Re: [PULL 3/5] block/reqlist: allow adding overlapping requests

[Michael Tokarev]

30.09.2024 11:43, Vladimir Sementsov-Ogievskiy wrote:
> From: Fiona Ebner <f.ebner@proxmox.com>
>
> Allow overlapping request by removing the assert that made it
> impossible. There are only two callers:
>
> 1. block_copy_task_create()
>
> It already asserts the very same condition before calling
> reqlist_init_req().
>
> 2. cbw_snapshot_read_lock()
>
> There is no need to have read requests be non-overlapping in
> copy-before-write when used for snapshot-access. In fact, there was no
> protection against two callers of cbw_snapshot_read_lock() calling
> reqlist_init_req() with overlapping ranges and this could lead to an
> assertion failure [1].
>
> In particular, with the reproducer script below [0], two
> cbw_co_snapshot_block_status() callers could race, with the second
> calling reqlist_init_req() before the first one finishes and removes
> its conflicting request.

Hm.  This one applies to 7.2 too (current oldest stable series), with
the description above matching what the code is doing.

I picked it up for up to 7.2.  Please let me know if this shouldn't be
done :)

Thanks,

/mjt