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[PATCH v2 0/2] ext4: fallocate insert/collapse range fixes

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  [PATCH v2 0/2] ext4: fallocate insert/collapse range fixes Roman Pen <roman.penyaev@profitbricks.com> - 2017-01-06 21:30 +0100
    [PATCH v2 2/2] ext4: Do not populate extents tree with outdated offsets while shifting extents Roman Pen <roman.penyaev@profitbricks.com> - 2017-01-06 21:30 +0100
      Re: [PATCH v2 2/2] ext4: Do not populate extents tree with outdated  offsets while shifting extents Theodore Ts'o <tytso@mit.edu> - 2017-01-07 22:30 +0100
        Re: [PATCH v2 2/2] ext4: Do not populate extents tree with outdated  offsets while shifting extents Roman Penyaev <roman.penyaev@profitbricks.com> - 2017-01-09 13:40 +0100

#1553081 — [PATCH v2 0/2] ext4: fallocate insert/collapse range fixes

Hi all,

This is the second version of a patchset which targets two nasty bugs in
a logic responsible for shifting extents.  The difference between series
is that in this set the third patch, where I incorrectly tried to optimize
linear search, is skipped.

I ran the 'kvm-xfstests.sh -c 4k -g auto' against b25ead75e7b6 4.10-rc2
with and without my changes.  No regressions were found.

1k configuration was run against latest Linus's mainline.  Also no
regressions were found.

Two patches in a set target two problems, which can be easily reproduced
by the following new xfstest:

  http://www.spinics.net/lists/linux-ext4/msg54965.html

1.  On right shift (insert range) start block is not included in the range
and hole appears at the wrong offset.  The bug can be easily reproduced by
the following test:

    ptr = malloc(4096);
    assert(ptr);

    fd = open("./ext4.file", O_CREAT | O_TRUNC | O_RDWR, 0600);
    assert(fd >= 0);

    rc = fallocate(fd, 0, 0, 8192);
    assert(rc == 0);
    for (i = 0; i < 2048; i++)
            *((unsigned short *)ptr + i) = 0xbeef;
    rc = pwrite(fd, ptr, 4096, 0);
    assert(rc == 4096);
    rc = pwrite(fd, ptr, 4096, 4096);
    assert(rc == 4096);

    for (block = 2; block < 1000; block++) {
            rc = fallocate(fd, FALLOC_FL_INSERT_RANGE, 4096, 4096);
            assert(rc == 0);

            for (i = 0; i < 2048; i++)
                    *((unsigned short *)ptr + i) = block;

            rc = pwrite(fd, ptr, 4096, 4096);
            assert(rc == 4096);
    }

After the test no zero blocks should appear (test always does pwrite() after
fallocate), but zero blocks do exist:

  $ hexdump ./ext4.file | grep '0000 0000'

This bug is targeted by the first patch in the set.

2.  Inside ext4_ext_shift_extents() function ext4_find_extent() is called
without EXT4_EX_NOCACHE flag, which should prevent cache population.  This
leads to outdated offsets in the extents tree and wrong data blocks, which
can be observed doing read().  That is also quite well reproduced by the
test above.

This is fixed by the second patch.

Roman Pen (2):
  ext4: Include forgotten start block on fallocate insert range
  ext4: Do not populate extents tree with outdated offsets while
    shifting extents

 fs/ext4/extents.c | 27 ++++++++++++++++++---------
 1 file changed, 18 insertions(+), 9 deletions(-)

Signed-off-by: Roman Pen <roman.penyaev@profitbricks.com>
Cc: Namjae Jeon <namjae.jeon@samsung.com>
Cc: "Theodore Ts'o" <tytso@mit.edu>
Cc: Andreas Dilger <adilger.kernel@dilger.ca>
Cc: linux-ext4@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
-- 
2.10.2

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#1553083 — [PATCH v2 2/2] ext4: Do not populate extents tree with outdated offsets while shifting extents

Inside ext4_ext_shift_extents() function ext4_find_extent() is called
without EXT4_EX_NOCACHE flag, which should prevent cache population.

This leads to oudated offsets in the extents tree and wrong blocks
afterwards.

Patch fixes the problem providing EXT4_EX_NOCACHE flag for each
ext4_find_extents() call inside ext4_ext_shift_extents function.

Signed-off-by: Roman Pen <roman.penyaev@profitbricks.com>
Cc: Namjae Jeon <namjae.jeon@samsung.com>
Cc: "Theodore Ts'o" <tytso@mit.edu>
Cc: Andreas Dilger <adilger.kernel@dilger.ca>
Cc: linux-ext4@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
---
 fs/ext4/extents.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index 4d3014b5a3f9..2a97dff87b96 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -5334,7 +5334,8 @@ ext4_ext_shift_extents(struct inode *inode, handle_t *handle,
 	ext4_lblk_t stop, *iterator, ex_start, ex_end;
 
 	/* Let path point to the last extent */
-	path = ext4_find_extent(inode, EXT_MAX_BLOCKS - 1, NULL, 0);
+	path = ext4_find_extent(inode, EXT_MAX_BLOCKS - 1, NULL,
+				EXT4_EX_NOCACHE);
 	if (IS_ERR(path))
 		return PTR_ERR(path);
 
@@ -5350,7 +5351,8 @@ ext4_ext_shift_extents(struct inode *inode, handle_t *handle,
 	 * sure the hole is big enough to accommodate the shift.
 	*/
 	if (SHIFT == SHIFT_LEFT) {
-		path = ext4_find_extent(inode, start - 1, &path, 0);
+		path = ext4_find_extent(inode, start - 1, &path,
+					EXT4_EX_NOCACHE);
 		if (IS_ERR(path))
 			return PTR_ERR(path);
 		depth = path->p_depth;
@@ -5388,7 +5390,8 @@ ext4_ext_shift_extents(struct inode *inode, handle_t *handle,
 	 * becomes NULL to indicate the end of the loop.
 	 */
 	while (iterator && start <= stop) {
-		path = ext4_find_extent(inode, *iterator, &path, 0);
+		path = ext4_find_extent(inode, *iterator, &path,
+					EXT4_EX_NOCACHE);
 		if (IS_ERR(path))
 			return PTR_ERR(path);
 		depth = path->p_depth;
-- 
2.10.2

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#1553744 — Re: [PATCH v2 2/2] ext4: Do not populate extents tree with outdated offsets while shifting extents

On Fri, Jan 06, 2017 at 09:26:01PM +0100, Roman Pen wrote:
> Inside ext4_ext_shift_extents() function ext4_find_extent() is called
> without EXT4_EX_NOCACHE flag, which should prevent cache population.
> 
> This leads to oudated offsets in the extents tree and wrong blocks
> afterwards.
> 
> Patch fixes the problem providing EXT4_EX_NOCACHE flag for each
> ext4_find_extents() call inside ext4_ext_shift_extents function.
> 
> Signed-off-by: Roman Pen <roman.penyaev@profitbricks.com>

Thanks, applied.

					- Ted

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#1554275 — Re: [PATCH v2 2/2] ext4: Do not populate extents tree with outdated offsets while shifting extents

On Sat, Jan 7, 2017 at 10:27 PM, Theodore Ts'o <tytso@mit.edu> wrote:
> On Fri, Jan 06, 2017 at 09:26:01PM +0100, Roman Pen wrote:
>> Inside ext4_ext_shift_extents() function ext4_find_extent() is called
>> without EXT4_EX_NOCACHE flag, which should prevent cache population.
>>
>> This leads to oudated offsets in the extents tree and wrong blocks
>> afterwards.
>>
>> Patch fixes the problem providing EXT4_EX_NOCACHE flag for each
>> ext4_find_extents() call inside ext4_ext_shift_extents function.
>>
>> Signed-off-by: Roman Pen <roman.penyaev@profitbricks.com>
>
> Thanks, applied.

Could you please provide with the SHA1 of the patch in your branch?
I want to make an exact reference in a new test of the xfstest which
covers that bug.

--
Roman

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