> Date: Tue, 18 May 2021 12:02:19 +0200
> From: Martin Pieuchot <[email protected]>
>
> This allows us to not rely on the KERNEL_LOCK() to check reference
> counts.
>
> Also reduces differences with NetBSD and shrink my upcoming `vmobjlock'
> diff.
>
> ok?
Shouldn't we make ref_count volatile in that case?
> Index: uvm/uvm_map.c
> ===================================================================
> RCS file: /cvs/src/sys/uvm/uvm_map.c,v
> retrieving revision 1.274
> diff -u -p -r1.274 uvm_map.c
> --- uvm/uvm_map.c 26 Mar 2021 13:40:05 -0000 1.274
> +++ uvm/uvm_map.c 18 May 2021 09:36:55 -0000
> @@ -491,12 +491,13 @@ uvm_mapent_addr_remove(struct vm_map *ma
> /*
> * uvm_map_reference: add reference to a map
> *
> - * XXX check map reference counter lock
> + * => map need not be locked
> */
> -#define uvm_map_reference(_map)
> \
> - do { \
> - map->ref_count++; \
> - } while (0)
> +void
> +uvm_map_reference(struct vm_map *map)
> +{
> + atomic_inc_int(&map->ref_count);
> +}
>
> /*
> * Calculate the dused delta.
> @@ -4292,7 +4293,7 @@ uvm_map_deallocate(vm_map_t map)
> int c;
> struct uvm_map_deadq dead;
>
> - c = --map->ref_count;
> + c = atomic_dec_int_nv(&map->ref_count);
> if (c > 0) {
> return;
> }
> Index: uvm/uvm_map.h
> ===================================================================
> RCS file: /cvs/src/sys/uvm/uvm_map.h,v
> retrieving revision 1.69
> diff -u -p -r1.69 uvm_map.h
> --- uvm/uvm_map.h 12 Mar 2021 14:15:49 -0000 1.69
> +++ uvm/uvm_map.h 18 May 2021 09:36:36 -0000
> @@ -259,6 +259,7 @@ RBT_PROTOTYPE(uvm_map_addr, vm_map_entry
> * read_locks and write_locks are used in lock debugging code.
> *
> * Locks used to protect struct members in this file:
> + * a atomic operations
> * I immutable after creation or exec(2)
> * v `vm_map_lock' (this map `lock' or `mtx')
> */
> @@ -272,7 +273,7 @@ struct vm_map {
> struct uvm_map_addr addr; /* [v] Entry tree, by addr */
>
> vsize_t size; /* virtual size */
> - int ref_count; /* Reference count */
> + int ref_count; /* [a] Reference count */
> int flags; /* flags */
> struct mutex flags_lock; /* flags lock */
> unsigned int timestamp; /* Version number */
>
>
