Kernel: Don't hog the MM lock while unmapping regions

We were holding the MM lock across all of the region unmapping code.
This was previously necessary since the quickmaps used during unmapping
required holding the MM lock.

Now that it's no longer necessary, we can leave the MM lock alone here.

Kernel/Memory/AddressSpace.cpp

@@ -341,10 +341,9 @@ void AddressSpace::remove_all_regions(Badge<Process>)
     VERIFY(Thread::current() == g_finalizer);
     {
         SpinlockLocker pd_locker(m_page_directory->get_lock());
-        SpinlockLocker mm_locker(s_mm_lock);
         m_region_tree.with([&](auto& region_tree) {
             for (auto& region : region_tree.regions())
-                region.unmap_with_locks_held(ShouldFlushTLB::No, pd_locker, mm_locker);
+                region.unmap_with_locks_held(ShouldFlushTLB::No, pd_locker);
         });
     }
 

Kernel/Memory/Region.cpp

@@ -70,8 +70,7 @@ Region::~Region()
         if (!is_readable() && !is_writable() && !is_executable()) {
             // If the region is "PROT_NONE", we didn't map it in the first place.
         } else {
-            SpinlockLocker mm_locker(s_mm_lock);
-            unmap_with_locks_held(ShouldFlushTLB::Yes, pd_locker, mm_locker);
+            unmap_with_locks_held(ShouldFlushTLB::Yes, pd_locker);
             VERIFY(!m_page_directory);
         }
     }
@@ -268,11 +267,10 @@ void Region::unmap(ShouldFlushTLB should_flush_tlb)
     if (!m_page_directory)
         return;
     SpinlockLocker pd_locker(m_page_directory->get_lock());
-    SpinlockLocker mm_locker(s_mm_lock);
-    unmap_with_locks_held(should_flush_tlb, pd_locker, mm_locker);
+    unmap_with_locks_held(should_flush_tlb, pd_locker);
 }
 
-void Region::unmap_with_locks_held(ShouldFlushTLB should_flush_tlb, SpinlockLocker<RecursiveSpinlock>&, SpinlockLocker<RecursiveSpinlock>&)
+void Region::unmap_with_locks_held(ShouldFlushTLB should_flush_tlb, SpinlockLocker<RecursiveSpinlock>&)
 {
     if (!m_page_directory)
         return;

Kernel/Memory/Region.h

@@ -183,7 +183,7 @@ public:
     void set_page_directory(PageDirectory&);
     ErrorOr<void> map(PageDirectory&, ShouldFlushTLB = ShouldFlushTLB::Yes);
     void unmap(ShouldFlushTLB = ShouldFlushTLB::Yes);
-    void unmap_with_locks_held(ShouldFlushTLB, SpinlockLocker<RecursiveSpinlock>& pd_locker, SpinlockLocker<RecursiveSpinlock>& mm_locker);
+    void unmap_with_locks_held(ShouldFlushTLB, SpinlockLocker<RecursiveSpinlock>& pd_locker);
 
     void remap();