From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-la0-f49.google.com ([209.85.215.49]:51736 "EHLO mail-la0-f49.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751163AbaFMJJs (ORCPT ); Fri, 13 Jun 2014 05:09:48 -0400 Received: by mail-la0-f49.google.com with SMTP id gf5so715293lab.8 for ; Fri, 13 Jun 2014 02:09:46 -0700 (PDT) MIME-Version: 1.0 Reply-To: fdmanana@gmail.com In-Reply-To: <1402424236-13459-1-git-send-email-fdmanana@gmail.com> References: <1402423961-12169-1-git-send-email-fdmanana@gmail.com> <1402424236-13459-1-git-send-email-fdmanana@gmail.com> Date: Fri, 13 Jun 2014 10:09:46 +0100 Message-ID: Subject: Re: [PATCH v2] Btrfs: fix RCU correctness warning when running sanity tests From: Filipe David Manana To: "linux-btrfs@vger.kernel.org" Cc: Filipe David Borba Manana , Chris Mason Content-Type: text/plain; charset=UTF-8 Sender: linux-btrfs-owner@vger.kernel.org List-ID: On Tue, Jun 10, 2014 at 7:17 PM, Filipe David Borba Manana wrote: > When CONFIG_PROVE_RCU=y and CONFIG_PROVE_RCU_REPEATEDLY=y, the > following was dumped in dmesg: > > [ 3197.218064] =============================== > [ 3197.218064] [ INFO: suspicious RCU usage. ] > [ 3197.218066] 3.15.0-rc8-fdm-btrfs-next-33+ #4 Not tainted > [ 3197.218067] ------------------------------- > [ 3197.218068] include/linux/radix-tree.h:196 suspicious rcu_dereference_check() usage! > [ 3197.218068] > [ 3197.218068] other info that might help us debug this: > [ 3197.218068] > [ 3197.218070] > [ 3197.218070] rcu_scheduler_active = 1, debug_locks = 1 > [ 3197.218071] 1 lock held by modprobe/12024: > [ 3197.218072] #0: (&(&fs_info->buffer_lock)->rlock){+.+...}, at: [] btrfs_free_dummy_root+0x5a/0x1d0 [btrfs] > [ 3197.218093] > [ 3197.218093] stack backtrace: > [ 3197.218095] CPU: 3 PID: 12024 Comm: modprobe Not tainted 3.15.0-rc8-fdm-btrfs-next-33+ #4 > [ 3197.218096] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011 > [ 3197.218097] 0000000000000001 ffff8800af18fc18 ffffffff81685c5a 000000000000feb0 > [ 3197.218099] ffff8800cf6ccb40 ffff8800af18fc48 ffffffff810a6316 ffff8801d955f640 > [ 3197.218101] ffff8800d719e328 ffff8800d719e370 ffff8800d719c000 ffff8800af18fcb8 > [ 3197.218102] Call Trace: > [ 3197.218105] [] dump_stack+0x4e/0x68 > [ 3197.218108] [] lockdep_rcu_suspicious+0xe6/0x130 > [ 3197.218119] [] btrfs_free_dummy_root+0x188/0x1d0 [btrfs] > [ 3197.218129] [] btrfs_test_qgroups+0xea/0x1bb [btrfs] > [ 3197.218137] [] ? ftrace_define_fields_btrfs_space_reservation+0xfd/0xfd [btrfs] > [ 3197.218144] [] ? ftrace_define_fields_btrfs_space_reservation+0xfd/0xfd [btrfs] > [ 3197.218151] [] init_btrfs_fs+0xe5/0x184 [btrfs] > [ 3197.218154] [] do_one_initcall+0x102/0x150 > [ 3197.218157] [] ? set_memory_nx+0x43/0x50 > [ 3197.218160] [] ? set_section_ro_nx+0x6d/0x74 > [ 3197.218162] [] load_module+0x1cdc/0x2630 > [ 3197.218164] [] ? show_initstate+0x60/0x60 > [ 3197.218166] [] SyS_finit_module+0x8e/0x90 > [ 3197.218168] [] system_call_fastpath+0x16/0x1b > > Signed-off-by: Filipe David Borba Manana Chris, Please drop this patch from your integration branch. Sasha fixed this too but in a simpler way: https://patchwork.kernel.org/patch/4337091/ (In fact both patches applied probably trigger another warning the rcu usage correctness checker) Thanks > --- > > V2: Added missing rcu read unlock if a retry is needed. > > fs/btrfs/tests/btrfs-tests.c | 12 +++++++----- > 1 file changed, 7 insertions(+), 5 deletions(-) > > diff --git a/fs/btrfs/tests/btrfs-tests.c b/fs/btrfs/tests/btrfs-tests.c > index a5dcacb..bdb1f05 100644 > --- a/fs/btrfs/tests/btrfs-tests.c > +++ b/fs/btrfs/tests/btrfs-tests.c > @@ -130,8 +130,8 @@ static void btrfs_free_dummy_fs_info(struct btrfs_fs_info *fs_info) > struct radix_tree_iter iter; > void **slot; > > - spin_lock(&fs_info->buffer_lock); > restart: > + rcu_read_lock(); > radix_tree_for_each_slot(slot, &fs_info->buffer_radix, &iter, 0) { > struct extent_buffer *eb; > > @@ -140,15 +140,17 @@ restart: > continue; > /* Shouldn't happen but that kind of thinking creates CVE's */ > if (radix_tree_exception(eb)) { > - if (radix_tree_deref_retry(eb)) > + if (radix_tree_deref_retry(eb)) { > + rcu_read_unlock(); > goto restart; > + } > continue; > } > - spin_unlock(&fs_info->buffer_lock); > + rcu_read_unlock(); > free_extent_buffer_stale(eb); > - spin_lock(&fs_info->buffer_lock); > + goto restart; > } > - spin_unlock(&fs_info->buffer_lock); > + rcu_read_unlock(); > > btrfs_free_qgroup_config(fs_info); > btrfs_free_fs_roots(fs_info); > -- > 1.9.1 > -- Filipe David Manana, "Reasonable men adapt themselves to the world. Unreasonable men adapt the world to themselves. That's why all progress depends on unreasonable men."