Kernel: Move ProcFS related overrides in Process to ProcessProcFSTraits

This allows us to 1) let go of the Process when an inode is ref'ing for
ProcFSExposedComponent related reasons, and 2) change our ref/unref
implementation.

Kernel/CMakeLists.txt

@@ -182,6 +182,7 @@ set(KERNEL_SOURCES
     ProcessExposed.cpp
     ProcessSpecificExposed.cpp
     ProcessGroup.cpp
+    ProcessProcFSTraits.cpp
     RTC.cpp
     Random.cpp
     Scheduler.cpp

Kernel/FileSystem/ProcFS.cpp

@@ -274,13 +274,15 @@ InodeMetadata ProcFSProcessDirectoryInode::metadata() const
     auto process = Process::from_pid(associated_pid());
     if (!process)
         return {};
+
+    auto traits = process->procfs_traits();
     InodeMetadata metadata;
-    metadata.inode = { fsid(), process->component_index() };
+    metadata.inode = { fsid(), traits->component_index() };
-    metadata.mode = S_IFDIR | process->required_mode();
+    metadata.mode = S_IFDIR | traits->required_mode();
-    metadata.uid = process->owner_user();
+    metadata.uid = traits->owner_user();
-    metadata.gid = process->owner_group();
+    metadata.gid = traits->owner_group();
     metadata.size = 0;
-    metadata.mtime = process->modified_time();
+    metadata.mtime = traits->modified_time();
     return metadata;
 }
 
@@ -295,7 +297,7 @@ KResult ProcFSProcessDirectoryInode::traverse_as_directory(Function<bool(FileSys
     auto process = Process::from_pid(associated_pid());
     if (!process)
         return EINVAL;
-    return process->traverse_as_directory(procfs().fsid(), move(callback));
+    return process->procfs_traits()->traverse_as_directory(procfs().fsid(), move(callback));
 }
 
 KResultOr<NonnullRefPtr<Inode>> ProcFSProcessDirectoryInode::lookup(StringView name)
@@ -400,13 +402,15 @@ InodeMetadata ProcFSProcessSubDirectoryInode::metadata() const
     auto process = Process::from_pid(associated_pid());
     if (!process)
         return {};
+
+    auto traits = process->procfs_traits();
     InodeMetadata metadata;
-    metadata.inode = { fsid(), process->component_index() };
+    metadata.inode = { fsid(), traits->component_index() };
-    metadata.mode = S_IFDIR | process->required_mode();
+    metadata.mode = S_IFDIR | traits->required_mode();
-    metadata.uid = process->owner_user();
+    metadata.uid = traits->owner_user();
-    metadata.gid = process->owner_group();
+    metadata.gid = traits->owner_group();
     metadata.size = 0;
-    metadata.mtime = process->modified_time();
+    metadata.mtime = traits->modified_time();
     return metadata;
 }
 
@@ -522,13 +526,15 @@ InodeMetadata ProcFSProcessPropertyInode::metadata() const
     auto process = Process::from_pid(associated_pid());
     if (!process)
         return {};
+
+    auto traits = process->procfs_traits();
     InodeMetadata metadata;
-    metadata.inode = { fsid(), process->component_index() };
+    metadata.inode = { fsid(), traits->component_index() };
     metadata.mode = determine_procfs_process_inode_mode(m_parent_sub_directory_type, m_possible_data.property_type);
-    metadata.uid = process->owner_user();
+    metadata.uid = traits->owner_user();
-    metadata.gid = process->owner_group();
+    metadata.gid = traits->owner_group();
     metadata.size = 0;
-    metadata.mtime = process->modified_time();
+    metadata.mtime = traits->modified_time();
     return metadata;
 }
 KResult ProcFSProcessPropertyInode::traverse_as_directory(Function<bool(FileSystem::DirectoryEntryView const&)>) const

Kernel/GlobalProcessExposed.cpp

@@ -944,8 +944,9 @@ KResultOr<NonnullRefPtr<ProcFSExposedComponent>> ProcFSRootDirectory::lookup(Str
     auto actual_pid = pid.value();
 
     auto maybe_process = Process::from_pid(actual_pid);
-    if (maybe_process)
+    if (maybe_process) {
-        return maybe_process.release_nonnull();
+        return maybe_process->procfs_traits();
+    }
     return ENOENT;
 }
 

Kernel/Process.cpp

@@ -260,6 +260,11 @@ Process::Process(const String& name, uid_t uid, gid_t gid, ProcessID ppid, bool
     m_protected_values.suid = uid;
     m_protected_values.sgid = gid;
 
+    auto maybe_procfs_traits = ProcessProcFSTraits::try_create({}, make_weak_ptr());
+    // NOTE: This can fail, but it should be very, *very* rare.
+    VERIFY(!maybe_procfs_traits.is_error());
+    m_procfs_traits = maybe_procfs_traits.release_value();
+
     dbgln_if(PROCESS_DEBUG, "Created new process {}({})", m_name, this->pid().value());
 }
 

Kernel/Process.h

@@ -85,10 +85,9 @@ typedef HashMap<FlatPtr, RefPtr<FutexQueue>> FutexQueues;
 struct LoadResult;
 
 class Process
-    : public ProcFSExposedComponent
+    : public RefCounted<Process>
     , public Weakable<Process> {
 
-private:
     class ProtectedValues {
     public:
         ProcessID pid { 0 };
@@ -145,6 +144,8 @@ public:
     };
 
 public:
+    class ProcessProcFSTraits;
+
     inline static Process* current()
     {
         auto current_thread = Processor::current_thread();
@@ -549,13 +550,7 @@ private:
     void setup_socket_fd(int fd, NonnullRefPtr<FileDescription> description, int type);
 
 public:
-    // ^ProcFSExposedComponent stats
+    NonnullRefPtr<ProcessProcFSTraits> procfs_traits() const { return *m_procfs_traits; }
-    virtual InodeIndex component_index() const override;
-    virtual KResultOr<NonnullRefPtr<Inode>> to_inode(const ProcFS& procfs_instance) const override;
-    virtual KResult traverse_as_directory(unsigned, Function<bool(FileSystem::DirectoryEntryView const&)>) const override;
-    virtual mode_t required_mode() const override { return 0555; }
-    virtual uid_t owner_user() const override { return uid(); }
-    virtual gid_t owner_group() const override { return gid(); }
     KResult procfs_get_fds_stats(KBufferBuilder& builder) const;
     KResult procfs_get_perf_events(KBufferBuilder& builder) const;
     KResult procfs_get_unveil_stats(KBufferBuilder& builder) const;
@@ -713,6 +708,37 @@ public:
         FileDescriptionAndFlags* m_description { nullptr };
     };
 
+    class ProcessProcFSTraits : public ProcFSExposedComponent {
+    public:
+        static KResultOr<NonnullRefPtr<ProcessProcFSTraits>> try_create(Badge<Process>, WeakPtr<Process> process)
+        {
+            auto result = adopt_ref_if_nonnull(new (nothrow) ProcessProcFSTraits(process));
+            if (!result)
+                return ENOMEM;
+
+            return result.release_nonnull();
+        }
+
+        virtual InodeIndex component_index() const override;
+        virtual KResultOr<NonnullRefPtr<Inode>> to_inode(const ProcFS& procfs_instance) const override;
+        virtual KResult traverse_as_directory(unsigned, Function<bool(FileSystem::DirectoryEntryView const&)>) const override;
+        virtual mode_t required_mode() const override { return 0555; }
+
+        virtual uid_t owner_user() const override;
+
+        virtual gid_t owner_group() const override;
+
+    private:
+        ProcessProcFSTraits(WeakPtr<Process> process)
+            : m_process(process)
+        {
+        }
+
+        // NOTE: We need to weakly hold on to the process, because otherwise
+        //       we would be creating a reference cycle.
+        WeakPtr<Process> m_process;
+    };
+
     FileDescriptions& fds() { return m_fds; }
     const FileDescriptions& fds() const { return m_fds; }
 
@@ -770,9 +796,10 @@ private:
     };
 
     Array<CoredumpProperty, 4> m_coredump_properties;
-
     NonnullRefPtrVector<Thread> m_threads_for_coredump;
 
+    mutable RefPtr<ProcessProcFSTraits> m_procfs_traits;
+
     static_assert(sizeof(ProtectedValues) < (PAGE_SIZE));
     alignas(4096) ProtectedValues m_protected_values;
     u8 m_protected_values_padding[PAGE_SIZE - sizeof(ProtectedValues)];

Kernel/ProcessProcFSTraits.cpp

@@ -0,0 +1,72 @@
+/*
+ * Copyright (c) 2021, sin-ack <sin-ack@protonmail.com>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <Kernel/FileSystem/ProcFS.h>
+#include <Kernel/Process.h>
+
+namespace Kernel {
+
+uid_t Process::ProcessProcFSTraits::owner_user() const
+{
+    auto process = m_process.strong_ref();
+    if (!process)
+        return 0;
+
+    return process->uid();
+}
+
+gid_t Process::ProcessProcFSTraits::owner_group() const
+{
+    auto process = m_process.strong_ref();
+    if (!process)
+        return 0;
+
+    return process->gid();
+}
+
+InodeIndex Process::ProcessProcFSTraits::component_index() const
+{
+    auto process = m_process.strong_ref();
+    if (!process)
+        return {};
+
+    return SegmentedProcFSIndex::build_segmented_index_for_pid_directory(process->pid());
+}
+
+KResultOr<NonnullRefPtr<Inode>> Process::ProcessProcFSTraits::to_inode(const ProcFS& procfs_instance) const
+{
+    auto process = m_process.strong_ref();
+    if (!process)
+        return ESRCH;
+
+    auto maybe_inode = ProcFSProcessDirectoryInode::try_create(procfs_instance, process->pid());
+    if (maybe_inode.is_error())
+        return maybe_inode.error();
+    return maybe_inode.release_value();
+}
+
+KResult Process::ProcessProcFSTraits::traverse_as_directory(unsigned fsid, Function<bool(FileSystem::DirectoryEntryView const&)> callback) const
+{
+    auto process = m_process.strong_ref();
+    if (!process)
+        return ESRCH;
+
+    callback({ ".", { fsid, SegmentedProcFSIndex::build_segmented_index_for_pid_directory(process->pid()) }, 0 });
+    callback({ "..", { fsid, ProcFSComponentRegistry::the().root_directory().component_index() }, 0 });
+    callback({ "fd", { fsid, SegmentedProcFSIndex::build_segmented_index_for_sub_directory(process->pid(), SegmentedProcFSIndex::ProcessSubDirectory::FileDescriptions) }, 0 });
+    callback({ "stacks", { fsid, SegmentedProcFSIndex::build_segmented_index_for_sub_directory(process->pid(), SegmentedProcFSIndex::ProcessSubDirectory::Stacks) }, 0 });
+    callback({ "unveil", { fsid, SegmentedProcFSIndex::build_segmented_index_for_main_property_in_pid_directory(process->pid(), SegmentedProcFSIndex::MainProcessProperty::Unveil) }, 0 });
+    callback({ "pledge", { fsid, SegmentedProcFSIndex::build_segmented_index_for_main_property_in_pid_directory(process->pid(), SegmentedProcFSIndex::MainProcessProperty::Pledge) }, 0 });
+    callback({ "fds", { fsid, SegmentedProcFSIndex::build_segmented_index_for_main_property_in_pid_directory(process->pid(), SegmentedProcFSIndex::MainProcessProperty::FileDescriptions) }, 0 });
+    callback({ "exe", { fsid, SegmentedProcFSIndex::build_segmented_index_for_main_property_in_pid_directory(process->pid(), SegmentedProcFSIndex::MainProcessProperty::BinaryLink) }, 0 });
+    callback({ "cwd", { fsid, SegmentedProcFSIndex::build_segmented_index_for_main_property_in_pid_directory(process->pid(), SegmentedProcFSIndex::MainProcessProperty::CurrentWorkDirectoryLink) }, 0 });
+    callback({ "perf_events", { fsid, SegmentedProcFSIndex::build_segmented_index_for_main_property_in_pid_directory(process->pid(), SegmentedProcFSIndex::MainProcessProperty::PerformanceEvents) }, 0 });
+    callback({ "vm", { fsid, SegmentedProcFSIndex::build_segmented_index_for_main_property_in_pid_directory(process->pid(), SegmentedProcFSIndex::MainProcessProperty::VirtualMemoryStats) }, 0 });
+    callback({ "root", { fsid, SegmentedProcFSIndex::build_segmented_index_for_main_property_in_pid_directory(process->pid(), SegmentedProcFSIndex::MainProcessProperty::RootLink) }, 0 });
+    return KSuccess;
+}
+
+}

Kernel/ProcessSpecificExposed.cpp

@@ -40,40 +40,10 @@ KResultOr<size_t> Process::procfs_get_thread_stack(ThreadID thread_id, KBufferBu
     return KSuccess;
 }
 
-InodeIndex Process::component_index() const
-{
-    return SegmentedProcFSIndex::build_segmented_index_for_pid_directory(pid());
-}
-
-KResultOr<NonnullRefPtr<Inode>> Process::to_inode(const ProcFS& procfs_instance) const
-{
-    auto maybe_inode = ProcFSProcessDirectoryInode::try_create(procfs_instance, m_protected_values.pid);
-    if (maybe_inode.is_error())
-        return maybe_inode.error();
-    return maybe_inode.release_value();
-}
-
-KResult Process::traverse_as_directory(unsigned fsid, Function<bool(FileSystem::DirectoryEntryView const&)> callback) const
-{
-    callback({ ".", { fsid, SegmentedProcFSIndex::build_segmented_index_for_pid_directory(pid()) }, 0 });
-    callback({ "..", { fsid, ProcFSComponentRegistry::the().root_directory().component_index() }, 0 });
-    callback({ "fd", { fsid, SegmentedProcFSIndex::build_segmented_index_for_sub_directory(pid(), SegmentedProcFSIndex::ProcessSubDirectory::FileDescriptions) }, 0 });
-    callback({ "stacks", { fsid, SegmentedProcFSIndex::build_segmented_index_for_sub_directory(pid(), SegmentedProcFSIndex::ProcessSubDirectory::Stacks) }, 0 });
-    callback({ "unveil", { fsid, SegmentedProcFSIndex::build_segmented_index_for_main_property_in_pid_directory(pid(), SegmentedProcFSIndex::MainProcessProperty::Unveil) }, 0 });
-    callback({ "pledge", { fsid, SegmentedProcFSIndex::build_segmented_index_for_main_property_in_pid_directory(pid(), SegmentedProcFSIndex::MainProcessProperty::Pledge) }, 0 });
-    callback({ "fds", { fsid, SegmentedProcFSIndex::build_segmented_index_for_main_property_in_pid_directory(pid(), SegmentedProcFSIndex::MainProcessProperty::FileDescriptions) }, 0 });
-    callback({ "exe", { fsid, SegmentedProcFSIndex::build_segmented_index_for_main_property_in_pid_directory(pid(), SegmentedProcFSIndex::MainProcessProperty::BinaryLink) }, 0 });
-    callback({ "cwd", { fsid, SegmentedProcFSIndex::build_segmented_index_for_main_property_in_pid_directory(pid(), SegmentedProcFSIndex::MainProcessProperty::CurrentWorkDirectoryLink) }, 0 });
-    callback({ "perf_events", { fsid, SegmentedProcFSIndex::build_segmented_index_for_main_property_in_pid_directory(pid(), SegmentedProcFSIndex::MainProcessProperty::PerformanceEvents) }, 0 });
-    callback({ "vm", { fsid, SegmentedProcFSIndex::build_segmented_index_for_main_property_in_pid_directory(pid(), SegmentedProcFSIndex::MainProcessProperty::VirtualMemoryStats) }, 0 });
-    callback({ "root", { fsid, SegmentedProcFSIndex::build_segmented_index_for_main_property_in_pid_directory(pid(), SegmentedProcFSIndex::MainProcessProperty::RootLink) }, 0 });
-    return KSuccess;
-}
-
 KResult Process::traverse_stacks_directory(unsigned fsid, Function<bool(FileSystem::DirectoryEntryView const&)> callback) const
 {
     callback({ ".", { fsid, SegmentedProcFSIndex::build_segmented_index_for_main_property(pid(), SegmentedProcFSIndex::ProcessSubDirectory::Stacks, SegmentedProcFSIndex::MainProcessProperty::Reserved) }, 0 });
-    callback({ "..", { fsid, component_index() }, 0 });
+    callback({ "..", { fsid, m_procfs_traits->component_index() }, 0 });
 
     for_each_thread([&](const Thread& thread) {
         int tid = thread.tid().value();
@@ -119,8 +89,8 @@ KResultOr<size_t> Process::procfs_get_file_description_link(unsigned fd, KBuffer
 
 KResult Process::traverse_file_descriptions_directory(unsigned fsid, Function<bool(FileSystem::DirectoryEntryView const&)> callback) const
 {
-    callback({ ".", { fsid, component_index() }, 0 });
+    callback({ ".", { fsid, m_procfs_traits->component_index() }, 0 });
-    callback({ "..", { fsid, component_index() }, 0 });
+    callback({ "..", { fsid, m_procfs_traits->component_index() }, 0 });
     size_t count = 0;
     fds().enumerate([&](auto& file_description_metadata) {
         if (!file_description_metadata.is_valid()) {
@@ -309,7 +279,7 @@ mode_t Process::binary_link_required_mode() const
 {
     if (!executable())
         return 0;
-    return ProcFSExposedComponent::required_mode();
+    return m_procfs_traits->required_mode();
 }
 
 KResult Process::procfs_get_binary_link(KBufferBuilder& builder) const