On Tue, 2007-03-20 at 16:32 +0100, Pierre Peiffer wrote: > Peter Zijlstra a écrit : > >> +static void *get_futex_address(union futex_key *key) > >> +{ > >> + void *uaddr; > >> + > >> + if (key->both.offset & 1) { > >> + /* shared mapping */ > >> + uaddr = (void*)((key->shared.pgoff << PAGE_SHIFT) > >> + + key->shared.offset - 1); > >> + } else { > >> + /* private mapping */ > >> + uaddr = (void*)(key->private.address + key->private.offset); > >> + } > >> + > >> + return uaddr; > >> +} > > > > This will not work for nonlinear vmas, granted, not a lot of ppl stick > > futexes in nonlinear vmas, but the futex_key stuff handles it, this > > doesn't. > > Indeed ! Thanks for pointing me to this. > > Since I'm not familiar with vmm, does this code look more correct to you ?
Unfortunately not, nonlinear vmas don't have a linear relation between address and offset. What you would need to do is do a linear walk of the page tables. But even that might not suffice if nonlinear vmas may form a non-injective, surjective mapping. /me checks.. Hmm, yes that seems valid, so in general, this reverse mapping does not uniquely exist for non-linear vmas. :-( What to do... disallow futexes in nonlinear mappings, store the address in the key? > static void *get_futex_address(union futex_key *key) > { > void *uaddr; > struct vm_area_struct *vma = current->mm->mmap; > > if (key->both.offset & 1) { > /* shared mapping */ > struct file * vmf; > > do { > if ((vmf = vma->vm_file) > && (key->shared.inode == vmf->f_dentry->d_inode)) > break; > vma = vma->vm_next; > } while (vma); > > if (likely(!(vma->vm_flags & VM_NONLINEAR))) > uaddr = (void*)((key->shared.pgoff << PAGE_SHIFT) > + key->shared.offset - 1); > else > uaddr = (void*) vma->vm_start > + ((key->shared.pgoff - vma->vm_pgoff) > << PAGE_SHIFT) > + key->shared.offset - 1; > } else { > /* private mapping */ > uaddr = (void*)(key->private.address + key->private.offset); > } > > return uaddr; > } > > Or is there a more direct way to retrieve the vma corresponding to the given > inode ? the vma_prio_tree would be able to give all vmas associated with a mapping. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/