Re: [Devel] [PATCH hci-8.1 3/4] dm-ploop: wait for the ploop_allocator() thread before changing deltas[]

[no-reply@sashiko.virtuozzo.com]

> From: Denis V. Lunev <den@openvz.org>
> 
> An allocating pio requests the preallocation of the top delta ahead of
> itself and does not wait when its cluster already fits, so the
> allocator can still be working when submission is suspended or the
> device is dm suspended. It looks up the top delta without a lock and
> keeps the pointer and the file across its truncate or fallocate, while
> a cmd rewrites deltas[] under neither of its locks:
> 
> - merge and notify_merged_backward move the top delta one slot down and
>   zero the old slot. The allocator then reads a zero file_size from it
>   and truncates the live top image down to the preallocation size, or
>   reads a NULL file and oopses;
> 
> - flip_upper_deltas swaps the two upper slots of a dm suspended device.
>   The allocator computes the new length from the size of the delta now
>   on top and truncates the old top one, now holding data below it, to
>   that length.
> 
> Wait for the allocator to finish in ploop_suspend_submitting_pios()
> after the inflight pios are gone, and in ploop_postsuspend() before
> the device is marked suspended, which is what the flip checks. No pio
> can request a new preallocation at either point. Wake the waiters with
> wake_up(), as the one in ploop_postsuspend() sleeps uninterruptibly.
> 
> Fixes: cf489cf22cd5 ("dm-ploop: make filespace preallocations async")
> Reported-by: Konstantin Khorenko <khorenko@virtuozzo.com>
> https://virtuozzo.atlassian.net/browse/VSTOR-152984
> Feature: dm-ploop: ploop target driver
> Signed-off-by: Denis V. Lunev <den@openvz.org>

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

-- 
Sashiko AI review · https://sashiko.vzint.dev/#/patchset/20261103083642.130885-1-den@openvz.org?part=3


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