https://bugzilla.kernel.org/show_bug.cgi?id=212337 Luis Chamberlain (mcgrof@xxxxxxxxxx) changed: What |Removed |Added ---------------------------------------------------------------------------- Status|RESOLVED |REOPENED Resolution|WILL_NOT_FIX |--- --- Comment #13 from Luis Chamberlain (mcgrof@xxxxxxxxxx) --- (In reply to d gilbert from comment #12) > On 2021-03-22 12:23 p.m., bugzilla-daemon@xxxxxxxxxxxxxxxxxxx wrote: > > https://bugzilla.kernel.org/show_bug.cgi?id=212337 > > > > --- Comment #9 from Luis Chamberlain (mcgrof@xxxxxxxxxx) --- > > (In reply to d gilbert from comment #8) > > > >>>> The scsi_debug module option that is already in place is: > >>>> tur_ms_to_ready: TEST UNIT READY millisecs before initial good > status > >>>> (def=0) > >> > >> You asked how it works, try: > >> modprobe scsi_debug tur_ms_to_ready=20000 > >> > > > > That does not resolve the rmmod race against insmod: > > > > scsi host2: scsi_debug: version 0190 [20200710] > > [ 42.213400] dev_size_mb=8, opts=0x0, submit_queues=1, statistics=0 > > [ 42.217527] scsi 2:0:0:0: Direct-Access Linux scsi_debug > 0190 > > PQ: 0 ANSI: 7 > > [ 42.223346] scsi 2:0:0:0: Attached scsi generic sg0 type 0 > > [ 42.282195] scsi host2: scsi_debug: version 0190 [20200710] > > [ 42.282195] dev_size_mb=8, opts=0x0, submit_queues=1, statistics=0 > > [ 42.288169] scsi 2:0:0:0: Direct-Access Linux scsi_debug > 0190 > > PQ: 0 ANSI: 7 > > [ 42.292122] sd 2:0:0:0: Attached scsi generic sg0 type 0 > > [ 42.292244] sd 2:0:0:0: Power-on or device reset occurred > > [ 42.302288] sd 2:0:0:0: [sda] Spinning up disk... > > > > Then we wait... > > > > [ 44.308213] ...................ready > > [ 62.748919] sd 2:0:0:0: [sda] 16384 512-byte logical blocks: (8.39 > MB/8.00 > > MiB) > > [ 62.754265] sd 2:0:0:0: [sda] Write Protect is off > > [ 62.763253] sd 2:0:0:0: [sda] Write cache: enabled, read cache: enabled, > > supports DPO and FUA > > [ 62.776965] sd 2:0:0:0: [sda] Optimal transfer size 524288 bytes > > [ 62.883817] sd 2:0:0:0: [sda] Attached SCSI disk > > > > And then rmmod still fails. > > > > Just to explain a bit more about tur_ms_to_ready, that does not effect SCSI > commands like REPORT LUNS, INQUIRY and REQUEST SENSE, but does slow down all > "media access" commands including TEST UNIT READY (TUR) and READ CAPACITY. So > if you watch what is happening with 'lsscsi -s' the device (LUN) will appear > almost immediately but its size will be "-" due to the fact that READ > CAPACITY (or TUR before it) is waiting for tur_ms_to_ready to elapse. After > that the size (for disks) will be shown by 'lsscsi -s'. > > > When you say 'rmmod still fails' do you mean it refuses to remove the module > because the device is busy? Yes. The refcnt must be 1 for rmmod to work. If it is not it will fail. > If is busy, where is the race?. What precisely > would you like to happen? What does a real SCSI HBA do? That's the thing, the trace on comment #1 does not exactly show who to blame, but there seems to be only two possibilities: systemd and multipath. Regardless what is clearer is that once the device is exposed we *cannot* block userspace from poking at the device. The best we can do, is udevadm settle, however that still does not guarantee userspace things like multipath won't try to poke. > Is there any way that a driver can detect that rmmod has been called and > rejected? Yes! try_module_get() would fail if rmmod was kicked off. > If not, we could add a "shutdown" writable attribute in > /sys/bus/pseudo/drivers/scsi_debug/ . Then if a large number of pseudo > devices is being built due to the modprobe invocation, the driver can go > into reverse by checking that attribute before it adds another host > (target or LUN?). After shutdown, the driver is still active, just with > no hosts, and thus no LUNs. A more accurate name would be rm_all_hosts . This may work actually, and so new users who would want to avoid this race would have to issue this call prior to rmmod. That would remove the possibility of a race. Let me know if you have a patch I can test. Putting this as re-opened. -- You may reply to this email to add a comment. You are receiving this mail because: You are watching the assignee of the bug.
