Re: [PATCH v2 3/4] ext4: add inode to orphan list before extent conversion

[sashiko-bot@kernel.org]

> From: Zhang Yi <yi.zhang@huawei.com>
> 
> ext4_alloc_file_blocks() zeroes the blocks it has just allocated and
> converts their unwritten extents in a handle started with
> ext4_chunk_trans_blocks(), which reserves credits for a single extent.
> The range is allocated with ext4_map_blocks() first and converted
> afterwards, and only the unwritten extent conversion which runs on I/O
> completion can modify the extent tree of that range in between, since
> this path holds i_rwsem. If such a conversion converts part of the
> range first, it splits the extent, and converting the whole range then
> needs more credits than the handle has reserved.
> 
> Before commit 10660a0ca7ed ("ext4: rework handle credit accounting for
> unwritten extent conversion"), this race condition led to insufficient
> credits, which made the conversion fail with -ENOSPC in the middle of
> the range. After it, ext4_convert_unwritten_extents() can extend or
> restart the transaction. Restarting commits everything modified so
> far, so the extents converted by the first iterations reach the disk
> before this function adds the inode to the orphan list. A crash in
> between leaves written extents beyond i_disksize on disk with the
> inode not on the orphan list, which fsck complains about.
> 
> Add the inode to the orphan list before the conversion instead and keep
> it there until i_disksize has caught up. A restart then commits the
> orphan entry together with the extents converted so far, and the entry
> is only removed by the transaction which raises i_disksize and i_size.
> 
> Fixes: 10660a0ca7ed ("ext4: rework handle credit accounting for unwritten extent conversion")
> Fixes: f7237a775c8f ("ext4: protect WRITE_ZEROES written extents with orphan list")
> Signed-off-by: Zhang Yi <yi.zhang@huawei.com>

Sashiko has reviewed this patch and found no issues.

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