Re: [PATCH] sys_remap_file_pages: fix ->vm_file accounting

[Matt Helsley <matthltc@us.ibm.com>]

On Wed, 2008-01-30 at 20:26 +0300, Oleg Nesterov wrote:
> On 01/30, Miklos Szeredi wrote:
> > 
> > On Wed, 2008-01-30 at 17:20 +0300, Oleg Nesterov wrote:
> > > Fix ->vm_file accounting, mmap_region() may do do_munmap().
> > 
> > There's a small problem with the patch: the vma itself is freed at
> > unmap, so the fput(vma->vm_file) may crash.  Here's an updated patch.
> 
> Ah, indeed, thanks!
> 
> 
> Offtopic. I noticed this problem while looking at this patch:
> 
> 	http://marc.info/?l=linux-mm-commits&m=120141116911711
> 
> So this (the old vma could be removed before we create the new mapping)
> means that the patch above has another problem: if we are remapping the
> whole VM_EXECUTABLE vma, removed_exe_file_vma() can clear ->exe_file
> while it shouldn't (Matt Helsley cc'ed).
> 
> Oleg.

Only shared VMAs can be remapped by sys_remap_file_pages but all
executable mappings are MAP_PRIVATE and hence lack the shared flag. I
don't know of a way for userspace to change that flag so I think there's
nothing that needs to be done here.

Cc'ing linux-mm.

Cheers,
	-Matt Helsley

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>