xfs: delayed alloc blocks beyond EOF are valid after writeback (309c8480) · Commits · 戴 / test

There is an assumption in the parts of XFS that flushing a dirty file will make all the delayed allocation blocks disappear from an inode. That is, that after calling xfs_flush_pages() then ip->i_delayed_blks will be zero. This is an invalid assumption as we may have specualtive preallocation beyond EOF and they are recorded in ip->i_delayed_blks. A flush of the dirty pages of an inode will not change the state of these blocks beyond EOF, so a non-zero deeelalloc block count after a flush is valid. The bmap code has an invalid ASSERT() that needs to be removed, and the swapext code has a bug in that while it swaps the data forks around, it fails to swap the i_delayed_blks counter associated with the fork and hence can get the block accounting wrong. Signed-off-by:

Dave Chinner <dchinner@redhat.com> Reviewed-by:

Christoph Hellwig <hch@lst.de>

fs/xfs/xfs_bmap.c

+7 −2

Original line number	Diff line number	Diff line
		@@ -5471,8 +5471,13 @@ xfs_getbmap(
		if (error)
		goto out_unlock_iolock;
		}

		ASSERT(ip->i_delayed_blks == 0);
		/*
		* even after flushing the inode, there can still be delalloc
		* blocks on the inode beyond EOF due to speculative
		* preallocation. These are not removed until the release
		* function is called or the inode is inactivated. Hence we
		* cannot assert here that ip->i_delayed_blks == 0.
		*/
		}

		lock = xfs_ilock_map_shared(ip);

fs/xfs/xfs_dfrag.c

+13 −0

Original line number	Diff line number	Diff line
		@@ -377,6 +377,19 @@ xfs_swap_extents(
		ip->i_d.di_format = tip->i_d.di_format;
		tip->i_d.di_format = tmp;

		/*
		* The extents in the source inode could still contain speculative
		* preallocation beyond EOF (e.g. the file is open but not modified
		* while defrag is in progress). In that case, we need to copy over the
		* number of delalloc blocks the data fork in the source inode is
		* tracking beyond EOF so that when the fork is truncated away when the
		* temporary inode is unlinked we don't underrun the i_delayed_blks
		* counter on that inode.
		*/
		ASSERT(tip->i_delayed_blks == 0);
		tip->i_delayed_blks = ip->i_delayed_blks;
		ip->i_delayed_blks = 0;

		ilf_fields = XFS_ILOG_CORE;

		switch(ip->i_d.di_format) {

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