CVS commit: src/sys/arch/arm/arm32

["Manuel Bouyer" <bouyer%netbsd.org@localhost>]

Module Name:    src
Committed By:   bouyer
Date:           Tue Apr 23 11:21:21 UTC 2019

Modified Files:
        src/sys/arch/arm/arm32: pmap.c

Log Message:
Fix a deadlock between the pool and pmap codes:
- cpu0 grabs the kernel lock (e.g. from a non-MPSAFE interrupt) and
  calls pool_get().
- cpu1 does a pool_get() on the same pool from MPSAFE code, which needs a
  pool_page_alloc(), which ends up in pmap_extract_coherency().

So cpu0 holds the kernel_lock and wants the pool lock. cpu1 holds the pool
lock and wants the kernel_lock in pmap_extract_coherency().

The pmap code should not rely on kernel_lock. Intead make the
pmap_kernel()->pm_obj_lock a IPL_VM lock and use it as pmap lock
(thus dropping the pmap test pmap_{acquire,release}_pmap_lock()).
This needs to be a IPL_VM because unlike user pmaps, this can be locked
from interrupt context.

Add a IPL_NONE lock for pmap_growkernel(). We can't use
pmap_kernel()->pm_obj_lock here because pmap_grow_map() may sleep.

Make pmap_lock (which may be locked with pm_obj_lock held) a IPL_VM
lock in all case.

reorder a few things to not call pool_get()/pool_put() (which may sleep)
with pm_obj_lock held.

Patch initially posted to port-arm@ on April 19, improved patch (per
suggestions from Nick Hudson and Jason Thorpe) on April 21.


To generate a diff of this commit:
cvs rdiff -u -r1.372 -r1.373 src/sys/arch/arm/arm32/pmap.c

Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.