From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx2.suse.de ([195.135.220.15]:38407 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752328AbeCNPDV (ORCPT ); Wed, 14 Mar 2018 11:03:21 -0400 Received: from relay1.suse.de (charybdis-ext.suse.de [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id A2333AE0C for ; Wed, 14 Mar 2018 15:03:20 +0000 (UTC) From: Edmund Nadolski To: enadolski@suse.com, linux-btrfs@vger.kernel.org Subject: [PATCH] missing initialization in btrfs_check_shared Date: Wed, 14 Mar 2018 09:03:10 -0600 Message-Id: <20180314150311.20152-1-enadolski@suse.com> Sender: linux-btrfs-owner@vger.kernel.org List-ID: This patch addresses an issue that causes fiemap to falsely report a shared extent. The test case is as follows: # cat do_xfs_io xfs_io -f -d -c "pwrite -b 16k 0 64k" -c "fiemap -v" /media/scratch/file5 sync xfs_io -c "fiemap -v" /media/scratch/file5 which gives the resulting output: # . do_xfs_io wrote 65536/65536 bytes at offset 0 64 KiB, 4 ops; 0.0000 sec (121.359 MiB/sec and 7766.9903 ops/sec) /media/scratch/file5: EXT: FILE-OFFSET BLOCK-RANGE TOTAL FLAGS 0: [0..127]: 24576..24703 128 0x2001 /media/scratch/file5: EXT: FILE-OFFSET BLOCK-RANGE TOTAL FLAGS 0: [0..127]: 24576..24703 128 0x1 This is because btrfs_check_shared calls find_parent_nodes repeatedly in a loop, passing a share_check struct to report the count of shared extent. But btrfs_check_shared does not re-initialize the count value to zero for subsequent calls from the loop, resulting in a false share count value. This is a regressive behavior from 4.13. With proper re-initialization the test result is as follows: # . do_xfs_io wrote 65536/65536 bytes at offset 0 64 KiB, 4 ops; 0.0000 sec (110.035 MiB/sec and 7042.2535 ops/sec) /media/scratch/file5: EXT: FILE-OFFSET BLOCK-RANGE TOTAL FLAGS 0: [0..127]: 24576..24703 128 0x1 /media/scratch/file5: EXT: FILE-OFFSET BLOCK-RANGE TOTAL FLAGS 0: [0..127]: 24576..24703 128 0x1 which corrects the regression. Edmund Nadolski (1): btrfs: add missing initialization in btrfs_check_shared fs/btrfs/backref.c | 1 + 1 file changed, 1 insertion(+) -- 2.10.2