On Tue, Jan 28 2020 at 9:32am -0500, Stefan Bader <stefan.bader@xxxxxxxxxxxxx> wrote: > On 27.01.20 20:32, Mike Snitzer wrote: > > > > I just staged the following DM fix: > > https://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm.git/commit/?h=dm-5.6&id=28a101d6b344f5a38d482a686d18b1205bc92333 > > Thanks Mike, > > yeah this looks like it resolves the problem without adding any impact on the > generic I/O path. We certainly had thought about that but felt uncertain whether > it would not open other risks. Like something adding requests just before the > table load. Could this cause some I/O be handled by one function and the rest by > another? And would that really matter? I considered this too. Any IO issued to the device before it is "ready" won't matter anyway (no where to send the IO due to not having a DM table -- such IO should result in an error (from dm.c:dm_process_bio's !map check). But given the device has no size, a simple write will hit -ENOSPC before. And the only way to get the DM device to have a proper destination for its IO is to load a table, which requires a sequence like: # dmsetup create -n test # dmsetup table test: # echo "0 20971520 linear 259:0 2048" | dmsetup load test # dmsetup table --inactive test: 0 20971520 linear 259:0 2048 # dmsetup suspend test # dmsetup resume test # dmsetup table test: 0 20971520 linear 259:0 2048 And once a table is loaded there will be accompanying change uevents that trigger udev, blkid, etc. (NOTE: the suspend phase implies a flush of all outstanding IO, but even if 'dmsetup suspend --noflush test' were used the IO would just get pushed onto a list in DM core and it would be issued after the new table is in place). > The other thing that was a bit strange but maybe someone else's problem is that > mount generated I/O requests to start with. The device size should be 0 still. That's just mount not having a negative check for device size being 0. Mike
