On Tue, Jan 19, 2021 at 08:22:13PM +0000, Matthew Wilcox wrote:
On Thu, Dec 03, 2020 at 08:29:44AM +0200, Mike Rapoport wrote:
+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.
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.
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 ;-)
addr = (unsigned long)page_address(page);flush_tlb_kernel_range(addr, addr + PAGE_SIZE);__SetPageUptodate(page);Once you've added it to the cache, somebody else can come along and try to lock it. They will set PageWaiter. Now you call __SetPageUptodate and wipe out their PageWaiter bit. So you won't wake them up when you unlock.
You can call __SetPageUptodate before adding it to the page cache, but once it's visible to another thread, you can't do that.
Will fix.
ret = VM_FAULT_LOCKED;- }
- vmf->page = page;
You're supposed to return the page locked, so use find_lock_page() instead of find_get_page().
Ok/
- return ret;
+err_del_page_cache:
- delete_from_page_cache(page);
+err_put_page:
- put_page(page);
- return vmf_error(err);
+}