Commit 2d873efd authored by Christoph Hellwig's avatar Christoph Hellwig Committed by Carlos Maiolino
Browse files

xfs: flush inodegc before swapon 



Fix the brand new xfstest that tries to swapon on a recently unshared
file and use the chance to document the other bit of magic in this
function.

The big comment is taken from a mailinglist post by Dave Chinner.

Fixes: 5e672cd6 ("xfs: introduce xfs_inodegc_push()")
Signed-off-by: default avatarChristoph Hellwig <hch@lst.de>
Reviewed-by: default avatarDarrick J. Wong <djwong@kernel.org>
Reviewed-by: default avatarDave Chinner <dchinner@redhat.com>
Signed-off-by: default avatarCarlos Maiolino <cem@kernel.org>
parent 3cd6a805

fs/xfs/xfs_aops.c

+34 −1
Original line number Diff line number Diff line
@@ -19,6 +19,7 @@ 
#include "xfs_reflink.h"

#include "xfs_errortag.h"

#include "xfs_error.h"

#include "xfs_icache.h"



struct xfs_writepage_ctx {

	struct iomap_writepage_ctx ctx;
@@ -533,7 +534,39 @@ xfs_vm_swap_activate( 
	struct file			*swap_file,

	sector_t			*span)

{

	sis->bdev = xfs_inode_buftarg(XFS_I(file_inode(swap_file)))->bt_bdev;

	struct xfs_inode		*ip = XFS_I(file_inode(swap_file));



	/*

	 * Swap file activation can race against concurrent shared extent

	 * removal in files that have been cloned.  If this happens,

	 * iomap_swapfile_iter() can fail because it encountered a shared

	 * extent even though an operation is in progress to remove those

	 * shared extents.

	 *

	 * This race becomes problematic when we defer extent removal

	 * operations beyond the end of a syscall (i.e. use async background

	 * processing algorithms).  Users think the extents are no longer

	 * shared, but iomap_swapfile_iter() still sees them as shared

	 * because the refcountbt entries for the extents being removed have

	 * not yet been updated.  Hence the swapon call fails unexpectedly.

	 *

	 * The race condition is currently most obvious from the unlink()

	 * operation as extent removal is deferred until after the last

	 * reference to the inode goes away.  We then process the extent

	 * removal asynchronously, hence triggers the "syscall completed but

	 * work not done" condition mentioned above.  To close this race

	 * window, we need to flush any pending inodegc operations to ensure

	 * they have updated the refcountbt records before we try to map the

	 * swapfile.

	 */

	xfs_inodegc_flush(ip->i_mount);



	/*

	 * Direct the swap code to the correct block device when this file

	 * sits on the RT device.

	 */

	sis->bdev = xfs_inode_buftarg(ip)->bt_bdev;



	return iomap_swapfile_activate(sis, swap_file, span,

			&xfs_read_iomap_ops);

}