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xfs: xfs_check_page_type buffer checks need help

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xfs_aops_discard_page() was introduced in the following commit:

  xfs: truncate delalloc extents when IO fails in writeback

... to clean up left over delalloc ranges after I/O failure in
->writepage(). generic/224 tests for this scenario and occasionally
reproduces panics on sub-4k blocksize filesystems.

The cause of this is failure to clean up the delalloc range on a
page where the first buffer does not match one of the expected
states of xfs_check_page_type(). If a buffer is not unwritten,
delayed or dirty&mapped, xfs_check_page_type() stops and
immediately returns 0.

The stress test of generic/224 creates a scenario where the first
several buffers of a page with delayed buffers are mapped & uptodate
and some subsequent buffer is delayed. If the ->writepage() happens
to fail for this page, xfs_aops_discard_page() incorrectly skips
the entire page.

This then causes later failures either when direct IO maps the range
and finds the stale delayed buffer, or we evict the inode and find
that the inode still has a delayed block reservation accounted to
it.

We can easily fix this xfs_aops_discard_page() failure by making
xfs_check_page_type() check all buffers, but this breaks
xfs_convert_page() more than it is already broken. Indeed,
xfs_convert_page() wants xfs_check_page_type() to tell it if the
first buffers on the pages are of a type that can be aggregated into
the contiguous IO that is already being built.

xfs_convert_page() should not be writing random buffers out of a
page, but the current behaviour will cause it to do so if there are
buffers that don't match the current specification on the page.
Hence for xfs_convert_page() we need to:

	a) return "not ok" if the first buffer on the page does not
	match the specification provided to we don't write anything;
	and
	b) abort it's buffer-add-to-io loop the moment we come
	across a buffer that does not match the specification.

Hence we need to fix both xfs_check_page_type() and
xfs_convert_page() to work correctly with pages that have mixed
buffer types, whilst allowing xfs_aops_discard_page() to scan all
buffers on the page for a type match.

Reported-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Dave Chinner <david@fromorbit.com>
This commit is contained in:
Dave Chinner 2014-03-07 16:19:14 +11:00 committed by Dave Chinner
parent e480a72397
commit a49935f200
1 changed files with 50 additions and 31 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

81
fs/xfs/xfs_aops.c
View file

@ -632,38 +632,46 @@ xfs_map_at_offset(
}
/*
* Test if a given page is suitable for writing as part of an unwritten
* or delayed allocate extent.
* Test if a given page contains at least one buffer of a given @type.
* If @check_all_buffers is true, then we walk all the buffers in the page to
* try to find one of the type passed in. If it is not set, then the caller only
* needs to check the first buffer on the page for a match.
*/
STATIC int
STATIC bool
xfs_check_page_type(
struct page *page,
unsigned int type)
unsigned int type,
bool check_all_buffers)
{
struct buffer_head *bh;
struct buffer_head *head;
if (PageWriteback(page))
return 0;
return false;
if (!page->mapping)
return false;
if (!page_has_buffers(page))
return false;
if (page->mapping && page_has_buffers(page)) {
struct buffer_head *bh, *head;
int acceptable = 0;
bh = head = page_buffers(page);
do {
if (buffer_unwritten(bh)) {
if (type == XFS_IO_UNWRITTEN)
return true;
} else if (buffer_delay(bh)) {
if (type == XFS_IO_DELALLOC);
return true;
} else if (buffer_dirty(bh) && buffer_mapped(bh)) {
if (type == XFS_IO_OVERWRITE);
return true;
}
bh = head = page_buffers(page);
do {
if (buffer_unwritten(bh))
acceptable += (type == XFS_IO_UNWRITTEN);
else if (buffer_delay(bh))
acceptable += (type == XFS_IO_DELALLOC);
else if (buffer_dirty(bh) && buffer_mapped(bh))
acceptable += (type == XFS_IO_OVERWRITE);
else
break;
} while ((bh = bh->b_this_page) != head);
/* If we are only checking the first buffer, we are done now. */
if (!check_all_buffers)
break;
} while ((bh = bh->b_this_page) != head);
if (acceptable)
return 1;
}
return 0;
return false;
}
/*
@ -697,7 +705,7 @@ xfs_convert_page(
goto fail_unlock_page;
if (page->mapping != inode->i_mapping)
goto fail_unlock_page;
if (!xfs_check_page_type(page, (*ioendp)->io_type))
if (!xfs_check_page_type(page, (*ioendp)->io_type, false))
goto fail_unlock_page;
/*
@ -742,6 +750,15 @@ xfs_convert_page(
p_offset = p_offset ? roundup(p_offset, len) : PAGE_CACHE_SIZE;
page_dirty = p_offset / len;
/*
* The moment we find a buffer that doesn't match our current type
* specification or can't be written, abort the loop and start
* writeback. As per the above xfs_imap_valid() check, only
* xfs_vm_writepage() can handle partial page writeback fully - we are
* limited here to the buffers that are contiguous with the current
* ioend, and hence a buffer we can't write breaks that contiguity and
* we have to defer the rest of the IO to xfs_vm_writepage().
*/
bh = head = page_buffers(page);
do {
if (offset >= end_offset)
@ -750,7 +767,7 @@ xfs_convert_page(
uptodate = 0;
if (!(PageUptodate(page) || buffer_uptodate(bh))) {
done = 1;
continue;
break;
}
if (buffer_unwritten(bh) || buffer_delay(bh) ||
@ -762,10 +779,11 @@ xfs_convert_page(
else
type = XFS_IO_OVERWRITE;
if (!xfs_imap_valid(inode, imap, offset)) {
done = 1;
continue;
}
/*
* imap should always be valid because of the above
* partial page end_offset check on the imap.
*/
ASSERT(xfs_imap_valid(inode, imap, offset));
lock_buffer(bh);
if (type != XFS_IO_OVERWRITE)
@ -777,6 +795,7 @@ xfs_convert_page(
count++;
} else {
done = 1;
break;
}
} while (offset += len, (bh = bh->b_this_page) != head);
@ -868,7 +887,7 @@ xfs_aops_discard_page(
struct buffer_head *bh, *head;
loff_t offset = page_offset(page);
if (!xfs_check_page_type(page, XFS_IO_DELALLOC))
if (!xfs_check_page_type(page, XFS_IO_DELALLOC, true))
goto out_invalidate;
if (XFS_FORCED_SHUTDOWN(ip->i_mount))