From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from cn.fujitsu.com ([59.151.112.132]:4290 "EHLO heian.cn.fujitsu.com" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S1750817AbaGCLFk (ORCPT ); Thu, 3 Jul 2014 07:05:40 -0400 Message-ID: <53B53973.9070302@cn.fujitsu.com> Date: Thu, 3 Jul 2014 19:07:31 +0800 From: Miao Xie Reply-To: MIME-Version: 1.0 To: Satoru Takeuchi , Filipe David Borba Manana , Subject: Re: [PATCH v2] Btrfs: fix crash when starting transaction References: <1403524739-28436-1-git-send-email-fdmanana@gmail.com> <1403628418-28442-1-git-send-email-fdmanana@gmail.com> <53B514BB.40601@cn.fujitsu.com> <53B53132.4040601@jp.fujitsu.com> In-Reply-To: <53B53132.4040601@jp.fujitsu.com> Content-Type: text/plain; charset="UTF-8" Sender: linux-btrfs-owner@vger.kernel.org List-ID: On Thu, 3 Jul 2014 19:32:18 +0900, Satoru Takeuchi wrote: > (2014/07/03 17:30), Miao Xie wrote: >> On Tue, 24 Jun 2014 17:46:58 +0100, Filipe David Borba Manana wrote: >>> Often when starting a transaction we commit the currently running transaction, >>> which can end up writing block group caches when the current process has its >>> journal_info set to NULL (and not to a transaction). This makes our assertion >>> at btrfs_check_data_free_space() (current_journal != NULL) fail, resulting >>> in a crash/hang. Therefore fix it by setting journal_info. >>> >>> Two different traces of this issue follow below. >>> >>> 1) >>> >>> [51502.241936] BTRFS: assertion failed: current->journal_info, file: fs/btrfs/extent-tree.c, line: 3670 >>> [51502.242213] ------------[ cut here ]------------ >>> [51502.242493] kernel BUG at fs/btrfs/ctree.h:3964! >>> [51502.242669] invalid opcode: 0000 [#1] SMP DEBUG_PAGEALLOC >>> (...) >>> [51502.244010] Call Trace: >>> [51502.244010] [] btrfs_check_data_free_space+0x395/0x3a0 [btrfs] >>> [51502.244010] [] btrfs_write_dirty_block_groups+0x4ac/0x640 [btrfs] >>> [51502.244010] [] commit_cowonly_roots+0x164/0x226 [btrfs] >>> [51502.244010] [] btrfs_commit_transaction+0x4ed/0xab0 [btrfs] >>> [51502.244010] [] ? _raw_spin_unlock+0x2b/0x40 >>> [51502.244010] [] start_transaction+0x459/0x620 [btrfs] >>> [51502.244010] [] btrfs_start_transaction+0x1b/0x20 [btrfs] >>> [51502.244010] [] __unlink_start_trans+0x31/0xe0 [btrfs] >>> [51502.244010] [] btrfs_unlink+0x37/0xc0 [btrfs] >>> [51502.244010] [] ? do_unlinkat+0x114/0x2a0 >>> [51502.244010] [] vfs_unlink+0xcc/0x150 >>> [51502.244010] [] do_unlinkat+0x260/0x2a0 >>> [51502.244010] [] ? filp_close+0x64/0x90 >>> [51502.244010] [] ? trace_hardirqs_on_caller+0x16/0x1e0 >>> [51502.244010] [] ? trace_hardirqs_on_thunk+0x3a/0x3f >>> [51502.244010] [] SyS_unlinkat+0x1b/0x40 >>> [51502.244010] [] system_call_fastpath+0x16/0x1b >>> [51502.244010] Code: 0b 55 48 89 e5 0f 0b 55 48 89 e5 0f 0b 55 89 f1 48 c7 c2 71 13 36 a0 48 89 fe 31 c0 48 c7 c7 b8 43 36 a0 48 89 e5 e8 5d b0 32 e1 <0f> 0b 0f 1f 44 00 00 55 b9 11 00 00 00 48 89 e5 41 55 49 89 f5 >>> [51502.244010] RIP [] assfail.constprop.88+0x1e/0x20 [btrfs] >>> >>> 2) >>> >>> [25405.097230] BTRFS: assertion failed: current->journal_info, file: fs/btrfs/extent-tree.c, line: 3670 >>> [25405.097488] ------------[ cut here ]------------ >>> [25405.097767] kernel BUG at fs/btrfs/ctree.h:3964! >>> [25405.097940] invalid opcode: 0000 [#1] SMP DEBUG_PAGEALLOC >>> (...) >>> [25405.100008] Call Trace: >>> [25405.100008] [] btrfs_check_data_free_space+0x395/0x3a0 [btrfs] >>> [25405.100008] [] btrfs_write_dirty_block_groups+0x4ac/0x640 [btrfs] >>> [25405.100008] [] commit_cowonly_roots+0x164/0x226 [btrfs] >>> [25405.100008] [] btrfs_commit_transaction+0x4ed/0xab0 [btrfs] >>> [25405.100008] [] ? bit_waitqueue+0xc0/0xc0 >>> [25405.100008] [] start_transaction+0x459/0x620 [btrfs] >>> [25405.100008] [] btrfs_start_transaction+0x1b/0x20 [btrfs] >>> [25405.100008] [] btrfs_create+0x47/0x210 [btrfs] >>> [25405.100008] [] ? btrfs_permission+0x3c/0x80 [btrfs] >>> [25405.100008] [] vfs_create+0x9b/0x130 >>> [25405.100008] [] do_last+0x849/0xe20 >>> [25405.100008] [] ? link_path_walk+0x79/0x820 >>> [25405.100008] [] path_openat+0xc5/0x690 >>> [25405.100008] [] ? trace_hardirqs_on+0xd/0x10 >>> [25405.100008] [] ? __alloc_fd+0x32/0x1d0 >>> [25405.100008] [] do_filp_open+0x43/0xa0 >>> [25405.100008] [] ? __alloc_fd+0x151/0x1d0 >>> [25405.100008] [] do_sys_open+0x13c/0x230 >>> [25405.100008] [] ? trace_hardirqs_on_caller+0x16/0x1e0 >>> [25405.100008] [] SyS_open+0x22/0x30 >>> [25405.100008] [] system_call_fastpath+0x16/0x1b >>> [25405.100008] Code: 0b 55 48 89 e5 0f 0b 55 48 89 e5 0f 0b 55 89 f1 48 c7 c2 51 13 36 a0 48 89 fe 31 c0 48 c7 c7 d0 43 36 a0 48 89 e5 e8 6d b5 32 e1 <0f> 0b 0f 1f 44 00 00 55 b9 11 00 00 00 48 89 e5 41 55 49 89 f5 >>> [25405.100008] RIP [] assfail.constprop.88+0x1e/0x20 [btrfs] >>> >>> Signed-off-by: Filipe David Borba Manana >>> --- >>> >>> V2: Removed test for current->journal_info == NULL. At this point it's >>> always expected to be NULL. >> >> Reviewed-by: Miao Xie > > Let me clarify my understanding since I'm not good at the transaction code. > > * What is the route cause? > > When start_transaction() is called with current->journal_transaction == NULL, > we hit BUG() in the following path. > > start_transaction > -> btrfs_commit_transaction > -> commit_cowonly_roots > -> update_cowonly_root > -> btrfs_write_dirty_block_groups > -> cache_save_setup > -> btrfs_check_data_free_space > ASSERT(current->journal_info) # it fails and hits BUG()! Yes, you are right. > > * Why NULL check is not necessary? > > fs/btrfs/transaction.c: > =============================================================================== > start_transaction(...) { > if (current->journal_info && > current->journal_info != (void *)BTRFS_SEND_TRANS_STUB) { > ... > goto got_it; > =============================================================================== > To begin with, if current->journal_info == BTRFS_SEND_TRANS_STUB, > start_transaction() should not be called. Filipe's another patch > ([PATCH] Btrfs: assert send doesn't attempt to start) is to change > the second condition to ASSERT(). > > If current->journal_transaction is a "real" transaction, the > above-mentioned code path is skipped because of "goto got_it". > > Is my understanding correct? Yes, you are right. And only JOIN/JOIN_NOLOCK can join the current transaction handle, the others is forbidden. Thanks Miao > > BTW, Filipe, although I've tried to reproduce this problem for two days > by running xfstests loop, it didn't happen yet with my environment ;-( > So all I can do seems to be code review. > > Thanks, > Satoru > >>> >>> fs/btrfs/transaction.c | 1 + >>> 1 file changed, 1 insertion(+) >>> >>> diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c >>> index ac984a3..614eac3 100644 >>> --- a/fs/btrfs/transaction.c >>> +++ b/fs/btrfs/transaction.c >>> @@ -491,6 +491,7 @@ again: >>> smp_mb(); >>> if (cur_trans->state >= TRANS_STATE_BLOCKED && >>> may_wait_transaction(root, type)) { >>> + current->journal_info = h; >>> btrfs_commit_transaction(h, root); >>> goto again; >>> } >>> >> >> -- >> To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in >> the body of a message to majordomo@vger.kernel.org >> More majordomo info at http://vger.kernel.org/majordomo-info.html >> > > . >