From d0719efcb4986151cd1e6f87c69a37f9a335fff8 Mon Sep 17 00:00:00 2001
From: Ruihan Li <lrh2000@pku.edu.cn>
Date: Mon, 21 Apr 2025 23:51:16 +0800
Subject: [PATCH] Clarify some API usages

---
 kernel/src/fs/procfs/pid/stat.rs       |  8 ++------
 kernel/src/process/kill.rs             |  2 +-
 kernel/src/process/posix_thread/mod.rs |  2 +-
 kernel/src/process/process/mod.rs      | 25 +++++++++++++++++++------
 4 files changed, 23 insertions(+), 14 deletions(-)

diff --git a/kernel/src/fs/procfs/pid/stat.rs b/kernel/src/fs/procfs/pid/stat.rs
index 99092379..ce483c5c 100644
--- a/kernel/src/fs/procfs/pid/stat.rs
+++ b/kernel/src/fs/procfs/pid/stat.rs
@@ -85,17 +85,13 @@ impl FileOps for StatFileOps {
 
         let pid = process.pid();
         let comm = process.executable_path();
-        let ppid = process.parent().pid();
         let state = if process.status().is_zombie() {
             'Z'
         } else {
             'R'
         };
-        let pgrp = if let Some(pgrp) = process.process_group() {
-            pgrp.pgid()
-        } else {
-            0
-        };
+        let ppid = process.parent().pid();
+        let pgrp = process.pgid();
 
         let mut stat_output = String::new();
         writeln!(
diff --git a/kernel/src/process/kill.rs b/kernel/src/process/kill.rs
index afa3c0f5..c1c1ce2d 100644
--- a/kernel/src/process/kill.rs
+++ b/kernel/src/process/kill.rs
@@ -166,7 +166,7 @@ fn current_thread_sender_ids(signum: Option<&SigNum>, ctx: &Context) -> SignalSe
     let euid = credentials.euid();
     let sid = signum.and_then(|signum| {
         if *signum == SIGCONT {
-            Some(ctx.process.session().unwrap().sid())
+            Some(ctx.process.sid())
         } else {
             None
         }
diff --git a/kernel/src/process/posix_thread/mod.rs b/kernel/src/process/posix_thread/mod.rs
index 1647c8ca..445f9870 100644
--- a/kernel/src/process/posix_thread/mod.rs
+++ b/kernel/src/process/posix_thread/mod.rs
@@ -149,7 +149,7 @@ impl PosixThread {
         if let Some(signum) = signum
             && *signum == SIGCONT
         {
-            let receiver_sid = self.process().session().unwrap().sid();
+            let receiver_sid = self.process().sid();
             if receiver_sid == sender.sid().unwrap() {
                 return Ok(());
             }
diff --git a/kernel/src/process/process/mod.rs b/kernel/src/process/process/mod.rs
index 313c8b6f..15b7b54b 100644
--- a/kernel/src/process/process/mod.rs
+++ b/kernel/src/process/process/mod.rs
@@ -344,11 +344,6 @@ impl Process {
 
     // *********** Process group & Session ***********
 
-    /// Returns the process group to which the process belongs.
-    pub fn process_group(&self) -> Option<Arc<ProcessGroup>> {
-        self.process_group.lock().upgrade()
-    }
-
     /// Returns the process group ID of the process.
     //
     // FIXME: If we call this method without holding the process table lock, it may return zero if
@@ -365,9 +360,27 @@ impl Process {
         self.session().map_or(0, |session| session.sid())
     }
 
+    /// Returns the process group to which the process belongs.
+    ///
+    /// **Deprecated:** This is a very poorly designed API. Almost every use of this API is wrong
+    /// because some race condition is not handled correctly. Such usages are being refactored and
+    /// this API will be removed soon. So DO NOT ATTEMPT TO USE THIS API IN NEW CODE unless you
+    /// know exactly what you're doing.
+    pub fn process_group(&self) -> Option<Arc<ProcessGroup>> {
+        self.process_group.lock().upgrade()
+    }
+
     /// Returns the session to which the process belongs.
+    ///
+    /// **Deprecated:** This is a very poorly designed API. Almost every use of this API is wrong
+    /// because some race condition is not handled correctly. Such usages are being refactored and
+    /// this API will be removed soon. So DO NOT ATTEMPT TO USE THIS API IN NEW CODE unless you
+    /// know exactly what you're doing.
     pub fn session(&self) -> Option<Arc<Session>> {
-        self.process_group()?.session()
+        self.process_group
+            .lock()
+            .upgrade()
+            .and_then(|group| group.session())
     }
 
     /// Returns whether the process is session leader.