On Wed, Jan 20, 2021 at 04:02:10PM +0000, Matthew Wilcox wrote:

On Wed, Jan 20, 2021 at 05:05:10PM +0200, Mike Rapoport wrote:

quoted

On Tue, Jan 19, 2021 at 08:22:13PM +0000, Matthew Wilcox wrote:

quoted

On Thu, Dec 03, 2020 at 08:29:44AM +0200, Mike Rapoport wrote:

quoted

+static vm_fault_t secretmem_fault(struct vm_fault *vmf)
+{
+	struct address_space *mapping = vmf->vma->vm_file->f_mapping;
+	struct inode *inode = file_inode(vmf->vma->vm_file);
+	pgoff_t offset = vmf->pgoff;
+	vm_fault_t ret = 0;
+	unsigned long addr;
+	struct page *page;
+	int err;
+
+	if (((loff_t)vmf->pgoff << PAGE_SHIFT) >= i_size_read(inode))
+		return vmf_error(-EINVAL);
+
+	page = find_get_page(mapping, offset);
+	if (!page) {
+
+		page = secretmem_alloc_page(vmf->gfp_mask);
+		if (!page)
+			return vmf_error(-ENOMEM);

Just use VM_FAULT_OOM directly.

 
Ok.

quoted

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+		err = add_to_page_cache(page, mapping, offset, vmf->gfp_mask);
+		if (unlikely(err))
+			goto err_put_page;

What if the error is EEXIST because somebody else raced with you to add
a new page to the page cache?

Right, for -EEXIST I need a retry here, thanks.

quoted

quoted

+		err = set_direct_map_invalid_noflush(page, 1);
+		if (err)
+			goto err_del_page_cache;

Does this work correctly if somebody else has a reference to the page
in the meantime?

Yes, it does. If somebody else won the race that page was dropped from the
direct map and this call would be essentially a nop. And anyway, the very
next patch changes the way pages are removed from the direct map ;-)

What I'm thinking is:

thread A page faults
doesn't find page
allocates page
adds page to page cache
				thread B page faults
				does find page in page cache
set direct map invalid fails
deletes from page cache
				... ?

Hmm, this is not nice indeed...

-- 
Sincerely yours,
Mike.