[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [DRBD-user] [PATCH] xen-blkback: Switch to closed state after releasing the backing device
On Mon, Sep 10, 2018 at 03:22:52PM +0200, Valentin Vidic wrote: > On Mon, Sep 10, 2018 at 02:45:31PM +0200, Lars Ellenberg wrote: > > On Sat, Sep 08, 2018 at 09:34:32AM +0200, Valentin Vidic wrote: > > > On Fri, Sep 07, 2018 at 07:14:59PM +0200, Valentin Vidic wrote: > > > > In fact the first one is the original code path before I modified > > > > blkback. The problem is it gets executed async from workqueue so > > > > it might not always run before the call to drbdadm secondary. > > > > > > As the DRBD device gets released only when the last IO request > > > has finished, I found a way to check and wait for this in the > > > block-drbd script: > > > > > --- block-drbd.orig 2018-09-08 09:07:23.499648515 +0200 > > > +++ block-drbd 2018-09-08 09:28:12.892193649 +0200 > > > @@ -230,6 +230,24 @@ > > > and so cannot be mounted ${m2}${when}." > > > } > > > > > > +wait_for_inflight() > > > +{ > > > + local dev="$1" > > > + local inflight="/sys/block/${dev#/dev/}/inflight" > > > + local rd wr > > > + > > > + if ! [ -f "$inflight" ]; then > > > + return > > > + fi > > > + > > > + while true; do > > > + read rd wr < $inflight > > > + if [ "$rd" = "0" -a "$wr" = "0" ]; then > > > > If it is "idle" now, but still "open", > > this will not sleep, and still fail the demotion below. > > True, but in this case blkback is holding it open until all > the writes have finished and the last write closes the device. > Since fuser can't check blkback this is an approximation that > seems to work because I don't get any failed drbdadm calls now. > > > You try to help it by "waiting forever until it appears to be idle". > > I suggest to at least limit the retries by iteration or time. > > And also (or, instead; but you'd potentially get a number of > > "scary messages" in the logs) add something like: > > Ok, should I open a PR to discuss this change further? > > > Or, well, yes, fix blkback to not "defer" the final close "too long", > > if at all possible. > > blkback needs to finish the writes on shutdown or I get a fsck errors > on next boot. Ideally XenbusStateClosed should be delayed until the > device release but currently it does not seem possible without breaking > other things. I can try to take a look at this and attempt to make sure the state is only changed to closed in blkback _after_ the device has been released, but it might take me a couple of days to get you a patch. I'm afraid that other hotplug scripts will also have issues with such behavior, and we shouldn't force all users of hotplug scripts to add such workarounds. Roger. _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxxx https://lists.xenproject.org/mailman/listinfo/xen-devel
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