Re: [PATCH 2.6.13.1] Patch for invisible threads

[Sripathi Kodi <sripathik@in.ibm.com>]

Linus Torvalds wrote:

> I don't think this is wrong per se, but you shouldn't take the tasklist 
> lock normally. You're better off just doing

Linus,

I incarporated the path that doesn't hold tasklist lock unnecessarily. The 
patch is below. This seems to work without any problems for me.

If the decision is to remove ->permission, I can send a small patch I have 
that removes .permission entry from proc_task_inode_operations. Either way 
fixes the problem I found.

Thanks and regards,
Sripathi.

Signed-off-by: Sripathi Kodi <sripathik@in.ibm.com>

--- linux-2.6.13.1-orig/fs/proc/base.c	2005-09-14 03:46:22.000000000 -0500
+++ linux-2.6.13.1/fs/proc/base.c	2005-09-14 03:48:35.000000000 -0500
@@ -275,11 +275,33 @@ static int proc_root_link(struct inode *
  {
  	struct fs_struct *fs;
  	int result = -ENOENT;
-	task_lock(proc_task(inode));
-	fs = proc_task(inode)->fs;
-	if(fs)
+	struct task_struct *leader = proc_task(inode);
+
+	task_lock(leader);
+	fs = leader->fs;
+	if (fs) {
  		atomic_inc(&fs->count);
-	task_unlock(proc_task(inode));
+		task_unlock(leader);
+	} else {
+		/* Try to get fs from sub-threads */
+		task_unlock(leader);
+		struct task_struct *task = leader;
+		read_lock(&tasklist_lock);
+		if (pid_alive(task)) {
+			while ((task = next_thread(task)) != leader) {
+				task_lock(task);
+				fs = task->fs;
+				if (fs) {
+					atomic_inc(&fs->count);
+					task_unlock(task);
+					break;
+				}
+				task_unlock(task);
+			}
+		}
+		read_unlock(&tasklist_lock);
+	}
+
  	if (fs) {
  		read_lock(&fs->lock);
  		*mnt = mntget(fs->rootmnt);