Messages in this thread |  | | | Date | Fri, 30 Jan 2009 18:30:59 +0000 (GMT) | | From | Hugh Dickins <> | | Subject | Re: [PATCH] Fix OOPS in mmap_region() when merging adjacent VM_LOCKED file segments |
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On Fri, 30 Jan 2009, Linus Torvalds wrote: > On Fri, 30 Jan 2009, Hugh Dickins wrote: > > > > ... what I think you have done is break the vma merging on > > ordinary files: because of that irritating VM_CAN_NONLINEAR > > flag which generic_file_mmap() and some others add in. > > Ahh. Yes. VM_CAN_NONLINEAR is a "reverse flag", ie unlike the other flags > it's to some degree about being extra _normal_, not about being odd. Most > special flags tend to disable the VM from doing some clever thing, this > one enables it. > > > To break the merging won't cause anyone much trouble, > > but is a slight regression we should fix. > > Yeah. Just masking it off when comparing is probably the simplest option. > Make it a separate #define just for readability. There might be other > flags like this in the future. > > > I'd have been very upset not to find something ;) > > Yay for you ;) > > And yes, this is the kind of thing that probably does mean that we're > better off with the no-semantic-changes patches in -stable. > > Linus
Yes, your patch looks just right to me - or maybe add a comment that it's only mmap_region()'s call to vma_merge() which needs that mask?
If you hear no more from me, that'll be all I found.
Hugh
> > --- > mm/mmap.c | 5 ++++- > 1 files changed, 4 insertions(+), 1 deletions(-) > > diff --git a/mm/mmap.c b/mm/mmap.c > index d3fa10a..c581df1 100644 > --- a/mm/mmap.c > +++ b/mm/mmap.c > @@ -658,6 +658,9 @@ again: remove_next = 1 + (end > next->vm_end); > validate_mm(mm); > } > > +/* Flags that can be inherited from an existing mapping when merging */ > +#define VM_MERGEABLE_FLAGS (VM_CAN_NONLINEAR) > + > /* > * If the vma has a ->close operation then the driver probably needs to release > * per-vma resources, so we don't attempt to merge those. > @@ -665,7 +668,7 @@ again: remove_next = 1 + (end > next->vm_end); > static inline int is_mergeable_vma(struct vm_area_struct *vma, > struct file *file, unsigned long vm_flags) > { > - if (vma->vm_flags != vm_flags) > + if ((vma->vm_flags ^ vm_flags) & ~VM_MERGEABLE_FLAGS) > return 0; > if (vma->vm_file != file) > return 0;
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