Jens Axboe <axboe@xxxxxxxxx> writes: > On 2012-09-28 17:02, Jeff Moyer wrote: >> Jens Axboe <axboe@xxxxxxxxx> writes: >> >>> On 2012-09-28 08:09, Dave Chinner wrote: >>>> From: Dave Chinner <dchinner@xxxxxxxxxx> >>>> >>>> xfstests has always had random failures of tests due to loop devices >>>> failing to be torn down and hence leaving filesytems that cannot be >>>> unmounted. This causes test runs to immediately stop. >>>> >>>> Over the past 6 or 7 years we've added hacks like explicit unmount >>>> -d commands for loop mounts, losetup -d after unmount -d fails, etc, >>>> but still the problems persist. Recently, the frequency of loop >>>> related failures increased again to the point that xfstests 259 will >>>> reliably fail with a stray loop device that was not torn down. >>>> >>>> That is despite the fact the test is above as simple as it gets - >>>> loop 5 or 6 times running mkfs.xfs with different paramters: >>>> >>>> lofile=$(losetup -f) >>>> losetup $lofile "$testfile" >>>> "$MKFS_XFS_PROG" -b size=512 $lofile >/dev/null || echo "mkfs failed!" >>>> sync >>>> losetup -d $lofile >>>> >>>> And losteup -d $lofile is failing with EBUSY on 1-3 of these loops >>>> every time the test is run. >>>> >>>> Turns out that blkid is running simultaneously with losetup -d, and >>>> so it sees an elevated reference count and returns EBUSY. But why >>>> is blkid running? It's obvious, isn't it? udev has decided to try >>>> and find out what is on the block device as a result of a creation >>>> notification. And it is racing with mkfs, so might still be scanning >>>> the device when mkfs finishes and we try to tear it down. >>>> >>>> So, make losetup -d force autoremove behaviour. That is, when the >>>> last reference goes away, tear down the device. xfstests wants it >>>> *gone*, not causing random teardown failures when we know that all >>>> the operations the tests have specifically run on the device have >>>> completed and are no longer referencing the loop device. >>> >>> I hear that %^#@#! blkid behavior, it is such a pain in the neck. I >>> don't know how many times I've had to explain that behaviour to people >>> who run write testing with tracing, wonder wtf there are reads in the >>> trace. >>> >>> Patch looks fine, seems like the sane thing to do (lazy-remove on last >>> drop) for this case. >> >> Do we also want to prevent further opens? > > That's not a bad idea, at least it would be the logical thing to do. But > it does get into the realm of potentially breaking existing behaviour. What do you think could rely on the existing behaviour (that isn't broken by design)? -Jeff -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
