From 210689281f1eee5c635dc20aed110410e1d36424 Mon Sep 17 00:00:00 2001
From: Andreas Kling <kling@serenityos.org>
Date: Thu, 3 Feb 2022 01:37:46 +0100
Subject: [PATCH] Kernel: Protect mounted filesystem list with spinlock instead
 of mutex

---
 Kernel/FileSystem/VirtualFileSystem.cpp | 14 +++++++-------
 Kernel/FileSystem/VirtualFileSystem.h   |  4 ++--
 2 files changed, 9 insertions(+), 9 deletions(-)

diff --git a/Kernel/FileSystem/VirtualFileSystem.cpp b/Kernel/FileSystem/VirtualFileSystem.cpp
index 8a4f68737b..8efdacc338 100644
--- a/Kernel/FileSystem/VirtualFileSystem.cpp
+++ b/Kernel/FileSystem/VirtualFileSystem.cpp
@@ -52,7 +52,7 @@ InodeIdentifier VirtualFileSystem::root_inode_id() const
 
 ErrorOr<void> VirtualFileSystem::mount(FileSystem& fs, Custody& mount_point, int flags)
 {
-    return m_mounts.with_exclusive([&](auto& mounts) -> ErrorOr<void> {
+    return m_mounts.with([&](auto& mounts) -> ErrorOr<void> {
         auto& inode = mount_point.inode();
         dbgln("VirtualFileSystem: Mounting {} at inode {} with flags {}",
             fs.class_name(),
@@ -67,7 +67,7 @@ ErrorOr<void> VirtualFileSystem::mount(FileSystem& fs, Custody& mount_point, int
 
 ErrorOr<void> VirtualFileSystem::bind_mount(Custody& source, Custody& mount_point, int flags)
 {
-    return m_mounts.with_exclusive([&](auto& mounts) -> ErrorOr<void> {
+    return m_mounts.with([&](auto& mounts) -> ErrorOr<void> {
         dbgln("VirtualFileSystem: Bind-mounting inode {} at inode {}", source.inode().identifier(), mount_point.inode().identifier());
         // FIXME: check that this is not already a mount point
         Mount mount { source.inode(), mount_point, flags };
@@ -92,7 +92,7 @@ ErrorOr<void> VirtualFileSystem::unmount(Inode& guest_inode)
 {
     dbgln("VirtualFileSystem: unmount called with inode {}", guest_inode.identifier());
 
-    return m_mounts.with_exclusive([&](auto& mounts) -> ErrorOr<void> {
+    return m_mounts.with([&](auto& mounts) -> ErrorOr<void> {
         for (size_t i = 0; i < mounts.size(); ++i) {
             auto& mount = mounts[i];
             if (&mount.guest() != &guest_inode)
@@ -126,7 +126,7 @@ ErrorOr<void> VirtualFileSystem::mount_root(FileSystem& fs)
     auto pseudo_path = TRY(static_cast<FileBackedFileSystem&>(fs).file_description().pseudo_path());
     dmesgln("VirtualFileSystem: mounted root from {} ({})", fs.class_name(), pseudo_path);
 
-    m_mounts.with_exclusive([&](auto& mounts) {
+    m_mounts.with([&](auto& mounts) {
         mounts.append(move(mount));
     });
 
@@ -136,7 +136,7 @@ ErrorOr<void> VirtualFileSystem::mount_root(FileSystem& fs)
 
 auto VirtualFileSystem::find_mount_for_host(InodeIdentifier id) -> Mount*
 {
-    return m_mounts.with_exclusive([&](auto& mounts) -> Mount* {
+    return m_mounts.with([&](auto& mounts) -> Mount* {
         for (auto& mount : mounts) {
             if (mount.host() && mount.host()->identifier() == id)
                 return &mount;
@@ -147,7 +147,7 @@ auto VirtualFileSystem::find_mount_for_host(InodeIdentifier id) -> Mount*
 
 auto VirtualFileSystem::find_mount_for_guest(InodeIdentifier id) -> Mount*
 {
-    return m_mounts.with_exclusive([&](auto& mounts) -> Mount* {
+    return m_mounts.with([&](auto& mounts) -> Mount* {
         for (auto& mount : mounts) {
             if (mount.guest().identifier() == id)
                 return &mount;
@@ -724,7 +724,7 @@ ErrorOr<void> VirtualFileSystem::rmdir(StringView path, Custody& base)
 
 void VirtualFileSystem::for_each_mount(Function<IterationDecision(Mount const&)> callback) const
 {
-    m_mounts.with_shared([&](auto& mounts) {
+    m_mounts.with([&](auto& mounts) {
         for (auto& mount : mounts) {
             if (callback(mount) == IterationDecision::Break)
                 break;
diff --git a/Kernel/FileSystem/VirtualFileSystem.h b/Kernel/FileSystem/VirtualFileSystem.h
index 9fbde822ca..72993c3093 100644
--- a/Kernel/FileSystem/VirtualFileSystem.h
+++ b/Kernel/FileSystem/VirtualFileSystem.h
@@ -19,7 +19,7 @@
 #include <Kernel/FileSystem/Mount.h>
 #include <Kernel/FileSystem/UnveilNode.h>
 #include <Kernel/Forward.h>
-#include <Kernel/Locking/MutexProtected.h>
+#include <Kernel/Locking/SpinlockProtected.h>
 
 namespace Kernel {
 
@@ -95,7 +95,7 @@ private:
     RefPtr<Inode> m_root_inode;
     RefPtr<Custody> m_root_custody;
 
-    MutexProtected<Vector<Mount, 16>> m_mounts;
+    SpinlockProtected<Vector<Mount, 16>> m_mounts;
 };
 
 }