From owner-freebsd-bugs@freebsd.org Wed Mar 28 23:21:49 2018 Return-Path: Delivered-To: freebsd-bugs@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id 3297DF53984 for ; Wed, 28 Mar 2018 23:21:49 +0000 (UTC) (envelope-from bugzilla-noreply@freebsd.org) Received: from mxrelay.ysv.freebsd.org (mxrelay.ysv.freebsd.org [IPv6:2001:1900:2254:206a::19:3]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client CN "mxrelay.ysv.freebsd.org", Issuer "Let's Encrypt Authority X3" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id C38CB68DDD for ; Wed, 28 Mar 2018 23:21:48 +0000 (UTC) (envelope-from bugzilla-noreply@freebsd.org) Received: from kenobi.freebsd.org (kenobi.freebsd.org [IPv6:2001:1900:2254:206a::16:76]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by mxrelay.ysv.freebsd.org (Postfix) with ESMTPS id 208701C1E6 for ; Wed, 28 Mar 2018 23:21:48 +0000 (UTC) (envelope-from bugzilla-noreply@freebsd.org) Received: from kenobi.freebsd.org ([127.0.1.118]) by kenobi.freebsd.org (8.15.2/8.15.2) with ESMTP id w2SNLmmC089869 for ; Wed, 28 Mar 2018 23:21:48 GMT (envelope-from bugzilla-noreply@freebsd.org) Received: (from www@localhost) by kenobi.freebsd.org (8.15.2/8.15.2/Submit) id w2SNLmJh089868 for freebsd-bugs@FreeBSD.org; Wed, 28 Mar 2018 23:21:48 GMT (envelope-from bugzilla-noreply@freebsd.org) X-Authentication-Warning: kenobi.freebsd.org: www set sender to bugzilla-noreply@freebsd.org using -f From: bugzilla-noreply@freebsd.org To: freebsd-bugs@FreeBSD.org Subject: [Bug 227041] Kernel cannot fork new process after calling pmc_deatch with pid 0 Date: Wed, 28 Mar 2018 23:21:08 +0000 X-Bugzilla-Reason: AssignedTo X-Bugzilla-Type: changed X-Bugzilla-Watch-Reason: None X-Bugzilla-Product: Base System X-Bugzilla-Component: kern X-Bugzilla-Version: 11.1-RELEASE X-Bugzilla-Keywords: X-Bugzilla-Severity: Affects Some People X-Bugzilla-Who: cem@freebsd.org X-Bugzilla-Status: New X-Bugzilla-Resolution: X-Bugzilla-Priority: --- X-Bugzilla-Assigned-To: freebsd-bugs@FreeBSD.org X-Bugzilla-Flags: X-Bugzilla-Changed-Fields: Message-ID: In-Reply-To: References: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Bugzilla-URL: https://bugs.freebsd.org/bugzilla/ Auto-Submitted: auto-generated MIME-Version: 1.0 X-BeenThere: freebsd-bugs@freebsd.org X-Mailman-Version: 2.1.25 Precedence: list List-Id: Bug reports List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 28 Mar 2018 23:21:49 -0000 https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=3D227041 --- Comment #2 from Conrad Meyer --- The situation described sounds like a deadlock or livelock. If you reprodu= ce it with an INVARIANTS+WITNESS kernel, do you get a LOR warning? Does the pmc-crash program return/complete? Basic investigation: The userspace libpmc functions pmc_detach/pmc_release() translate pretty directly into the (gigantic) kernel syscall pmc_syscall_handler(), PMC_OP_PMCDETACH and PMC_OP_PMCRELEASE. If 0 is passed as pid, the current thread's pid is substituted. pfind() acquires proc lock after pmc sx xlock. The proc lock is dropped and then t= he process is detached via pmc_detach_process(). Are you sure if pmc_release() is required? It doesn't look like it does anything special with locking. I have not investigated deeply. --=20 You are receiving this mail because: You are the assignee for the bug.=