On 29.07.20 17:40, Alan Stern wrote: > On Wed, Jul 29, 2020 at 07:53:52AM -0700, James Bottomley wrote: >> On Wed, 2020-07-29 at 07:46 -0700, James Bottomley wrote: >>> On Wed, 2020-07-29 at 10:32 -0400, Alan Stern wrote: >>>> On Wed, Jul 29, 2020 at 04:12:22PM +0200, Martin Kepplinger wrote: >>>>> On 28.07.20 22:02, Alan Stern wrote: >>>>>> On Tue, Jul 28, 2020 at 09:02:44AM +0200, Martin Kepplinger >>>>>> wrote: >>>>>>> Hi Alan, >>>>>>> >>>>>>> Any API cleanup is of course welcome. I just wanted to remind >>>>>>> you that the underlying problem: broken block device runtime >>>>>>> pm. Your initial proposed fix "almost" did it and mounting >>>>>>> works but during file access, it still just looks like a >>>>>>> runtime_resume is missing somewhere. >>>>>> >>>>>> Well, I have tested that proposed fix several times, and on my >>>>>> system it's working perfectly. When I stop accessing a drive >>>>>> it autosuspends, and when I access it again it gets resumed and >>>>>> works -- as you would expect. >>>>> >>>>> that's weird. when I mount, everything looks good, "sda1". But as >>>>> soon as I cd to the mountpoint and do "ls" (on another SD card >>>>> "ls" works but actual file reading leads to the exact same >>>>> errors), I get: >>>>> >>>>> [ 77.474632] sd 0:0:0:0: [sda] tag#0 UNKNOWN(0x2003) Result: >>>>> hostbyte=0x00 driverbyte=0x08 cmd_age=0s >>>>> [ 77.474647] sd 0:0:0:0: [sda] tag#0 Sense Key : 0x6 [current] >>>>> [ 77.474655] sd 0:0:0:0: [sda] tag#0 ASC=0x28 ASCQ=0x0 >>>>> [ 77.474667] sd 0:0:0:0: [sda] tag#0 CDB: opcode=0x28 28 00 00 >>>>> 00 60 40 00 00 01 00 >>>> >>>> This error report comes from the SCSI layer, not the block layer. >>> >>> That sense code means "NOT READY TO READY CHANGE, MEDIUM MAY HAVE >>> CHANGED" so it sounds like it something we should be >>> ignoring. Usually this signals a problem, like you changed the >>> medium manually (ejected the CD). But in this case you can tell us >>> to expect this by setting >>> >>> sdev->expecting_cc_ua >>> >>> And we'll retry. I think you need to set this on all resumed >>> devices. >> >> Actually, it's not quite that easy, we filter out this ASC/ASCQ >> combination from the check because we should never ignore medium might >> have changed events on running devices. We could ignore it if we had a >> flag to say the power has been yanked (perhaps an additional sdev flag >> you set on resume) but we would still miss the case where you really >> had powered off the drive and then changed the media ... if you can >> regard this as the user's problem, then we might have a solution. > > Indeed, I was going to make the same point. > > The only reasonable conclusion is that suspending these SD card readers > isn't safe unless they don't contain a card -- or maybe just if the > device file isn't open or mounted. > > Although support for this sort of thing could be added to the kernel, > for now it's best to rely on userspace doing the right thing. The > kernel doesn't even know which devices suffer from this problem. > > well, userspace can do something like "automatically unmount if not used" but that is *way* more inefficient than if the kernel would support this is some way or another, for SD cards.
