[Devel] [PATCH hci-8.1 v2 1/3] dm-ploop: fix flip_upper_deltas returning with two md_locks held

[no-reply at sashiko.virtuozzo.com]

> From: Denis V. Lunev <den at openvz.org>
> 
> ploop_check_delta_before_flip() takes the md_lock of a live BAT page
> and of the matching page of the lower delta before it compares them.
> When it finds a cluster both deltas map, it jumps to unmap past both
> unlocks: the cmd returns -EEXIST with the locks held and interrupts
> disabled, after freeing the page of the lower delta with its lock still
> taken. dmsetup comes back to userspace in atomic context, and the next
> pio touching that BAT page spins on its md_lock for good, a hard
> lockup.
> 
> A flip_upper_deltas message on a chain where the top delta overwrote a
> cluster of the lower one gets there. The ploop library does not: its
> reverse merge clears those entries in the lower delta with the device
> suspended before it flips.
> 
> Leave the scan only after both locks are dropped.
> 
> Fixes: 0d4b4d0a20a9 ("dm-ploop: introduce per-md page locking")
> https://virtuozzo.atlassian.net/browse/VSTOR-153445
> Feature: dm-ploop: ploop target driver
> Reviewed-by: Andrey Zhadchenko <andrey.zhadchenko at virtuozzo.com>
> Reviewed-by: Konstantin Khorenko <khorenko at virtuozzo.com>
> Signed-off-by: Denis V. Lunev <den at openvz.org>

Sashiko has reviewed this patch and found no issues. It looks great!

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Sashiko AI review · https://sashiko.vzint.dev/#/patchset/20261105145749.2643035-1-den@openvz.org?part=1