On Tue, Jul 2, 2024 at 11:18 PM Benjamin Marzinski <bmarzins@xxxxxxxxxx> wrote:
>
> When handling an IO request, MD checks if a reshape is currently
> happening, and if so, where the IO sector is in relation to the reshape
> progress. MD uses conf->reshape_progress for both of these tasks. When
> the reshape finishes, conf->reshape_progress is set to MaxSector. If
> this occurs after MD checks if the reshape is currently happening but
> before it calls ahead_of_reshape(), then ahead_of_reshape() will end up
> comparing the IO sector against MaxSector. During a backwards reshape,
> this will make MD think the IO sector is in the area not yet reshaped,
> causing it to use the previous configuration, and map the IO to the
> sector where that data was before the reshape.
>
> This bug can be triggered by running the lvm2
> lvconvert-raid-reshape-linear_to_raid6-single-type.sh test in a loop,
> although it's very hard to reproduce.
>
> Fix this by factoring the code that checks where the IO sector is in
> relation to the reshape out to a helper called get_reshape_loc(),
> which reads reshape_progress and reshape_safe while holding the
> device_lock, and then rechecks if the reshape has finished before
> calling ahead_of_reshape with the saved values.
>
> Also use the helper during the REQ_NOWAIT check to see if the location
> is inside of the reshape region.
>
> Fixes: fef9c61fdfabf ("md/raid5: change reshape-progress measurement to cope with reshaping backwards.")
> Signed-off-by: Benjamin Marzinski <bmarzins@xxxxxxxxxx>
Applied to md-6.11. Thanks!
Song
