s390/dasd: prevent double format of tracks for ESE devices

For ESE devices we get an error for write operations on an unformatted
track. Afterwards the track will be formatted and the IO operation
restarted.
When using alias devices a track might be accessed by multiple requests
simultaneously and there is a race window that a track gets formatted
twice resulting in data loss.

Prevent this by remembering the amount of formatted tracks when starting
a request and comparing this number before actually formatting a track
on the fly. If the number has changed there is a chance that the current
track was finally formatted in between. As a result do not format the
track and restart the current IO to check.

The number of formatted tracks does not match the overall number of
formatted tracks on the device and it might wrap around but this is no
problem. It is only needed to recognize that a track has been formatted at
all in between.

Fixes: 5e2b17e712cf ("s390/dasd: Add dynamic formatting support for ESE volumes")
Cc: stable@vger.kernel.org # 5.3+
Signed-off-by: Stefan Haberland <sth@linux.ibm.com>
Reviewed-by: Jan Hoeppner <hoeppner@linux.ibm.com>
Link: https://lore.kernel.org/r/20220505141733.1989450-3-sth@linux.ibm.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 7 insertions, 0 deletions

diff --git a/drivers/s390/block/dasd.c b/drivers/s390/block/dasd.c
index 76d13c5ff205..d62a4c673962 100644
--- a/drivers/s390/block/dasd.c
+++ b/drivers/s390/block/dasd.c
@@ -1422,6 +1422,13 @@ int dasd_start_IO(struct dasd_ccw_req *cqr)
 		if (!cqr->lpm)
 			cqr->lpm = dasd_path_get_opm(device);
 	}
+	/*
+	 * remember the amount of formatted tracks to prevent double format on
+	 * ESE devices
+	 */
+	if (cqr->block)
+		cqr->trkcount = atomic_read(&cqr->block->trkcount);
+
 	if (cqr->cpmode == 1) {
 		rc = ccw_device_tm_start(device->cdev, cqr->cpaddr,
 					 (long) cqr, cqr->lpm);