Comment 42 for bug 1796292

From a kernel perspective this big slowness on shutting down a bcache volume might be caused by a locking / race condition issue. If I read correctly this problem has been reproduced in bionic (and in xenial we even got a kernel oops - it looks like caused by a NULL pointer dereference). I would try to address these issues separately.

About bionic it would be nice to test this commit (also mentioned by @elmo in comment #28):

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=eb8cbb6df38f6e5124a3d5f1f8a3dbf519537c60

Moreover, even if we didn't get an explicit NULL pointer dereference with bionic, I think it would be interesting to test also the following fixes:

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=a4b732a248d12cbdb46999daf0bf288c011335eb
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=1f0ffa67349c56ea54c03ccfd1e073c990e7411e
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=9951379b0ca88c95876ad9778b9099e19a95d566

I've already backported all of them and applied to the latest bionic kernel. A test kernel is available here:

https://kernel.ubuntu.com/~arighi/LP-1796292/

If it doesn't cost too much it would be great to do a test with it. In the meantime I'll try to reproduce the problem locally. Thanks in advance!