On Thu, 14 May 2015 19:31:19 +0200 Andrea Arcangeli <aarcange@xxxxxxxxxx> wrote:
> If the rwsem starves writers it wasn't strictly a bug but lockdep
> doesn't like it and this avoids depending on lowlevel implementation
> details of the lock.
>
> ...
>
> @@ -229,13 +246,33 @@ static __always_inline ssize_t __mcopy_atomic(struct mm_struct *dst_mm,
>
> if (!zeropage)
> err = mcopy_atomic_pte(dst_mm, dst_pmd, dst_vma,
> - dst_addr, src_addr);
> + dst_addr, src_addr, &page);
> else
> err = mfill_zeropage_pte(dst_mm, dst_pmd, dst_vma,
> dst_addr);
>
> cond_resched();
>
> + if (unlikely(err == -EFAULT)) {
> + void *page_kaddr;
> +
> + BUILD_BUG_ON(zeropage);
I'm not sure what this is trying to do. BUILD_BUG_ON(local_variable)?
It goes bang in my build. I'll just delete it.
> + up_read(&dst_mm->mmap_sem);
> + BUG_ON(!page);
> +
> + page_kaddr = kmap(page);
> + err = copy_from_user(page_kaddr,
> + (const void __user *) src_addr,
> + PAGE_SIZE);
> + kunmap(page);
> + if (unlikely(err)) {
> + err = -EFAULT;
> + goto out;
> + }
> + goto retry;
> + } else
> + BUG_ON(page);
> +
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