On 13.09.2018 18:30, Chris Murphy wrote:
> This is the 2nd or 3rd thread containing hanging btrfs send, with
> kernel 4.18.x. The subject of one is "btrfs send hung in pipe_wait"
> and the other I can't find at the moment. In that case though the hang
> is reproducible in 4.14.x and weirdly it only happens when a snapshot
> contains (perhaps many) reflinks. Scrub and check lowmem find nothing
> wrong.
>
> I have snapshots with a few reflinks (cp --reflink and also
> deduplication), and I see maybe 15-30 second hangs where nothing is
> apparently happening (in top or iotop), but I'm also not seeing any
> blocked tasks or high CPU usage. Perhaps in my case it's just
> recovering quickly.
>
> Are there any kernel config options in "# Debug Lockups and Hangs"
> that might hint at what's going on? Some of these are enabled in
> Fedora debug kernels, which are built practically daily, e.g. right
> now the latest in the build system is 4.19.0-0.rc3.git2.1 - which
> translates to git 54eda9df17f3.
If it's a lock-related problem then you need Lock Debugging => Lock
debugging: prove locking correctness
>
>
> Chris Murphy
>
