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: > > 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 ;-) > > 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.