Re: [PATCH] ext4: Fix data corruption when writing to prealloc area

[Mingming Cao <cmm@us.ibm.com>]

在 2008-07-18五的 10:02 -0700，Mingming Cao写道：
> I tried this patch, with nodelalloc, the kernel did not crash! Previous
> it crashes in a few minutes.
> 
>  but the test did not stop after fill the file by specified 2G size
> 
> 
> I noticed the write() to write to the last fallocate extent(up to 2G)
> returns junk value.
> 
> 
> The testcase I got from Shehjart (who originally reported the problem)
> is  
> 
> http://www.gelato.unsw.edu.au/~shehjart/writefallocate.c
> 

I forget to mention that I modify the test slight to call fallocate()
with default mode (expnd size) instead of keep size.


> command I use to reproduce the problem is 
> 
> ./writefallocate --filesize 2147483648 --wrblksize 65536 --fallocate
> 1048576 --filename /mnt/ext4/a --nounlink
> 
> .............
> offset: 2147024896, written: 65536^M
> offset: 2147090432, written: 65536^M
> offset: 2147155968, written: 65536^M
> offset: 2147221504, written: 65536^M
> offset: 2147287040, written: 65536^M
> offset: 2147352576, written: 65536^M
> offset: 2147418112, written: 65535^M
> offset: 2147483647, written: 18446744073709551615^M
> fallocate offset: 2147483647^M
> offset: 2147483646, written: 18446744073709551615^M
> offset: 2147483645, written: 18446744073709551615^M
> offset: 2147483644, written: 18446744073709551615^M
> offset: 2147483643, written: 18446744073709551615^M
> offset: 2147483642, written: 18446744073709551615^M
> offset: 2147483641, written: 18446744073709551615^M
> offset: 2147483640, written: 18446744073709551615^M
> 
> 
> Appearently the test has fallocate/fill the 2G file, but since the last
> write() returns 18446744073709551615, the offset is decreased, cause the
> test continue with a break,  and writes to wrong offset
> 
> 
> 
> 
> 在 2008-07-18五的 18:47 +0530，Aneesh Kumar K.V写道：
> > We need to recalucate the path information on extent insert
> > even if depth doesn't change.
> > 
> > Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
> > ---
> >  fs/ext4/extents.c |   41 +++++++++++++++++++++++------------------
> >  1 files changed, 23 insertions(+), 18 deletions(-)
> > 
> > diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
> > index 7bdaeec..9c8541e 100644
> > --- a/fs/ext4/extents.c
> > +++ b/fs/ext4/extents.c
> > @@ -2462,7 +2462,10 @@ static int ext4_ext_convert_to_initialized(handle_t *handle,
> >  		unsigned int newdepth;
> >  		/* If extent has less than EXT4_EXT_ZERO_LEN zerout directly */
> >  		if (allocated <= EXT4_EXT_ZERO_LEN) {
> > -			/* Mark first half uninitialized.
> > +			/*
> > +			 * iblock == ee_block is handled by the zerouout
> > +			 * at the beginning.
> > +			 * Mark first half uninitialized.
> >  			 * Mark second half initialized and zero out the
> >  			 * initialized extent
> >  			 */
> > @@ -2485,7 +2488,7 @@ static int ext4_ext_convert_to_initialized(handle_t *handle,
> >  				ex->ee_len   = orig_ex.ee_len;
> >  				ext4_ext_store_pblock(ex, ext_pblock(&orig_ex));
> >  				ext4_ext_dirty(handle, inode, path + depth);
> > -				/* zeroed the full extent */
> > +				/* blocks available from iblock */
> >  				return allocated;
> > 
> >  			} else if (err)
> > @@ -2513,6 +2516,7 @@ static int ext4_ext_convert_to_initialized(handle_t *handle,
> >  					err = PTR_ERR(path);
> >  					return err;
> >  				}
> > +				/* get the second half extent details */
> >  				ex = path[depth].p_ext;
> >  				err = ext4_ext_get_access(handle, inode,
> >  								path + depth);
> > @@ -2542,6 +2546,7 @@ static int ext4_ext_convert_to_initialized(handle_t *handle,
> >  			ext4_ext_store_pblock(ex, ext_pblock(&orig_ex));
> >  			ext4_ext_dirty(handle, inode, path + depth);
> >  			/* zeroed the full extent */
> > +			/* blocks available from iblock */
> >  			return allocated;
> > 
> >  		} else if (err)
> > @@ -2557,23 +2562,22 @@ static int ext4_ext_convert_to_initialized(handle_t *handle,
> >  		 */
> >  		orig_ex.ee_len = cpu_to_le16(ee_len -
> >  						ext4_ext_get_actual_len(ex3));
> > -		if (newdepth != depth) {
> > -			depth = newdepth;
> > -			ext4_ext_drop_refs(path);
> > -			path = ext4_ext_find_extent(inode, iblock, path);
> > -			if (IS_ERR(path)) {
> > -				err = PTR_ERR(path);
> > -				goto out;
> > -			}
> > -			eh = path[depth].p_hdr;
> > -			ex = path[depth].p_ext;
> > -			if (ex2 != &newex)
> > -				ex2 = ex;
> > -
> > -			err = ext4_ext_get_access(handle, inode, path + depth);
> > -			if (err)
> > -				goto out;
> > +		depth = newdepth;
> > +		ext4_ext_drop_refs(path);
> > +		path = ext4_ext_find_extent(inode, iblock, path);
> > +		if (IS_ERR(path)) {
> > +			err = PTR_ERR(path);
> > +			goto out;
> >  		}
> > +		eh = path[depth].p_hdr;
> > +		ex = path[depth].p_ext;
> > +		if (ex2 != &newex)
> > +			ex2 = ex;
> > +
> > +		err = ext4_ext_get_access(handle, inode, path + depth);
> > +		if (err)
> > +			goto out;
> > +
> >  		allocated = max_blocks;
> > 
> >  		/* If extent has less than EXT4_EXT_ZERO_LEN and we are trying
> > @@ -2591,6 +2595,7 @@ static int ext4_ext_convert_to_initialized(handle_t *handle,
> >  			ext4_ext_store_pblock(ex, ext_pblock(&orig_ex));
> >  			ext4_ext_dirty(handle, inode, path + depth);
> >  			/* zero out the first half */
> > +			/* blocks available from iblock */
> >  			return allocated;
> >  		}
> >  	}
> 
> --
> To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html