This is indeed a regression.
Perhaps we should also revert:
12a0b6622107 ("nvme: don't hold nvmf_transports_rwsem for more
than transport lookups")
Which inherently caused this by removing the serialization of
.create_ctrl()...
no, I believe the patch on the semaphore is correct. Otherwise -
things can be blocked a long time.. a minute (1 cmd timeout) or
even multiple minutes in the case where a command failure in core
layers effectively gets ignored and thus doesn't cause the error
path in the transport. There can be multiple /dev/nvme-fabrics
commands stacked up that can make the delays look much longer to
the last guy.
as far as creation vs teardown... yeah, not fun, but there are
other ways to deal with it. FC: I got rid of the separate
create/reconnect threads a while ago thus the
return-control-while-reconnecting behavior, so I've had to deal
with it. It's one area it'd be nice to see some convergence in
implementation again between transports.
Doesn't fc have a bug there? in create_ctrl after flushing the
connect_work, what is telling it if delete is running in with it
(or that it already ran...)
I guess I don't understand what the bug is you are thinking about.
Maybe there's a short period that the ctrl ptr is perhaps freed, thus
the pointer shouldn't be used - but I don't see it as almost
everything is simply looking at the value of the pointer, not
dereferencing it.
I'm referring to nvme_fc_init_ctrl, if delete happens while it
is waiting in flush_delayed_work(&ctrl->connect_work); won't you
dereference and return a controller that is possibly already
deleted/freed?
ok - that matches my "short period" and it is possible as there's one
immediate printf that may dereference the ptr. After that, it's
comparisons of the pointer value. I can move the printf to avoid the
issue. That window's rather small.
But you also return back &ctrl->ctrl, that is another dereference, and
what will make ctrl to be an ERR_PTR?
Anyway, we should probably come up with something more robust...
I do have a bug or two with delete association fighting with
create_association - but it's mainly due to nvme_fc_error_recovery
not the delete routine. I've reworked this area after seeing your
other patches and will be posting after some more testing. But no
reason for synchronizing all ctrl creates.
Is it that big of an issue? it should fail rather quickly shouldn't it?
not sure what you are asking. if it's how long to fail the creation of
a new association - it's at least 60s (an admin command timeout).
That's the worst case (admin command timeout), but is it the most common
case?
Would making the timeouts shorter in the initial connect make sense?
Just throwing out ideas...
