From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-10.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 05307C433DF for ; Fri, 3 Jul 2020 07:06:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E2DD2208FE for ; Fri, 3 Jul 2020 07:06:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726107AbgGCHF7 (ORCPT ); Fri, 3 Jul 2020 03:05:59 -0400 Received: from mx2.suse.de ([195.135.220.15]:37452 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725764AbgGCHF6 (ORCPT ); Fri, 3 Jul 2020 03:05:58 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id BFCAAAC67; Fri, 3 Jul 2020 07:05:54 +0000 (UTC) From: Qu Wenruo To: linux-btrfs@vger.kernel.org Cc: Marcos Paulo de Souza Subject: [PATCH] btrfs: discard: reduce the block group ref when grabbing from unused block group list Date: Fri, 3 Jul 2020 15:05:50 +0800 Message-Id: <20200703070550.39299-1-wqu@suse.com> X-Mailer: git-send-email 2.27.0 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org [BUG] The following small test script can trigger ASSERT() at unmount time: mkfs.btrfs -f $dev mount $dev $mnt mount -o remount,discard=async $mnt umount $mnt The call trace: assertion failed: atomic_read(&block_group->count) == 1, in fs/btrfs/block-group.c:3431 ------------[ cut here ]------------ kernel BUG at fs/btrfs/ctree.h:3204! invalid opcode: 0000 [#1] PREEMPT SMP NOPTI CPU: 4 PID: 10389 Comm: umount Tainted: G O 5.8.0-rc3-custom+ #68 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015 Call Trace: btrfs_free_block_groups.cold+0x22/0x55 [btrfs] close_ctree+0x2cb/0x323 [btrfs] btrfs_put_super+0x15/0x17 [btrfs] generic_shutdown_super+0x72/0x110 kill_anon_super+0x18/0x30 btrfs_kill_super+0x17/0x30 [btrfs] deactivate_locked_super+0x3b/0xa0 deactivate_super+0x40/0x50 cleanup_mnt+0x135/0x190 __cleanup_mnt+0x12/0x20 task_work_run+0x64/0xb0 __prepare_exit_to_usermode+0x1bc/0x1c0 __syscall_return_slowpath+0x47/0x230 do_syscall_64+0x64/0xb0 entry_SYSCALL_64_after_hwframe+0x44/0xa9 The code: ASSERT(atomic_read(&block_group->count) == 1); btrfs_put_block_group(block_group); [CAUSE] Obviously it's some btrfs_get_block_group() call doesn't get its put call. The offending btrfs_get_block_group() happens here: void btrfs_mark_bg_unused(struct btrfs_block_group *bg) { if (list_empty(&bg->bg_list)) { btrfs_get_block_group(bg); list_add_tail(&bg->bg_list, &fs_info->unused_bgs); } } So every call sites removing the block group from unused_bgs list should reduce the ref count of that block group. However for async discard, it didn't follow the call convention: void btrfs_discard_punt_unused_bgs_list(struct btrfs_fs_info *fs_info) { list_for_each_entry_safe(block_group, next, &fs_info->unused_bgs, bg_list) { list_del_init(&block_group->bg_list); btrfs_discard_queue_work(&fs_info->discard_ctl, block_group); } } And in btrfs_discard_queue_work(), it doesn't call btrfs_put_block_group() either. [FIX] Fix the problem by reducing the reference count when we grab the block group from unused_bgs list. Reported-by: Marcos Paulo de Souza Fixes: 6e80d4f8c422 ("btrfs: handle empty block_group removal for async discard") Signed-off-by: Qu Wenruo --- fs/btrfs/discard.c | 1 + 1 file changed, 1 insertion(+) diff --git a/fs/btrfs/discard.c b/fs/btrfs/discard.c index 5615320fa659..741c7e19c32f 100644 --- a/fs/btrfs/discard.c +++ b/fs/btrfs/discard.c @@ -619,6 +619,7 @@ void btrfs_discard_punt_unused_bgs_list(struct btrfs_fs_info *fs_info) list_for_each_entry_safe(block_group, next, &fs_info->unused_bgs, bg_list) { list_del_init(&block_group->bg_list); + btrfs_put_block_group(block_group); btrfs_discard_queue_work(&fs_info->discard_ctl, block_group); } spin_unlock(&fs_info->unused_bgs_lock); -- 2.27.0