Re: [PATCH] softirq: fix memory corruption when freeing tasklet_struct

[Tejun Heo]

Hello,

The following is a draft patch which implements atomic workqueues and
convert dm-crypt to use it instead of tasklet. It's an early draft and very
lightly tested but seems to work more or less. It's on top of wq/for6.9 + a
pending patchset. The following git branch can be used for testing.

  git://git.kernel.org/pub/scm/linux/kernel/git/tj/wq.git wq-atomic-draft

I'll go over it to make sure all the pieces work. While it adds some
complications, it doesn't seem too bad and conversion from tasklet should be
straightforward too.

- It hooks into tasklet[_hi] for now but if we get to update all of tasklet
  users, we can just repurpose the tasklet softirq slots directly.

- I thought about allowing busy-waits for flushes and cancels but it didn't
  seem necessary. Keeping them blocking has the benefit of avoiding possible
  nasty deadlocks. We can revisit if there's need.

- Compared to tasklet, each work item goes through a bit more management
  code because I wanted to keep the code as unified as possible to regular
  threaded workqueues. That said, it's not a huge amount and my bet is that
  the difference is unlikely to be noticeable.

Thanks.