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Date:   Tue, 27 Oct 2020 19:49:26 +0100
From:   Petr Vorel <pvorel@suse.cz>
To:     linux-block@vger.kernel.org
Cc:     Martijn Coenen <maco@android.com>, Christoph Hellwig <hch@lst.de>,
        Jens Axboe <axboe@kernel.dk>, ltp@lists.linux.it,
        Cyril Hrubis <chrubis@suse.cz>
Subject: Ocassional dropping of uevent of loop device (possible race)
Message-ID: <20201027184926.GA24024@dell5510>
Reply-To: Petr Vorel <pvorel@suse.cz>
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Hi

commit 716ad0986cbd ("loop: Switch to set_capacity_revalidate_and_notify()")
from v5.8-rc1 caused occasional dropping of uevent of attached or detached loop
device (not sure which one). The only difference is that
set_capacity_revalidate_and_notify() has condition:
if (capacity != size && capacity != 0 && size != 0)
thus notification is not triggered here but in a different part of code.

It was found with LTP test uevent01 [1]:

# i=0; while true; do i=$((i+1)); echo "== $i =="; rmmod -f loop; ./uevent01 || break; done

It looks to be a race. Usually ~ 10 loops is enough.

Kind regards,
Petr