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

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Date:	Fri, 08 Jun 2012 17:29:04 +0400
From:	Konstantin Khlebnikov <khlebnikov@...nvz.org>
To:	Oleg Nesterov <oleg@...hat.com>
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

Oleg Nesterov wrote:
> 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.

Patch below broken: it removes one hunk from kernel/exit.c twice.
And it does not add anything into mm_release().

>
> 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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