linux-kernel - Re: [PATCH 4/4] ublk: improve handling of saturated queues when ublk server exits

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Message-ID: <Z+RN+CPnWO69aJD5@dev-ushankar.dev.purestorage.com>
Date: Wed, 26 Mar 2025 12:56:56 -0600
From: Uday Shankar <ushankar@...estorage.com>
To: Ming Lei <ming.lei@...hat.com>
Cc: Shuah Khan <shuah@...nel.org>, Jens Axboe <axboe@...nel.dk>,
	linux-block@...r.kernel.org, linux-kselftest@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/4] ublk: improve handling of saturated queues when ublk
 server exits

On Wed, Mar 26, 2025 at 11:54:16AM -0600, Uday Shankar wrote:
> > ublk_abort_requests() should be called only in case of queue dying,
> > since ublk server may open & close the char device multiple times.
> 
> Sure that is technically possible, however is any real ublk server doing
> this? Seems like a strange thing to do, and seems reasonable for the
> driver to transition the device to the nosrv state (dead or recovery,
> depending on flags) when the char device is closed, since in this case,
> no one can be handling I/O anymore.

I see ublksrv itself is doing this :(

/* Wait until ublk device is setup by udev */
static void ublksrv_check_dev(const struct ublksrv_ctrl_dev_info *info)
{
	unsigned int max_time = 1000000, wait = 0;
	char buf[64];

	snprintf(buf, 64, "%s%d", "/dev/ublkc", info->dev_id);

	while (wait < max_time) {
		int fd = open(buf, O_RDWR);

		if (fd > 0) {
			close(fd);
			break;
		}

		usleep(100000);
		wait += 100000;
	}
}

This seems related to some failures in ublksrv tests