Kernel: Lock the inode before writing in SharedInodeVMObject::sync

We ensure that when we call SharedInodeVMObject::sync we lock the inode
lock before calling Inode virtual write_bytes method directly to avoid
assertion on the unlocked inode lock, as it was regressed recently. This
is not a complete fix as the need to lock from each path before calling
the write_bytes method should be avoided because it can lead to
hard-to-find bugs, and this commit only fixes the problem temporarily.

Kernel/FileSystem/Inode.h

@@ -19,6 +19,7 @@
 #include <Kernel/Forward.h>
 #include <Kernel/Library/ListedRefCounted.h>
 #include <Kernel/Locking/Mutex.h>
+#include <Kernel/Memory/SharedInodeVMObject.h>
 
 namespace Kernel {
 
@@ -32,6 +33,7 @@ class Inode : public ListedRefCounted<Inode, LockType::Spinlock>
     friend class VirtualFileSystem;
     friend class FileSystem;
     friend class InodeFile;
+    friend class Kernel::Memory::SharedInodeVMObject; // FIXME: Remove when write_bytes becomes non-virtual
 
 public:
     virtual ~Inode();

Kernel/Memory/SharedInodeVMObject.cpp

@@ -53,6 +53,7 @@ ErrorOr<void> SharedInodeVMObject::sync(off_t offset_in_pages, size_t pages)
         u8 page_buffer[PAGE_SIZE];
         MM.copy_physical_page(*physical_page, page_buffer);
 
+        MutexLocker locker(m_inode->m_inode_lock);
         TRY(m_inode->write_bytes(page_index * PAGE_SIZE, PAGE_SIZE, UserOrKernelBuffer::for_kernel_buffer(page_buffer), nullptr));
     }