From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtp.codeaurora.org by pdx-caf-mail.web.codeaurora.org (Dovecot) with LMTP id Syu3IjJPGVsmfAAAmS7hNA ; Thu, 07 Jun 2018 15:31:23 +0000 Received: by smtp.codeaurora.org (Postfix, from userid 1000) id 44C3C60115; Thu, 7 Jun 2018 15:31:23 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on pdx-caf-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.9 required=2.0 tests=BAYES_00,MAILING_LIST_MULTI autolearn=ham autolearn_force=no version=3.4.0 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by smtp.codeaurora.org (Postfix) with ESMTP id 00A89608C8; Thu, 7 Jun 2018 15:31:19 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 smtp.codeaurora.org 00A89608C8 Authentication-Results: pdx-caf-mail.web.codeaurora.org; dmarc=none (p=none dis=none) header.from=decadent.org.uk Authentication-Results: pdx-caf-mail.web.codeaurora.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934572AbeFGPbS (ORCPT + 25 others); Thu, 7 Jun 2018 11:31:18 -0400 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:40974 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S935190AbeFGOyC (ORCPT ); Thu, 7 Jun 2018 10:54:02 -0400 Received: from [148.252.241.226] (helo=deadeye) by shadbolt.decadent.org.uk with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.84_2) (envelope-from ) id 1fQvbG-0005Zi-69; Thu, 07 Jun 2018 15:09:14 +0100 Received: from ben by deadeye with local (Exim 4.91) (envelope-from ) id 1fQvbC-0003FT-Qz; Thu, 07 Jun 2018 15:09:10 +0100 Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit MIME-Version: 1.0 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org CC: akpm@linux-foundation.org, "Jann Horn" , "Kent Overstreet" , "Tejun Heo" , "Linus Torvalds" Date: Thu, 07 Jun 2018 15:05:21 +0100 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) Subject: [PATCH 3.16 357/410] fs/aio: Add explicit RCU grace period when freeing kioctx In-Reply-To: X-SA-Exim-Connect-IP: 148.252.241.226 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.16.57-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Tejun Heo commit a6d7cff472eea87d96899a20fa718d2bab7109f3 upstream. While fixing refcounting, e34ecee2ae79 ("aio: Fix a trinity splat") incorrectly removed explicit RCU grace period before freeing kioctx. The intention seems to be depending on the internal RCU grace periods of percpu_ref; however, percpu_ref uses a different flavor of RCU, sched-RCU. This can lead to kioctx being freed while RCU read protected dereferences are still in progress. Fix it by updating free_ioctx() to go through call_rcu() explicitly. v2: Comment added to explain double bouncing. Signed-off-by: Tejun Heo Reported-by: Jann Horn Fixes: e34ecee2ae79 ("aio: Fix a trinity splat") Cc: Kent Overstreet Cc: Linus Torvalds Signed-off-by: Ben Hutchings --- fs/aio.c | 23 +++++++++++++++++++---- 1 file changed, 19 insertions(+), 4 deletions(-) --- a/fs/aio.c +++ b/fs/aio.c @@ -115,7 +115,8 @@ struct kioctx { struct page **ring_pages; long nr_pages; - struct work_struct free_work; + struct rcu_head free_rcu; + struct work_struct free_work; /* see free_ioctx() */ /* * signals when all in-flight requests are done @@ -512,6 +513,12 @@ static int kiocb_cancel(struct kiocb *ki return cancel(kiocb); } +/* + * free_ioctx() should be RCU delayed to synchronize against the RCU + * protected lookup_ioctx() and also needs process context to call + * aio_free_ring(), so the double bouncing through kioctx->free_rcu and + * ->free_work. + */ static void free_ioctx(struct work_struct *work) { struct kioctx *ctx = container_of(work, struct kioctx, free_work); @@ -523,6 +530,14 @@ static void free_ioctx(struct work_struc kmem_cache_free(kioctx_cachep, ctx); } +static void free_ioctx_rcufn(struct rcu_head *head) +{ + struct kioctx *ctx = container_of(head, struct kioctx, free_rcu); + + INIT_WORK(&ctx->free_work, free_ioctx); + schedule_work(&ctx->free_work); +} + static void free_ioctx_reqs(struct percpu_ref *ref) { struct kioctx *ctx = container_of(ref, struct kioctx, reqs); @@ -531,8 +546,8 @@ static void free_ioctx_reqs(struct percp if (ctx->rq_wait && atomic_dec_and_test(&ctx->rq_wait->count)) complete(&ctx->rq_wait->comp); - INIT_WORK(&ctx->free_work, free_ioctx); - schedule_work(&ctx->free_work); + /* Synchronize against RCU protected table->table[] dereferences */ + call_rcu(&ctx->free_rcu, free_ioctx_rcufn); } /* @@ -754,7 +769,7 @@ static int kill_ioctx(struct mm_struct * table->table[ctx->id] = NULL; spin_unlock(&mm->ioctx_lock); - /* percpu_ref_kill() will do the necessary call_rcu() */ + /* free_ioctx_reqs() will do the necessary RCU synchronization */ wake_up_all(&ctx->wait); /*