From patchwork Fri Oct 11 15:41:20 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Filipe Manana X-Patchwork-Id: 11185763 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 F08D218B7 for ; Fri, 11 Oct 2019 15:41:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D24BD21D71 for ; Fri, 11 Oct 2019 15:41:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1570808502; bh=K6QDyckbXgjWdYMdc/J7V++QIPJcDaEWoSfporUFoQA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=D+GYyA/MpUET22lM2KzZMDucvbUuGBcaCtUquSt18BPHQN4L3UKiBBuf2Keh2vS2l ILF7kUfkSVIN3NSg0Xh/q4gRSnMTpBYYkC+60UHAUymtcQAlCcM+Kjh43V0MU4QXIm F2XqEo6iMb8TSW5bz51y2G3ho2KNkDmsFou+erqI= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727932AbfJKPlm (ORCPT ); Fri, 11 Oct 2019 11:41:42 -0400 Received: from mail.kernel.org ([198.145.29.99]:57504 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726642AbfJKPll (ORCPT ); Fri, 11 Oct 2019 11:41:41 -0400 Received: from localhost.localdomain (bl8-197-74.dsl.telepac.pt [85.241.197.74]) (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 DE5AC206A1; Fri, 11 Oct 2019 15:41:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1570808500; bh=K6QDyckbXgjWdYMdc/J7V++QIPJcDaEWoSfporUFoQA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=M/SC0GiBWoxYLZTDA8wtgZfRnXd9a/qe5lblacJEMt8zJxlvBnKjF8RdEZytoskEI gYFucRDEpkMofnstjTsIvdDzraEzvbwtKD9uQpUnRLQ4NIReWgQtR3AMzR5NuJgrwX WOojcOIlkyRe5FmiJYb/0Myp+3HNEkplUzGdWNec= From: fdmanana@kernel.org To: linux-btrfs@vger.kernel.org Cc: josef@toxicpanda.com, Filipe Manana Subject: [PATCH v2] Btrfs: fix negative subv_writers counter and data space leak after buffered write Date: Fri, 11 Oct 2019 16:41:20 +0100 Message-Id: <20191011154120.5547-1-fdmanana@kernel.org> X-Mailer: git-send-email 2.11.0 In-Reply-To: <20191009164422.7202-1-fdmanana@kernel.org> References: <20191009164422.7202-1-fdmanana@kernel.org> Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org From: Filipe Manana When doing a buffered write it's possible to leave the subv_writers counter of the root, used for synchronization between buffered nocow writers and snapshotting. This happens in an exceptional case like the following: 1) We fail to allocate data space for the write, since there's not enough available data space nor enough unallocated space for allocating a new data block group; 2) Because of that failure, we try to go to NOCOW mode, which succeeds and therefore we set the local variable 'only_release_metadata' to true and set the root's sub_writers counter to 1 through the call to btrfs_start_write_no_snapshotting() made by check_can_nocow(); 3) The call to btrfs_copy_from_user() returns zero, which is very unlikely to happen but not impossible; 4) No pages are copied because btrfs_copy_from_user() returned zero; 5) We call btrfs_end_write_no_snapshotting() which decrements the root's subv_writers counter to 0; 6) We don't set 'only_release_metadata' back to 'false' because we do it only if 'copied', the value returned by btrfs_copy_from_user(), is greater than zero; 7) On the next iteration of the while loop, which processes the same page range, we are now able to allocate data space for the write (we got enough data space released in the meanwhile); 8) After this if we fail at btrfs_delalloc_reserve_metadata(), because now there isn't enough free metadata space, or in some other place further below (prepare_pages(), lock_and_cleanup_extent_if_need(), btrfs_dirty_pages()), we break out of the while loop with 'only_release_metadata' having a value of 'true'; 9) Because 'only_release_metadata' is 'true' we end up decrementing the root's subv_writers counter to -1 (through a call to btrfs_end_write_no_snapshotting()), and we also end up not releasing the data space previously reserved through btrfs_check_data_free_space(). As a consequence the mechanism for synchronizing NOCOW buffered writes with snapshotting gets broken. Fix this by always setting 'only_release_metadata' to false at the start of each iteration. Fixes: 8257b2dc3c1a10 ("Btrfs: introduce btrfs_{start, end}_nocow_write() for each subvolume") Fixes: 7ee9e4405f264e ("Btrfs: check if we can nocow if we don't have data space") Signed-off-by: Filipe Manana Reviewed-by: Josef Bacik --- V2: Moved assignment of false to only_release_metadata to the beginning of loop instead. And another "Fixes:" tag that corresponds to the data space leak, since the other if for counter dropping to -1 bug. fs/btrfs/file.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c index 27e5b269e729..352928b45d2a 100644 --- a/fs/btrfs/file.c +++ b/fs/btrfs/file.c @@ -1636,6 +1636,7 @@ static noinline ssize_t btrfs_buffered_write(struct kiocb *iocb, break; } + only_release_metadata = false; sector_offset = pos & (fs_info->sectorsize - 1); reserve_bytes = round_up(write_bytes + sector_offset, fs_info->sectorsize); @@ -1792,7 +1793,6 @@ static noinline ssize_t btrfs_buffered_write(struct kiocb *iocb, set_extent_bit(&BTRFS_I(inode)->io_tree, lockstart, lockend, EXTENT_NORESERVE, NULL, NULL, GFP_NOFS); - only_release_metadata = false; } btrfs_drop_pages(pages, num_pages);