From patchwork Tue Dec 31 18:11:49 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Eric Biggers X-Patchwork-Id: 11314353 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 6FB8214BD for ; Tue, 31 Dec 2019 18:12:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4E09F206E4 for ; Tue, 31 Dec 2019 18:12:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1577815938; bh=3w6Tqz6ueWQmYAc9y5MHb7VV8NOhy18y1NXJnrZB9r4=; h=From:To:Cc:Subject:Date:List-ID:From; b=zpEJXv4Kn5MrSWnbh4/+1RYhB7SrWyf9RWHIUjOQNeXaqUdejlB8aeWDt4bsDQhfD yuBcA1IPEClRRNdmlR8HnGEO1wLRJDWzjBg7NVZFxxIxZrIADUx86AMV0afJ+AHJzt PZwQoLiJHe50XlXwyjBBJnK01UoKGNFfS47gERWI= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727082AbfLaSMS (ORCPT ); Tue, 31 Dec 2019 13:12:18 -0500 Received: from mail.kernel.org ([198.145.29.99]:49866 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726720AbfLaSMR (ORCPT ); Tue, 31 Dec 2019 13:12:17 -0500 Received: from zzz.tds (h75-100-12-111.burkwi.broadband.dynamic.tds.net [75.100.12.111]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 24A47206DB; Tue, 31 Dec 2019 18:12:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1577815937; bh=3w6Tqz6ueWQmYAc9y5MHb7VV8NOhy18y1NXJnrZB9r4=; h=From:To:Cc:Subject:Date:From; b=Mm7U13xEQY5R5VLNawwgv+UDO4Tm4+clvpIvNgQ0Z6WzzaxNryKCWzxK3GBqQJbon zkaDer0HqvI2MzaIRucQbcGBXAjDnVfAbPLfegUWCrIRLENmrmCliulKydCsnRkdAc 19NbdsrFbO/DQHo2r2YJAiACHxGc6JZipqHFYFJ0= From: Eric Biggers To: linux-ext4@vger.kernel.org Cc: linux-fscrypt@vger.kernel.org Subject: [PATCH] ext4: fix deadlock allocating crypto bounce page from mempool Date: Tue, 31 Dec 2019 12:11:49 -0600 Message-Id: <20191231181149.47619-1-ebiggers@kernel.org> X-Mailer: git-send-email 2.24.1 MIME-Version: 1.0 Sender: linux-fscrypt-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fscrypt@vger.kernel.org From: Eric Biggers ext4_writepages() on an encrypted file has to encrypt the data, but it can't modify the pagecache pages in-place, so it encrypts the data into bounce pages and writes those instead. All bounce pages are allocated from a mempool using GFP_NOFS. This is not correct use of a mempool, and it can deadlock. This is because GFP_NOFS includes __GFP_DIRECT_RECLAIM, which enables the "never fail" mode for mempool_alloc() where a failed allocation will fall back to waiting for one of the preallocated elements in the pool. But since this mode is used for all a bio's pages and not just the first, it can deadlock waiting for pages already in the bio to be freed. This deadlock can be reproduced by patching mempool_alloc() to pretend that pool->alloc() always fails (so that it always falls back to the preallocations), and then creating an encrypted file of size > 128 KiB. Fix it by only using GFP_NOFS for the first page in the bio. For subsequent pages just use GFP_NOWAIT, and if any of those fail, just submit the bio and start a new one. This will need to be fixed in f2fs too, but that's less straightforward. Fixes: c9af28fdd449 ("ext4 crypto: don't let data integrity writebacks fail with ENOMEM") Cc: stable@vger.kernel.org Signed-off-by: Eric Biggers --- fs/ext4/page-io.c | 19 ++++++++++++++----- 1 file changed, 14 insertions(+), 5 deletions(-) diff --git a/fs/ext4/page-io.c b/fs/ext4/page-io.c index 24aeedb8fc75..68b39e75446a 100644 --- a/fs/ext4/page-io.c +++ b/fs/ext4/page-io.c @@ -512,17 +512,26 @@ int ext4_bio_write_page(struct ext4_io_submit *io, gfp_t gfp_flags = GFP_NOFS; unsigned int enc_bytes = round_up(len, i_blocksize(inode)); + /* + * Since bounce page allocation uses a mempool, we can only use + * a waiting mask (i.e. request guaranteed allocation) on the + * first page of the bio. Otherwise it can deadlock. + */ + if (io->io_bio) + gfp_flags = GFP_NOWAIT | __GFP_NOWARN; retry_encrypt: bounce_page = fscrypt_encrypt_pagecache_blocks(page, enc_bytes, 0, gfp_flags); if (IS_ERR(bounce_page)) { ret = PTR_ERR(bounce_page); - if (ret == -ENOMEM && wbc->sync_mode == WB_SYNC_ALL) { - if (io->io_bio) { + if (ret == -ENOMEM && + (io->io_bio || wbc->sync_mode == WB_SYNC_ALL)) { + gfp_flags = GFP_NOFS; + if (io->io_bio) ext4_io_submit(io); - congestion_wait(BLK_RW_ASYNC, HZ/50); - } - gfp_flags |= __GFP_NOFAIL; + else + gfp_flags |= __GFP_NOFAIL; + congestion_wait(BLK_RW_ASYNC, HZ/50); goto retry_encrypt; }