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

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Date:	Thu, 01 Nov 2007 12:52:56 -0700
From:	Matt Helsley <matthltc@...ibm.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	viro@....linux.org.uk, haveblue@...ibm.com
Subject: Re: [RFC][PATCH 1/3] [RFC][PATCH] Fix procfs task exe symlinks

On Thu, 2007-11-01 at 12:25 -0700, Andrew Morton wrote:
> On Wed, 31 Oct 2007 20:35:09 -0700
> Matt Helsley <matthltc@...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


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