From owner-svn-src-stable@freebsd.org Thu Mar 16 01:41:37 2017 Return-Path: Delivered-To: svn-src-stable@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 87E34D0C0AD; Thu, 16 Mar 2017 01:41:37 +0000 (UTC) (envelope-from badger@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 618701D5F; Thu, 16 Mar 2017 01:41:37 +0000 (UTC) (envelope-from badger@FreeBSD.org) Received: from repo.freebsd.org ([127.0.1.37]) by repo.freebsd.org (8.15.2/8.15.2) with ESMTP id v2G1fawC062421; Thu, 16 Mar 2017 01:41:36 GMT (envelope-from badger@FreeBSD.org) Received: (from badger@localhost) by repo.freebsd.org (8.15.2/8.15.2/Submit) id v2G1fahX062420; Thu, 16 Mar 2017 01:41:36 GMT (envelope-from badger@FreeBSD.org) Message-Id: <201703160141.v2G1fahX062420@repo.freebsd.org> X-Authentication-Warning: repo.freebsd.org: badger set sender to badger@FreeBSD.org using -f From: Eric Badger Date: Thu, 16 Mar 2017 01:41:36 +0000 (UTC) To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-stable@freebsd.org, svn-src-stable-10@freebsd.org Subject: svn commit: r315345 - stable/10/sys/kern X-SVN-Group: stable-10 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-BeenThere: svn-src-stable@freebsd.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: SVN commit messages for all the -stable branches of the src tree List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 16 Mar 2017 01:41:37 -0000 Author: badger Date: Thu Mar 16 01:41:36 2017 New Revision: 315345 URL: https://svnweb.freebsd.org/changeset/base/315345 Log: MFC r313733: sleepq_catch_signals: do thread suspension before signal check Since locks are dropped when a thread suspends, it's possible for another thread to deliver a signal to the suspended thread. If the thread awakens from suspension without checking for signals, it may go to sleep despite having a pending signal that should wake it up. Therefore the suspension check is done first, so any signals sent while suspended will be caught in the subsequent signal check. Sponsored by: Dell EMC Modified: stable/10/sys/kern/subr_sleepqueue.c Directory Properties: stable/10/ (props changed) Modified: stable/10/sys/kern/subr_sleepqueue.c ============================================================================== --- stable/10/sys/kern/subr_sleepqueue.c Thu Mar 16 01:38:07 2017 (r315344) +++ stable/10/sys/kern/subr_sleepqueue.c Thu Mar 16 01:41:36 2017 (r315345) @@ -411,6 +411,7 @@ sleepq_catch_signals(void *wchan, int pr struct sigacts *ps; int sig, ret; + ret = 0; td = curthread; p = curproc; sc = SC_LOOKUP(wchan); @@ -424,44 +425,51 @@ sleepq_catch_signals(void *wchan, int pr } /* - * See if there are any pending signals for this thread. If not - * we can switch immediately. Otherwise do the signal processing - * directly. + * See if there are any pending signals or suspension requests for this + * thread. If not, we can switch immediately. */ thread_lock(td); - if ((td->td_flags & (TDF_NEEDSIGCHK | TDF_NEEDSUSPCHK)) == 0) { - sleepq_switch(wchan, pri); - return (0); - } - thread_unlock(td); - mtx_unlock_spin(&sc->sc_lock); - CTR3(KTR_PROC, "sleepq catching signals: thread %p (pid %ld, %s)", - (void *)td, (long)p->p_pid, td->td_name); - PROC_LOCK(p); - ps = p->p_sigacts; - mtx_lock(&ps->ps_mtx); - sig = cursig(td); - if (sig == 0) { - mtx_unlock(&ps->ps_mtx); - ret = thread_suspend_check(1); - MPASS(ret == 0 || ret == EINTR || ret == ERESTART); - } else { - if (SIGISMEMBER(ps->ps_sigintr, sig)) - ret = EINTR; - else - ret = ERESTART; - mtx_unlock(&ps->ps_mtx); + if ((td->td_flags & (TDF_NEEDSIGCHK | TDF_NEEDSUSPCHK)) != 0) { + thread_unlock(td); + mtx_unlock_spin(&sc->sc_lock); + CTR3(KTR_PROC, "sleepq catching signals: thread %p (pid %ld, %s)", + (void *)td, (long)p->p_pid, td->td_name); + PROC_LOCK(p); + /* + * Check for suspension first. Checking for signals and then + * suspending could result in a missed signal, since a signal + * can be delivered while this thread is suspended. + */ + if ((td->td_flags & TDF_NEEDSUSPCHK) != 0) { + ret = thread_suspend_check(1); + MPASS(ret == 0 || ret == EINTR || ret == ERESTART); + if (ret != 0) { + PROC_UNLOCK(p); + mtx_lock_spin(&sc->sc_lock); + thread_lock(td); + goto out; + } + } + if ((td->td_flags & TDF_NEEDSIGCHK) != 0) { + ps = p->p_sigacts; + mtx_lock(&ps->ps_mtx); + sig = cursig(td); + if (sig != 0) + ret = SIGISMEMBER(ps->ps_sigintr, sig) ? + EINTR : ERESTART; + mtx_unlock(&ps->ps_mtx); + } + /* + * Lock the per-process spinlock prior to dropping the PROC_LOCK + * to avoid a signal delivery race. PROC_LOCK, PROC_SLOCK, and + * thread_lock() are currently held in tdsendsignal(). + */ + PROC_SLOCK(p); + mtx_lock_spin(&sc->sc_lock); + PROC_UNLOCK(p); + thread_lock(td); + PROC_SUNLOCK(p); } - /* - * Lock the per-process spinlock prior to dropping the PROC_LOCK - * to avoid a signal delivery race. PROC_LOCK, PROC_SLOCK, and - * thread_lock() are currently held in tdsendsignal(). - */ - PROC_SLOCK(p); - mtx_lock_spin(&sc->sc_lock); - PROC_UNLOCK(p); - thread_lock(td); - PROC_SUNLOCK(p); if (ret == 0) { sleepq_switch(wchan, pri); return (0);