap(struct mm_struct *m
 	mm_release(tsk, old_mm);
 
 	if (old_mm) {
-		sync_mm_rss(old_mm);
 		/*
 		 * Make sure that if there is a core dump in progress
 		 * for the old mm, we get out and die instead of going
--- x/kernel/exit.c
+++ x/kernel/exit.c
@@ -656,7 +656,6 @@ static void exit_mm(struct task_struct *
 	if (!mm)
 		return;
 
-	sync_mm_rss(mm);
 	/*
 	 * Serialize with any possible pending coredump.
 	 * We must hold mmap_sem around checking core_state
--- x/kernel/taskstats.c
+++ x/kernel/taskstats.c
@@ -630,8 +630,7 @@ void taskstats_exit(struct task_struct *
 	if (!stats)
 		goto err;
 
-	if (tsk->mm)
-		sync_mm_rss(tsk->mm);
+	sync_mm_rss(tsk->mm);
 	fill_stats(tsk, stats);
 
 	/*
--- x/kernel/exit.c
+++ x/kernel/exit.c
@@ -656,7 +656,6 @@ static void exit_mm(struct task_struct *
 	if (!mm)
 		return;
 
-	sync_mm_rss(mm);
 	/*
 	 * Serialize with any possible pending coredump.
 	 * We must hold mmap_sem around checking core_state

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