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xfs: Fix missed holes in SEEK_HOLE implementation 

XFS SEEK_HOLE implementation could miss a hole in an unwritten extent as
can be seen by the following command:

xfs_io -c "falloc 0 256k" -c "pwrite 0 56k" -c "pwrite 128k 8k"
       -c "seek -h 0" file
wrote 57344/57344 bytes at offset 0
56 KiB, 14 ops; 0.0000 sec (49.312 MiB/sec and 12623.9856 ops/sec)
wrote 8192/8192 bytes at offset 131072
8 KiB, 2 ops; 0.0000 sec (70.383 MiB/sec and 18018.0180 ops/sec)
Whence	Result
HOLE	139264

Where we can see that hole at offset 56k was just ignored by SEEK_HOLE
implementation. The bug is in xfs_find_get_desired_pgoff() which does
not properly detect the case when pages are not contiguous.

Fix the problem by properly detecting when found page has larger offset
than expected.

CC: stable@vger.kernel.org
Fixes: d126d43f63
Signed-off-by: Jan Kara <jack@suse.cz>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
This commit is contained in:
Jan Kara 2017-05-18 16:36:22 -07:00 committed by Darrick J. Wong
parent 8affebe16d
commit 5375023ae1
1 changed files with 9 additions and 20 deletions
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29
fs/xfs/xfs_file.c
View File

@ -1076,17 +1076,6 @@ xfs_find_get_desired_pgoff(
break;
}
/*
* At lease we found one page. If this is the first time we
* step into the loop, and if the first page index offset is
* greater than the given search offset, a hole was found.
*/
if (type == HOLE_OFF && lastoff == startoff &&
lastoff < page_offset(pvec.pages[0])) {
found = true;
break;
}
for (i = 0; i < nr_pages; i++) {
struct page *page = pvec.pages[i];
loff_t b_offset;
@ -1098,18 +1087,18 @@ xfs_find_get_desired_pgoff(
* file mapping. However, page->index will not change
* because we have a reference on the page.
*
* Searching done if the page index is out of range.
* If the current offset is not reaches the end of
* the specified search range, there should be a hole
* between them.
* If current page offset is beyond where we've ended,
* we've found a hole.
*/
if (page->index > end) {
if (type == HOLE_OFF && lastoff < endoff) {
*offset = lastoff;
found = true;
}
if (type == HOLE_OFF && lastoff < endoff &&
lastoff < page_offset(pvec.pages[i])) {
found = true;
*offset = lastoff;
goto out;
}
/* Searching done if the page index is out of range. */
if (page->index > end)
goto out;
lock_page(page);
/*