On Tue, May 22, 2007 at 11:29:51AM -0700, Andrew Morton wrote:
> On Tue, 22 May 2007 21:43:49 +0400
> Alexey Dobriyan <[email protected]> wrote:
>
> > On Sun, May 20, 2007 at 08:41:02PM -0700, [email protected] wrote:
> > > Subject: procfs directory entry cleanup
> > > From: "Changli Gao" <[email protected]>
> > >
> > > Function proc_register() will assign proc_dir_operations and
> > > proc_dir_inode_operations to ent's members proc_fops and proc_iops
> > > correctly if ent is a directory. So the early assignment isn't
> > > necessary.
> >
> > > --- a/fs/proc/generic.c~procfs-directory-entry-cleanup
> > > +++ a/fs/proc/generic.c
> > > @@ -649,9 +649,6 @@ struct proc_dir_entry *proc_mkdir_mode(c
> > >
> > > ent = proc_create(&parent, name, S_IFDIR | mode, 2);
> > > if (ent) {
> > > - ent->proc_fops = &proc_dir_operations;
> > > - ent->proc_iops = &proc_dir_inode_operations;
> > > -
> > > if (proc_register(parent, ent) < 0) {
> > > kfree(ent);
> > > ent = NULL;
> > > @@ -686,10 +683,6 @@ struct proc_dir_entry *create_proc_entry
> > >
> > > ent = proc_create(&parent,name,mode,nlink);
> > > if (ent) {
> > > - if (S_ISDIR(mode)) {
> > > - ent->proc_fops = &proc_dir_operations;
> > > - ent->proc_iops = &proc_dir_inode_operations;
> > > - }
> > > if (proc_register(parent, ent) < 0) {
> > > kfree(ent);
> > > ent = NULL;
> >
> > This should add race because new PDE for directory will be glued to tree
> > with NULL ->proc_iops and, at least, vfs_getattr() doesn't check for
> > NULL ->i_op.
> >
> > I've tried to reproduce this scenario with udelay() inserted before
> > S_ISDIR checks in proc_register() but got some panic while in X,
> > so no cookie for me. Maybe it's impossible, indeed.
> >
> > Anyway, this patch + moving ->proc_fops and ->proc_iops initialization
> > before gluing is OK with me.
>
> Like this?
Yes, exactly.
> --- a/fs/proc/generic.c~procfs-directory-entry-cleanup-fix
> +++ a/fs/proc/generic.c
> @@ -529,12 +529,6 @@ static int proc_register(struct proc_dir
> return -EAGAIN;
> dp->low_ino = i;
>
> - spin_lock(&proc_subdir_lock);
> - dp->next = dir->subdir;
> - dp->parent = dir;
> - dir->subdir = dp;
> - spin_unlock(&proc_subdir_lock);
> -
> if (S_ISDIR(dp->mode)) {
> if (dp->proc_iops == NULL) {
> dp->proc_fops = &proc_dir_operations;
> @@ -550,6 +544,13 @@ static int proc_register(struct proc_dir
> if (dp->proc_iops == NULL)
> dp->proc_iops = &proc_file_inode_operations;
> }
> +
> + spin_lock(&proc_subdir_lock);
> + dp->next = dir->subdir;
> + dp->parent = dir;
> + dir->subdir = dp;
> + spin_unlock(&proc_subdir_lock);
> +
> return 0;
> }
>
> _
-
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