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. -- Jens Axboe -- 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
