From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lj1-f176.google.com (mail-lj1-f176.google.com [209.85.208.176]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by dev.tarantool.org (Postfix) with ESMTPS id 201A646970E for ; Tue, 28 Jan 2020 22:23:28 +0300 (MSK) Received: by mail-lj1-f176.google.com with SMTP id a13so15877615ljm.10 for ; Tue, 28 Jan 2020 11:23:28 -0800 (PST) From: Cyrill Gorcunov Date: Tue, 28 Jan 2020 22:22:47 +0300 Message-Id: <20200128192249.10023-4-gorcunov@gmail.com> In-Reply-To: <20200128192249.10023-1-gorcunov@gmail.com> References: <20200128192249.10023-1-gorcunov@gmail.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Subject: [Tarantool-patches] [PATCH v7 3/5] box/applier: fix nil dereference in applier rollback List-Id: Tarantool development patches List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: tml Currently when transaction rollback happens we just drop an existing error setting ClientError to the replicaset.applier.diag. This action leaves current fiber with diag=nil, which in turn leads to sigsegv once diag_raise() called right after applier_apply_tx(): | applier_f | try { | applier_subscribe | applier_apply_tx | // error happens | txn_rollback | diag_set(ClientError, ER_WAL_IO) | diag_move(&fiber()->diag, &replicaset.applier.diag) | // fiber->diag = nil | applier_on_rollback | diag_add_error(&applier->diag, diag_last_error(&replicaset.applier.diag) | fiber_cancel(applier->reader); | diag_raise() -> NULL dereference | } catch { ... } The applier_f works in try/catch cycle and handles errors depending on what exactly happened during transaction application. It might reconnect appliers in some cases, the applier is simply cancelled and reaped out in others. The problem is that the shared replicaset.applier.diag is handled on FiberIsCancelled exception only (while it is set inside transaction rollback action) and we never trigger this specific exception. But even if we would the former error which has been causing the applier abort is vanished by ClientError which is too general. Thus: - on transaction rollback save the origin error which caused the transaction abort to the replicaset.applier.diag; - there are cases (such as xlog error injection) where diag is explicitly clear on error path, for this sake we setup ClientError instead; - trigger FiberIsCancelled exception which will log the problem and zap the applier; - put fixme mark into the code: we need to figure out if underlierd error is really critical one maybe we could retry the applier iteration instead. Part-of #4730 Signed-off-by: Cyrill Gorcunov --- src/box/applier.cc | 43 +++++++++++++++++++++++++++++++++++++++---- 1 file changed, 39 insertions(+), 4 deletions(-) diff --git a/src/box/applier.cc b/src/box/applier.cc index 2ed5125d0..967dc91de 100644 --- a/src/box/applier.cc +++ b/src/box/applier.cc @@ -692,9 +692,31 @@ static int applier_txn_rollback_cb(struct trigger *trigger, void *event) { (void) trigger; - /* Setup shared applier diagnostic area. */ - diag_set(ClientError, ER_WAL_IO); - diag_move(&fiber()->diag, &replicaset.applier.diag); + + /* + * We must not loose the origin error, instead + * lets keep it in replicaset diag instance. + * + * FIXME: We need to revisit this code and + * figure out if we can reconnect and retry + * the prelication process instead of cancelling + * applier with FiberIsCancelled. + */ + struct error *e = diag_last_error(diag_get()); + if (!e) { + /* + * If information is already lost + * (say xlog cleared diag instance) + * setup general ClientError, seriously + * we need to unweave this mess, if error + * happened it must never been cleared + * until error handling in rollback. + */ + diag_set(ClientError, ER_WAL_IO); + e = diag_last_error(diag_get()); + } + diag_add_error(&replicaset.applier.diag, e); + /* Broadcast the rollback event across all appliers. */ trigger_run(&replicaset.applier.on_rollback, event); /* Rollback applier vclock to the committed one. */ @@ -849,8 +871,20 @@ applier_on_rollback(struct trigger *trigger, void *event) diag_add_error(&applier->diag, diag_last_error(&replicaset.applier.diag)); } - /* Stop the applier fiber. */ + + /* + * Something really bad happened, we can't proceed + * thus stop the applier and throw FiberIsCancelled + * exception which will be catched by the caller + * and the fiber gracefully finish. + * + * FIXME: Need to make sure that this is a really + * final error where we can't longer proceed and should + * zap the applier, probably we could reconnect and + * retry instead? + */ fiber_cancel(applier->reader); + diag_set(FiberIsCancelled); return 0; } @@ -1098,6 +1132,7 @@ applier_f(va_list ap) } catch (FiberIsCancelled *e) { if (!diag_is_empty(&applier->diag)) { diag_move(&applier->diag, &fiber()->diag); + diag_log(); applier_disconnect(applier, APPLIER_STOPPED); break; } -- 2.20.1