linux-ext4 - Re: [PATCH] ext3_getblk should handle HOLE correctly

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Date:	Thu, 07 Sep 2006 12:22:27 -0700
From:	Badari Pulavarty <pbadari@...ibm.com>
To:	Andrew Morton <akpm@...l.org>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	ext4 <linux-ext4@...r.kernel.org>,
	Will Simoneau <simoneau@....uri.edu>, cmm@...ibm.com
Subject: Re: [PATCH] ext3_getblk should handle HOLE correctly

On Thu, 2006-09-07 at 11:45 -0700, Andrew Morton wrote:
> On Wed, 06 Sep 2006 10:39:06 -0700
> Badari Pulavarty <pbadari@...ibm.com> wrote:
> 
> > Hi Andrew,
> > 
> > Its been reported that ext3_getblk() is not doing the right thing
> > and triggering following WARN():
> > 
> > BUG: warning at fs/ext3/inode.c:1016/ext3_getblk()
> >  <c01c5140> ext3_getblk+0x98/0x2a6  <c03b2806> md_wakeup_thread
> > +0x26/0x2a
> >  <c01c536d> ext3_bread+0x1f/0x88  <c01cedf9> ext3_quota_read+0x136/0x1ae
> >  <c018b683> v1_read_dqblk+0x61/0xac  <c0188f32> dquot_acquire+0xf6/0x107
> >  <c01ceaba> ext3_acquire_dquot+0x46/0x68  <c01897d4> dqget+0x155/0x1e7
> >  <c018a97b> dquot_transfer+0x3e0/0x3e9  <c016fe52> dput+0x23/0x13e
> >  <c01c7986> ext3_setattr+0xc3/0x240  <c0120f66> current_fs_time
> > +0x52/0x6a
> >  <c017320e> notify_change+0x2bd/0x30d  <c0159246> chown_common+0x9c/0xc5
> >  <c02a222c> strncpy_from_user+0x3b/0x68  <c0167fe6> do_path_lookup
> > +0xdf/0x266
> >  <c016841b> __user_walk_fd+0x44/0x5a  <c01592b9> sys_chown+0x4a/0x55
> >  <c015a43c> vfs_write+0xe7/0x13c  <c01695d4> sys_mkdir+0x1f/0x23
> >  <c0102a97> syscall_call+0x7/0xb 
> > 
> > Looking at the code, it looks like its not handle HOLE correctly.
> > It ends up returning -EIO.
> 
> Strange.  The fs should be spewing these warnings all over the place.  For
> some reason this code is hard to trigger.  Why??

I guess - ext3_getblk() mostly used by ext3_bread() and most callers 
to it would be reading already allocated block.

> 
> > -	if (err == 1) {
> > +	/*
> > +	 * ext3_get_blocks_handle() returns number of blocks
> > +	 * mapped. 0 in case of a HOLE.
> > +	 */
> > +	if (err > 0) {
> >  		err = 0;
> > -	} else if (err >= 0) {
> > -		WARN_ON(1);
> > -		err = -EIO;
> >  	}
> 
> That removes the warning if ext3_get_blocks_handle() returned a positive
> number greater than one.  And it looks like we still need debugging support
> in this area.

I am not sure why we need it ? All we care about is one block. If
ext3_get_blocks_handle() returns more than one (which it shouldn't) -
it still be okay. Whats wrong with that ? Just curious ..

May be we should add a WARN() in ext3_get_blocks_handle() when it
returns more than asked for.

Thanks,
Badari

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