Re: [RFC][PATCH 1/3] [RFC][PATCH] Fix procfs task exe symlinks

Matt Helsley
2007-11-01T19:53:17Z

On Thu, 2007-11-01 at 12:25 -0700, Andrew Morton wrote:
> On Wed, 31 Oct 2007 20:35:09 -0700
> Matt Helsley <matthltc@us.ibm.com> wrote:
>
> > +++ linux-2.6.23/include/linux/sched.h
> > @@ -430,10 +430,13 @@ struct mm_struct {
> > struct completion *core_startup_done, core_done;
> >
> > /* aio bits */
> > rwlock_t ioctx_list_lock;
> > struct kioctx *ioctx_list;
> > +
> > + /* store ref to file /proc/<pid>/exe symlink points to */
> > + struct file *exe_file;
> > };
>
> I guess with a little work this could be made conditional on
> CONFIG_PROC_FS. ie: change get_mm_exe_file() to

Sorry, I thought ifdefs were generally frowned upon in structs. I'll add
them here and make sure everthing still works properly.

> void get_mm_exe_file(struct mm_struct *newmm, struct mm_struct *old_mm);
>
> > @@ -1716,10 +1744,14 @@ static void remove_vma_list(struct mm_st
> >
> > mm->total_vm -= nrpages;
> > if (vma->vm_flags & VM_LOCKED)
> > mm->locked_vm -= nrpages;
> > vm_stat_account(mm, vma->vm_flags, vma->vm_file, -nrpages);
> > + if (mm->exe_file && (vma->vm_file == mm->exe_file)) {
> > + fput(mm->exe_file);
> > + mm->exe_file = NULL;
> > + }
> > vma = remove_vma(vma);
> > } while (vma);
> > validate_mm(mm);
> > }
>
> hm, fput() while holding mmap_sem. I wonder if that's a problem.
>
> I assume you've runtime tested this with lockdep enabled, but fput() is one
> of those funny things which can call all sorts of things which one least
> expects and where testers hit things which developers don't.

It's being used under the mmap semaphore in remove_vma() so, even if
fput() with mmap_sem held is a bug, I'm not introducing any new bugs :).

Thanks,
-Matt Helsley