Messages in this thread Patch in this message | | | Date | Fri, 30 Jan 2009 10:14:26 -0800 (PST) | From | Linus Torvalds <> | Subject | Re: [PATCH] Fix OOPS in mmap_region() when merging adjacent VM_LOCKED file segments |
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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
--- 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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