On Wed, 5 Nov 2014, Mike Snitzer wrote: > On Wed, Nov 05 2014 at 9:37am -0500, > Mikulas Patocka <mpatocka@xxxxxxxxxx> wrote: > > > The patch series introduces two suspend mechanisms and it is unclear how > > should they interact with each other. > > And this point is not correct. As you know dm_internal_suspend and > dm_internal_resume interface predates any of my changes. > > That existing interface was extended them to be (mostly) fully formed > equivalents of dm_suspend() and dm_resume(). > > I say "mostly" because dm_internal_resume() doesn't call into the targets' > resume hooks because no existing callers (dm-stats or dm-thinp) need > to. But obviously dm_resume() does need to so it passes @resume_targets > as true to __dm_resume(). > > I'm not trying to suggest there is a bug or bugs in this new code (you > already pointed out the locking issue across ioctls that I fixed). > > But a bug doesn't implicitly mean this is an imperfect way forward -- > if/when a bug is found we'll deal with it.. so feel free to pour over > this code to see if there is a bug or bugs. I really do welcome your > review -- I would just like technical issues to be the focus of any > technical review. Problems with that patch set: 1. You walk all thin targets in pool_presuspend and call internal_suspend on them and then again in pool_resume call internal_resume on them. Between calls to pool_presuspend and pool_resume, dm-thin devices may be added or removed, resulting in unballanced calls. 2. You walk all thin targets and call internal_suspend on them. If two thin targets are in one dm table, it calls internal_suspend twice on the same md device. It also calls internal_suspend twice on the same md device if the device has both active and inactive table with a thin target. 3. The device may be suspended internally by pool presuspend and by statistics at the same time - the code doesn't handle that: if (WARN_ON(dm_suspended_internally_md(md))) goto out; /* disallow nested internal suspends! */ 4. when pool_presuspend is called, md->suspend_lock is alrady held. Taking md->suspend_lock on another device results in lockdep warning. For reasons 1 and 2, I wouldn't really deal with "thin" targets at all - they may be created or deleted independent on pool status. Instead, we should block all active bios inside the pool - the bios are already registered in dm_deferred_set or in the prison, so all you need to do is to set a flag pool's presuspend method that causes all new bios to be queues and the wait until the prison is empty and the counters in deferred_set reach zero. Mikulas -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
