linux-kernel - Re: [PATCH] After swapout/swapin private dirty mappings become clean

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20100915092239.C9D9.A69D9226@jp.fujitsu.com>
Date:	Wed, 15 Sep 2010 09:24:31 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Nikanth Karthikesan <knikanth@...e.de>
Cc:	kosaki.motohiro@...fujitsu.com, linux-mm@...ck.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Matt Mackall <mpm@...enic.com>,
	balbir@...ux.vnet.ibm.com, rguenther@...ell.com, matz@...ell.com
Subject: Re: [PATCH] After swapout/swapin private dirty mappings become clean

> /proc/$pid/smaps broken: After swapout/swapin private dirty mappings become
> clean.
> 
> When a page with private file mapping becomes dirty, the vma will be in both
> i_mmap tree and anon_vma list. The /proc/$pid/smaps will account these pages
> as dirty and backed by the file.
> 
> But when those dirty pages gets swapped out, and when they are read back from
> swap, they would be marked as clean, as it should be, as they are part of swap
> cache now.
> 
> But the /proc/$pid/smaps would report the vma as a mapping of a file and it is
> clean. The pages are actually in same state i.e., dirty with respect to file
> still, but which was once reported as dirty is now being reported as clean to
> user-space.
> 
> This confuses tools like gdb which uses this information. Those tools think
> that those pages were never modified and it creates problem when they create
> dumps.
> 
> The file mapping of the vma also cannot be broken as pages never read earlier,
> will still have to come from the file. Just that those dirty pages have become
> clean anonymous pages.
> 
> During swaping in, restoring the exact state as dirty file-backed pages before
> swapout would be useless, as there in no real bug. Breaking the vma with only
> anonymous pages as seperate vmas unnecessary may not be a good thing as well.
> So let us just export the information that a file-backed vma has anonymous
> dirty pages.

Why can't gdb check Swap: field in smaps? I think Swap!=0 mean we need dump out.

Am I missing anything?

 - kosaki

> 
> Export this information in smaps by prepending file-names with "[anon]+", when
> some of the pages in a file backed vma become anonymous.
> 
> Signed-off-by: Nikanth Karthikesan <knikanth@...e.de>
> 
> ---
> 
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index 439fc1f..68f9806 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -242,6 +242,8 @@ static void show_map_vma(struct seq_file *m, struct vm_area_struct *vma)
>  	 */
>  	if (file) {
>  		pad_len_spaces(m, len);
> +		if (vma->anon_vma)
> +			seq_puts(m, "[anon]+");
>  		seq_path(m, &file->f_path, "\n");
>  	} else {
>  		const char *name = arch_vma_name(vma);
> 
> 
> --
> To unsubscribe, send a message with 'unsubscribe linux-mm' in
> the body to majordomo@...ck.org.  For more info on Linux MM,
> see: http://www.linux-mm.org/ .
> Don't email: <a href=mailto:"dont@...ck.org"> email@...ck.org </a>
> 



--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/