Hello Neil, Jes,
I wonder if the following deadlock is possible:
- Caller calls blk_start_plug and wants to submit two WRITE bios
- First bio successfully calls wait_barrier() and is appended to
plug->pending list
- Now somebody does freeze_array()
- freeze_array() unconditionally sets:
conf->array_frozen = 1;
and starts waiting for conf->nr_pending to go down
- Second WRITE bio calls wait_barrier, but it will wait for
"!conf->array_frozen" until it can proceed
- Now we have a deadlock: first bio will not be submitted because it
sits on the plug list of the caller, and caller is stuck in
wait_barrier, so it cannot do blk_finish_plug.
I am about to try to reproduce it on kernel 3.18, but looking at the
latest Linus tree, I don't see something preventing this from
happening either. Am I missing something?
Thanks,
Alex.