mlock: operate on any regions with protection != PROT_NONE
As Tao Ma noticed, change5ecfda0
breaks blktrace. This is because blktrace mmaps a file with PROT_WRITE permissions but without PROT_READ, so my attempt to not unnecessarity break COW during mlock ended up causing mlock to fail with a permission problem. I am proposing to let mlock ignore vma protection in all cases except PROT_NONE. In particular, mlock should not fail for PROT_WRITE regions (as in the blktrace case, which broke at5ecfda0
) or for PROT_EXEC regions (which seem to me like they were always broken). Signed-off-by: Michel Lespinasse <walken@google.com> Acked-by: Rik van Riel <riel@redhat.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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@ -178,6 +178,13 @@ static long __mlock_vma_pages_range(struct vm_area_struct *vma,
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if ((vma->vm_flags & (VM_WRITE | VM_SHARED)) == VM_WRITE)
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gup_flags |= FOLL_WRITE;
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/*
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* We want mlock to succeed for regions that have any permissions
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* other than PROT_NONE.
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*/
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if (vma->vm_flags & (VM_READ | VM_WRITE | VM_EXEC))
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gup_flags |= FOLL_FORCE;
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if (vma->vm_flags & VM_LOCKED)
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gup_flags |= FOLL_MLOCK;
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