[PATCH 2/2] proc: rewrite next_tgid()

[Alexey Dobriyan <adobriyan@gmail.com>]

* deduplicate "iter.tgid += 1" line,
  Right now it is done once inside next_tgid() itself and second time
  inside "for" loop.

* deduplicate next_tgid() call itself with different loop style:

	auto it = make_tgid_iter();
	while (next_tgid(&it)) {
		...
	}

  gcc seems to inline it twice:

  	$ ./scripts/bloat-o-meter ../vmlinux-000 ../obj/vmlinux
	add/remove: 0/1 grow/shrink: 1/0 up/down: 100/-245 (-145)
	Function                                     old     new   delta
	proc_pid_readdir                             531     631    +100
	next_tgid                                    245       -    -245

* make tgid_iter.pid_ns const
  it never changes during readdir anyway
---
 fs/proc/base.c | 57 +++++++++++++++++++++++++++++---------------------
 1 file changed, 33 insertions(+), 24 deletions(-)

diff --git a/fs/proc/base.c b/fs/proc/base.c
index f2db455dbbfd..f38ac943ec32 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -3543,30 +3543,43 @@ struct dentry *proc_pid_lookup(struct dentry *dentry, unsigned int flags)
 struct tgid_iter {
 	unsigned int tgid;
 	struct task_struct *task;
-	struct pid_namespace *pid_ns;
+	struct pid_namespace *const pid_ns;
 };
 
-static struct tgid_iter next_tgid(struct tgid_iter iter)
+static
+struct tgid_iter
+make_tgid_iter(unsigned int init_tgid, struct pid_namespace *pid_ns)
 {
-	struct pid *pid;
+	return (struct tgid_iter){
+		.tgid = init_tgid - 1,
+		.pid_ns = pid_ns,
+	};
+}
+
+static bool next_tgid(struct tgid_iter *it)
+{
+	if (it->task) {
+		put_task_struct(it->task);
+		it->task = NULL;
+	}
 
-	if (iter.task)
-		put_task_struct(iter.task);
 	rcu_read_lock();
-retry:
-	iter.task = NULL;
-	pid = find_ge_pid(iter.tgid, iter.pid_ns);
-	if (pid) {
-		iter.tgid = pid_nr_ns(pid, iter.pid_ns);
-		iter.task = pid_task(pid, PIDTYPE_TGID);
-		if (!iter.task) {
-			iter.tgid += 1;
-			goto retry;
+	while (1) {
+		it->tgid += 1;
+		const auto pid = find_ge_pid(it->tgid, it->pid_ns);
+		if (pid) {
+			it->tgid = pid_nr_ns(pid, it->pid_ns);
+			it->task = pid_task(pid, PIDTYPE_TGID);
+			if (it->task) {
+				get_task_struct(it->task);
+				rcu_read_unlock();
+				return true;
+			}
+		} else {
+			rcu_read_unlock();
+			return false;
 		}
-		get_task_struct(iter.task);
 	}
-	rcu_read_unlock();
-	return iter;
 }
 
 #define TGID_OFFSET (FIRST_PROCESS_ENTRY + 2)
@@ -3574,7 +3587,6 @@ static struct tgid_iter next_tgid(struct tgid_iter iter)
 /* for the /proc/ directory itself, after non-process stuff has been done */
 int proc_pid_readdir(struct file *file, struct dir_context *ctx)
 {
-	struct tgid_iter iter;
 	struct proc_fs_info *fs_info = proc_sb_info(file_inode(file)->i_sb);
 	struct pid_namespace *pid_ns = proc_pid_ns(file_inode(file)->i_sb);
 	loff_t pos = ctx->pos;
@@ -3592,12 +3604,9 @@ int proc_pid_readdir(struct file *file, struct dir_context *ctx)
 			return 0;
 		ctx->pos = pos = pos + 1;
 	}
-	iter.tgid = pos - TGID_OFFSET;
-	iter.task = NULL;
-	iter.pid_ns = pid_ns;
-	for (iter = next_tgid(iter);
-	     iter.task;
-	     iter.tgid += 1, iter = next_tgid(iter)) {
+
+	auto iter = make_tgid_iter(pos - TGID_OFFSET, pid_ns);
+	while (next_tgid(&iter)) {
 		char name[10 + 1];
 		unsigned int len;
 
-- 
2.52.0