kernel: Add thread setting to prevent page waits and use it in the file cache.

See inline comment: otherwise we could deadlock waiting for busy pages.

At the same time, make page_faults_allowed just an int16 and drop
atomics and extra checks, they aren't needed.

Fixes #19441.

Change-Id: I1b7cc06f66b44c3520fa36497c076ee5a6320706
Reviewed-on: https://review.haiku-os.org/c/haiku/+/9120
Tested-by: Commit checker robot <[email protected]>
Reviewed-by: waddlesplash <[email protected]>

headers/private/kernel/thread_types.h

@@ -287,8 +287,8 @@ struct Thread : TeamThreadIteratorEntry<thread_id>, KernelReferenceable {
 
 	void			(*fault_handler)(void);
 	jmp_buf			fault_handler_state;
-	int32			page_faults_allowed;
-		/* this field may only stay in debug builds in the future */
+	int16			page_faults_allowed;
+	int16			page_fault_waits_allowed;
 
 	BKernel::Team	*team;	// protected by team lock, thread lock, scheduler
 							// lock, team_lock

headers/private/kernel/vm/vm.h

@@ -68,8 +68,8 @@ void slab_init_post_sem();
 void slab_init_post_thread();
 
 // to protect code regions with interrupts turned on
-void permit_page_faults(void);
-void forbid_page_faults(void);
+void permit_page_faults();
+void forbid_page_faults();
 
 // private kernel only extension (should be moved somewhere else):
 area_id create_area_etc(team_id team, const char *name, size_t size,