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); > > +} -- Sincerely yours, Mike.