re: D_MPSAFE drivers

[matthew green <mrg%eterna.com.au@localhost>]

coypu%SDF.ORG@localhost writes:
> Hi!
> 
> Poking around I noticed KERNEL_LOCK is occasionally
> grabbed by cdev_* for noticeable periods of time.
> 
> Looking at the code, it grabs DEV_LOCK which is effectively
> KERNEL_LOCK if the driver is not declared MPSAFE.
> 
> It appears that many "big name" drivers (wd, nvme) do
> not have d_flags D_MPSAFE, unless I am reading things
> wrong.

yes.  when something with the kernel lock taken sleeps,
the lock is dropped.  rarely do these drivers run for a
long time without sleeping.  so while definitely something
we are planning to fix it, shouldn't be a place that the
kernel lock is helf for a long time.


.mrg.