Re: loop_set_block_size: loop0 () has still dirty pages (nrpages=2)

From: Karel Zak <kzak@redhat.com>
To: Ingo Franzki <ifranzki@linux.ibm.com>
Cc: Ming Lei <ming.lei@redhat.com>, Jens Axboe <axboe@kernel.dk>,
	linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
	Juergen Christ <jchrist@linux.ibm.com>
Subject: Re: loop_set_block_size: loop0 () has still dirty pages (nrpages=2)
Date: Tue, 15 Jun 2021 10:42:59 +0200	[thread overview]
Message-ID: <20210615084259.yj5pmyjonfqcg7lg@ws.net.home> (raw)
In-Reply-To: <cf3c803f-350e-c365-afac-0a07a9b6cee2@linux.ibm.com>

On Mon, Jun 14, 2021 at 09:35:30AM +0200, Ingo Franzki wrote:
> However, shouldn't then the losetup userspace utility implement some kind of retry logic in case of -EAGAIN ?
> I don't see that in the source of losetup.c nor in loopdev.c in the util-linux package. There is a retry loop in create_loop() in losetup.c retrying loopcxt_setup_device() in case of EBUSY, but not in case of EAGAIN.
> 
> And losetup also hides the original error code and just returns EXIT_FAILURE in case of a failure. So no real good chance for the script that uses losetup to catch that error situation and perform a retry itself.
> 
> Adding Karel Zak (the maintainer of util-linux).
> 
> @Karel Zak: How about adding EAGAIN to the condition for performing a retry? 
> 
> Something like this:
> 
> -		if (errno == EBUSY && !hasdev && ntries < 64) {
> +		if ((errno == EBUSY || errno == EAGAIN) && !hasdev && ntries < 64) {
> 			xusleep(200000);
> 			ntries++;
> 			continue;
> 		}

EAGAIN sounds like the best reason to try it again :-) 

Committed, it will be also available in v2.37.1.

  Karel

-- 
 Karel Zak  <kzak@redhat.com>
 http://karelzak.blogspot.com