From owner-svn-src-head@freebsd.org Mon Aug 21 11:51:41 2017 Return-Path: Delivered-To: svn-src-head@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id 5C656DD53F1; Mon, 21 Aug 2017 11:51:41 +0000 (UTC) (envelope-from hselasky@FreeBSD.org) Received: from repo.freebsd.org (repo.freebsd.org [IPv6:2610:1c1:1:6068::e6a:0]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id 290BA6C1A3; Mon, 21 Aug 2017 11:51:41 +0000 (UTC) (envelope-from hselasky@FreeBSD.org) Received: from repo.freebsd.org ([127.0.1.37]) by repo.freebsd.org (8.15.2/8.15.2) with ESMTP id v7LBpeYI077808; Mon, 21 Aug 2017 11:51:40 GMT (envelope-from hselasky@FreeBSD.org) Received: (from hselasky@localhost) by repo.freebsd.org (8.15.2/8.15.2/Submit) id v7LBpeH2077807; Mon, 21 Aug 2017 11:51:40 GMT (envelope-from hselasky@FreeBSD.org) Message-Id: <201708211151.v7LBpeH2077807@repo.freebsd.org> X-Authentication-Warning: repo.freebsd.org: hselasky set sender to hselasky@FreeBSD.org using -f From: Hans Petter Selasky Date: Mon, 21 Aug 2017 11:51:40 +0000 (UTC) To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r322746 - head/sys/compat/linuxkpi/common/src X-SVN-Group: head X-SVN-Commit-Author: hselasky X-SVN-Commit-Paths: head/sys/compat/linuxkpi/common/src X-SVN-Commit-Revision: 322746 X-SVN-Commit-Repository: base MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-BeenThere: svn-src-head@freebsd.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: SVN commit messages for the src tree for head/-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 21 Aug 2017 11:51:41 -0000 Author: hselasky Date: Mon Aug 21 11:51:40 2017 New Revision: 322746 URL: https://svnweb.freebsd.org/changeset/base/322746 Log: Fix for deadlock situation in the LinuxKPI's RCU synchronize API. Deadlock condition: The return value of TDQ_LOCKPTR(td) is the same for two threads. 1) The first thread signals a wakeup while keeping the rcu_read_lock(). This invokes sched_add() which in turn will try to lock TDQ_LOCK(). 2) The second thread is calling synchronize_rcu() calling mi_switch() over and over again trying to yield(). This prevents the first thread from running and releasing the RCU reader lock. Solution: Release the thread lock while yielding to allow other threads to acquire the lock pointed to by TDQ_LOCKPTR(td). Found by: KrishnamRaju ErapaRaju MFC after: 1 week Sponsored by: Mellanox Technologies Modified: head/sys/compat/linuxkpi/common/src/linux_rcu.c Modified: head/sys/compat/linuxkpi/common/src/linux_rcu.c ============================================================================== --- head/sys/compat/linuxkpi/common/src/linux_rcu.c Mon Aug 21 10:26:11 2017 (r322745) +++ head/sys/compat/linuxkpi/common/src/linux_rcu.c Mon Aug 21 11:51:40 2017 (r322746) @@ -258,6 +258,15 @@ linux_synchronize_rcu_cb(ck_epoch_t *epoch __unused, c sched_prio(td, prio); /* task switch */ mi_switch(SW_VOL | SWT_RELINQUISH, NULL); + + /* + * Release the thread lock while yielding to + * allow other threads to acquire the lock + * pointed to by TDQ_LOCKPTR(td). Else a + * deadlock like situation might happen. + */ + thread_unlock(td); + thread_lock(td); } } else { /*