linux-kernel - Re: why does index in truncate_inode_pages

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Date:	Tue, 3 Dec 2013 15:02:14 +0100
From:	Jan Kara <jack@...e.cz>
To:	Toralf Förster <toralf.foerster@....de>
Cc:	UML devel <user-mode-linux-devel@...ts.sourceforge.net>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: why does index in truncate_inode_pages_range() grows so much ?

On Sun 24-11-13 16:14:21, Toralf Förster wrote:
> At a 32 bit guest UML with current kernel git tree I putted a printk
> into that function :
> 
> void truncate_inode_pages_range(struct address_space *mapping,
>                                 loff_t lstart, loff_t lend)
> {
> ...
> 
> 
>                 cond_resched();
>                 index++;
> 		printk ("            <------------
> 
> 
> 
> 
> and got (while fuzzying the UML guest with trinity) this output in the
> UML guest:
> 
> 
> Nov 24 12:06:53 trinity kernel: index:42 end:4294967295
> Nov 24 12:06:53 trinity kernel: index:43 end:4294967295
> Nov 24 12:06:53 trinity kernel: index:5 end:4294967295
> Nov 24 12:06:53 trinity kernel: index:1 end:4294967295
> Nov 24 12:06:53 trinity kernel: index:1 end:4294967295
> Nov 24 12:06:53 trinity kernel: index:1035468800 end:4294967295
> Nov 24 12:06:53 trinity kernel: index:1 end:4294967295
> Nov 24 12:06:53 trinity kernel: index:1 end:4294967295
> Nov 24 12:06:53 trinity kernel: index:1 end:4294967295
> Nov 24 12:06:53 trinity kernel: index:16 end:4294967295
> Nov 24 12:06:53 trinity kernel: index:1 end:4294967295
> Nov 24 12:06:53 trinity kernel: index:4 end:4294967295
> Nov 24 12:06:53 trinity kernel: index:2 end:4294967295
> Nov 24 12:06:53 trinity kernel: index:1 end:4294967295
> Nov 24 12:06:53 trinity kernel: index:4184867847 end:4294967295
> Nov 24 12:06:53 trinity kernel: index:1 end:4294967295
> Nov 24 12:06:53 trinity kernel: index:3 end:4294967295
> Nov 24 12:06:53 trinity kernel: index:1727 end:4294967295
> Nov 24 12:06:53 trinity kernel: index:1 end:4294967295
> 
> 
> I'm wondering if index is expected to become sometimes so big.
  No, I wouldn't expect such huge indices. OTOH with fuzzing there could be
some valid explanations. Could you move the printk before
pagevec_release(), print also 'start' variable and in case 'index' is
suspiciously large, print also 'i' and some info about the page pvec[i]
page (page->index, page->flags, page->mapping->host->i_sb->s_id,
page->mapping->host->i_ino)?

								Honza
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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