From owner-svn-src-head@freebsd.org Thu Nov 19 18:37:29 2020 Return-Path: Delivered-To: svn-src-head@mailman.nyi.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mailman.nyi.freebsd.org (Postfix) with ESMTP id 530214718CC; Thu, 19 Nov 2020 18:37:29 +0000 (UTC) (envelope-from markj@FreeBSD.org) Received: from mxrelay.nyi.freebsd.org (mxrelay.nyi.freebsd.org [IPv6:2610:1c1:1:606c::19:3]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256 client-signature RSA-PSS (4096 bits) client-digest SHA256) (Client CN "mxrelay.nyi.freebsd.org", Issuer "Let's Encrypt Authority X3" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 4CcT1j1xcjz3Fc5; Thu, 19 Nov 2020 18:37:29 +0000 (UTC) (envelope-from markj@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 mxrelay.nyi.freebsd.org (Postfix) with ESMTPS id 312ECB9C; Thu, 19 Nov 2020 18:37:29 +0000 (UTC) (envelope-from markj@FreeBSD.org) Received: from repo.freebsd.org ([127.0.1.37]) by repo.freebsd.org (8.15.2/8.15.2) with ESMTP id 0AJIbS6e058379; Thu, 19 Nov 2020 18:37:28 GMT (envelope-from markj@FreeBSD.org) Received: (from markj@localhost) by repo.freebsd.org (8.15.2/8.15.2/Submit) id 0AJIbS2E058378; Thu, 19 Nov 2020 18:37:28 GMT (envelope-from markj@FreeBSD.org) Message-Id: <202011191837.0AJIbS2E058378@repo.freebsd.org> X-Authentication-Warning: repo.freebsd.org: markj set sender to markj@FreeBSD.org using -f From: Mark Johnston Date: Thu, 19 Nov 2020 18:37:28 +0000 (UTC) To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r367849 - head/sys/kern X-SVN-Group: head X-SVN-Commit-Author: markj X-SVN-Commit-Paths: head/sys/kern X-SVN-Commit-Revision: 367849 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: 2.1.34 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: Thu, 19 Nov 2020 18:37:29 -0000 Author: markj Date: Thu Nov 19 18:37:28 2020 New Revision: 367849 URL: https://svnweb.freebsd.org/changeset/base/367849 Log: callout(9): Fix a race between CPU migration and callout_drain() Suppose a running callout re-arms itself, and before the callout finishes running another CPU calls callout_drain() and goes to sleep. softclock_call_cc() will wake up the draining thread, which may not run immediately if there is a lot of CPU load. Furthermore, the callout is still in the callout wheel so it can continue to run and re-arm itself. Then, suppose that the callout migrates to another CPU before the draining thread gets a chance to run. The draining thread is in this loop in _callout_stop_safe(): while (cc_exec_curr(cc) == c) { CC_UNLOCK(cc); sleep(); CC_LOCK(cc); } but after the migration, cc points to the wrong CPU's callout state. Then the draining thread goes off and removes the callout from the wheel, but does so using the wrong lock and per-CPU callout state. Fix the problem by doing a re-lookup of the callout CPU after sleeping. Reported by: syzbot+79569cd4d76636b2cc1c@syzkaller.appspotmail.com Reported by: syzbot+1b27e0237aa22d8adffa@syzkaller.appspotmail.com Reported by: syzbot+e21aa5b85a9aff90ef3e@syzkaller.appspotmail.com Reviewed by: emaste, hselasky Tested by: pho MFC after: 1 week Sponsored by: The FreeBSD Foundation Differential Revision: https://reviews.freebsd.org/D27266 Modified: head/sys/kern/kern_timeout.c Modified: head/sys/kern/kern_timeout.c ============================================================================== --- head/sys/kern/kern_timeout.c Thu Nov 19 18:03:40 2020 (r367848) +++ head/sys/kern/kern_timeout.c Thu Nov 19 18:37:28 2020 (r367849) @@ -1145,7 +1145,7 @@ again: * just wait for the current invocation to * finish. */ - while (cc_exec_curr(cc, direct) == c) { + if (cc_exec_curr(cc, direct) == c) { /* * Use direct calls to sleepqueue interface * instead of cv/msleep in order to avoid @@ -1193,7 +1193,7 @@ again: /* Reacquire locks previously released. */ PICKUP_GIANT(); - CC_LOCK(cc); + goto again; } c->c_flags &= ~CALLOUT_ACTIVE; } else if (use_lock &&