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Before I look in the details of the patches, I would like make a comment below. > Reproducing the race needs an IO that can be held at the target for > longer than the host's io_timeout without being failed. The first three > patches give miniublk that ability, since there was previously no way to > talk to a running ublk server at all: > > 1/5 adds a loopback UDP control channel to the daemon, served by a > detached thread, one reply datagram per request > 2/5 adds an INJECT_DELAY command which delays a given number of reads > or writes as an io_uring timeout on the queue's own ring > 3/5 exposes it as "miniublk inject", which returns only once the > daemon has armed the delay, so a test can start IO immediately > without racing it It is interesting to implement the delay feature to miniublk, and use it as the testing tool. But I'm not sure if this is the best approach because of two points. First, scsi_debug has jdelay and ndelay options. I wonder if this existing feature can fulfill the requirements of the new test case. Second, when rublk [*] is available in the PATH of the test system, blktests detect it and use it instead of miniublk. I guess the added delay feature is not available in rublk, and the test case won't work well. What do you think of these points?