Re: [Devel] [PATCH hci-8.1 v2 0/3] dm-qcow2: fix merges not stopping the users of the images they change

[Konstantin Khorenko <khorenko@virtuozzo.com>]

I won't apply this version, please send v2 with the changes below.

On 11/3/26 10:08, Denis V. Lunev wrote:
> Denis V. Lunev (3):
>   dm-qcow2: fix a failed refcount table relocation leaking md pages
>   dm-qcow2: fix backward merge of an inner image racing its reads
>   dm-qcow2: fix SEEK_HOLE/SEEK_DATA using an image freed by a merge

What to change for v2:

1. Patch 1, code: after a successful header write, the error gotos
   must not free the new md pages. Send them to a label after the free
   loop that only returns -EIO, and update the "Note for a future
   reader" to match.
2. Patch 2, code comment: write "no guest writes" instead of "no
   writes".
3. Patch 2, commit message: say that guest I/O to the top image is now
   paused for the inflight ref switch when a merge of an inner image
   starts or stops.
4. Patch 3, commit message: say that merge_backward complete now waits
   for a running seek while it holds ctl_mutex.
5. Cover letter: fix the bullet on patch 2 quoted below.

Separate patches, not needed for v2:

6. relocate_refcount_table(): the refcount group of the new reftable
   gets no refblock when the table fills that whole group.
7. qcow2_llseek_hole(): a seek waits forever when one of its md page
   reads fails.

The details are in the replies to each patch.

> - a backward merge of an inner image pauses that image, while reads
>   enter through the top one. A read reaching the inner image as the
>   merge starts oopses on a NULL qio->ext (patch 2);

Item 5: before the series the start of an inner merge paused nothing,
only the stop paused the inner image. Say that the start paused nothing.

-- 
Konstantin Khorenko,
Virtuozzo Linux Kernel Team

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