[Devel] [RFC][PATCH 07/16] Move alloc_pid call to copy_process

[sukadev at us.ibm.com]

Subject: Move alloc_pid call to copy_process

From: Sukadev Bhattiprolu <sukadev at us.ibm.com>

Move alloc_pid() into copy_process(). This will keep all pid and pid
namespace code together and simplify error handling when we support
multiple pid namespaces.

Changelog: 
	- [Eric Biederman] Move the check of copy_process_type to alloc_pid()/
	  free_pid() and to avoid clutter in copy_process().

Signed-off-by: Sukadev Bhattiprolu <sukadev at us.ibm.com>
---
 include/linux/pid.h |    7 ++++++-
 kernel/fork.c       |   21 +++++++++++++--------
 kernel/pid.c        |   10 +++++++++-
 3 files changed, 28 insertions(+), 10 deletions(-)

Index: lx26-21-mm2/include/linux/pid.h
===================================================================
--- lx26-21-mm2.orig/include/linux/pid.h	2007-05-22 16:59:40.000000000 -0700
+++ lx26-21-mm2/include/linux/pid.h	2007-05-22 17:06:48.000000000 -0700
@@ -3,6 +3,11 @@
 
 #include <linux/rcupdate.h>
 
+enum copy_process_type {
+	COPY_NON_IDLE_PROCESS,
+	COPY_IDLE_PROCESS,
+};
+
 enum pid_type
 {
 	PIDTYPE_PID,
@@ -95,7 +100,7 @@ extern struct pid *FASTCALL(find_pid(int
 extern struct pid *find_get_pid(int nr);
 extern struct pid *find_ge_pid(int nr);
 
-extern struct pid *alloc_pid(void);
+extern struct pid *alloc_pid(enum copy_process_type);
 extern void FASTCALL(free_pid(struct pid *pid));
 
 static inline pid_t pid_to_nr(struct pid *pid)
Index: lx26-21-mm2/kernel/fork.c
===================================================================
--- lx26-21-mm2.orig/kernel/fork.c	2007-05-22 16:59:41.000000000 -0700
+++ lx26-21-mm2/kernel/fork.c	2007-05-22 17:06:48.000000000 -0700
@@ -961,10 +961,11 @@ static struct task_struct *copy_process(
 					unsigned long stack_size,
 					int __user *parent_tidptr,
 					int __user *child_tidptr,
-					struct pid *pid)
+					enum copy_process_type copy_src)
 {
 	int retval;
 	struct task_struct *p = NULL;
+	struct pid *pid;
 
 	if ((clone_flags & (CLONE_NEWNS|CLONE_FS)) == (CLONE_NEWNS|CLONE_FS))
 		return ERR_PTR(-EINVAL);
@@ -1025,6 +1026,10 @@ static struct task_struct *copy_process(
 	if (p->binfmt && !try_module_get(p->binfmt->module))
 		goto bad_fork_cleanup_put_domain;
 
+	pid = alloc_pid(copy_src);
+	if (!pid)
+		goto bad_fork_put_binfmt_module;
+
 	p->did_exec = 0;
 	delayacct_tsk_init(p);	/* Must remain after dup_task_struct() */
 	copy_flags(clone_flags, p);
@@ -1305,6 +1310,8 @@ bad_fork_cleanup_cpuset:
 #endif
 	cpuset_exit(p);
 	delayacct_tsk_free(p);
+	free_pid(pid);
+bad_fork_put_binfmt_module:
 	if (p->binfmt)
 		module_put(p->binfmt->module);
 bad_fork_cleanup_put_domain:
@@ -1331,7 +1338,7 @@ struct task_struct * __cpuinit fork_idle
 	struct pt_regs regs;
 
 	task = copy_process(CLONE_VM, 0, idle_regs(&regs), 0, NULL, NULL,
-				&init_struct_pid);
+				COPY_IDLE_PROCESS);
 	if (!IS_ERR(task))
 		init_idle(task, cpu);
 
@@ -1369,19 +1376,16 @@ long do_fork(unsigned long clone_flags,
 {
 	struct task_struct *p;
 	int trace = 0;
-	struct pid *pid = alloc_pid();
 	long nr;
 
-	if (!pid)
-		return -EAGAIN;
-	nr = pid->nr;
 	if (unlikely(current->ptrace)) {
 		trace = fork_traceflag (clone_flags);
 		if (trace)
 			clone_flags |= CLONE_PTRACE;
 	}
 
-	p = copy_process(clone_flags, stack_start, regs, stack_size, parent_tidptr, child_tidptr, pid);
+	p = copy_process(clone_flags, stack_start, regs, stack_size,
+			parent_tidptr, child_tidptr, COPY_NON_IDLE_PROCESS);
 	/*
 	 * Do this prior waking up the new thread - the thread pointer
 	 * might get invalid after that point, if the thread exits quickly.
@@ -1389,6 +1393,8 @@ long do_fork(unsigned long clone_flags,
 	if (!IS_ERR(p)) {
 		struct completion vfork;
 
+		nr = pid_to_nr(task_pid(p));
+
 		if (clone_flags & CLONE_VFORK) {
 			p->vfork_done = &vfork;
 			init_completion(&vfork);
@@ -1422,7 +1428,6 @@ long do_fork(unsigned long clone_flags,
 			}
 		}
 	} else {
-		free_pid(pid);
 		nr = PTR_ERR(p);
 	}
 	return nr;
Index: lx26-21-mm2/kernel/pid.c
===================================================================
--- lx26-21-mm2.orig/kernel/pid.c	2007-05-22 16:59:46.000000000 -0700
+++ lx26-21-mm2/kernel/pid.c	2007-05-22 17:06:48.000000000 -0700
@@ -216,6 +216,10 @@ fastcall void free_pid(struct pid *pid)
 	/* We can be called with write_lock_irq(&tasklist_lock) held */
 	unsigned long flags;
 
+	/* check this here to keep copy_process() cleaner */
+	if (unlikely(pid == &init_struct_pid))
+		return;
+
 	spin_lock_irqsave(&pidmap_lock, flags);
 	hlist_del_rcu(&pid->pid_chain);
 	spin_unlock_irqrestore(&pidmap_lock, flags);
@@ -224,12 +228,16 @@ fastcall void free_pid(struct pid *pid)
 	call_rcu(&pid->rcu, delayed_put_pid);
 }
 
-struct pid *alloc_pid(void)
+struct pid *alloc_pid(enum copy_process_type copy_src)
 {
 	struct pid *pid;
 	enum pid_type type;
 	int nr = -1;
 
+	/* check this here to keep copy_process() cleaner */
+	if (unlikely(copy_src == COPY_IDLE_PROCESS))
+		return &init_struct_pid;
+
 	pid = kmem_cache_alloc(pid_cachep, GFP_KERNEL);
 	if (!pid)
 		goto out;
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