From owner-freebsd-bugs@freebsd.org Wed Feb 10 17:00:09 2016 Return-Path: Delivered-To: freebsd-bugs@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 8D51FAA36DD for ; Wed, 10 Feb 2016 17:00:09 +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 mx1.freebsd.org (Postfix) with ESMTPS id 6442D1D66 for ; Wed, 10 Feb 2016 17:00:09 +0000 (UTC) (envelope-from bugzilla-noreply@freebsd.org) Received: from bugs.freebsd.org ([127.0.1.118]) by kenobi.freebsd.org (8.15.2/8.15.2) with ESMTP id u1AH093R066071 for ; Wed, 10 Feb 2016 17:00:09 GMT (envelope-from bugzilla-noreply@freebsd.org) From: bugzilla-noreply@freebsd.org To: freebsd-bugs@FreeBSD.org Subject: [Bug 207085] pmc assertion failure: pmc %p non-NULL Date: Wed, 10 Feb 2016 17:00:09 +0000 X-Bugzilla-Reason: AssignedTo X-Bugzilla-Type: new X-Bugzilla-Watch-Reason: None X-Bugzilla-Product: Base System X-Bugzilla-Component: kern X-Bugzilla-Version: 10.2-RELEASE X-Bugzilla-Keywords: X-Bugzilla-Severity: Affects Some People X-Bugzilla-Who: joss.upton@yahoo.com 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: bug_id short_desc product version rep_platform op_sys bug_status bug_severity priority component assigned_to reporter cc Message-ID: 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: 2.1.20 Precedence: list List-Id: Bug reports List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 10 Feb 2016 17:00:09 -0000 https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=3D207085 Bug ID: 207085 Summary: pmc assertion failure: pmc %p non-NULL Product: Base System Version: 10.2-RELEASE Hardware: amd64 OS: Any Status: New Severity: Affects Some People Priority: --- Component: kern Assignee: freebsd-bugs@FreeBSD.org Reporter: joss.upton@yahoo.com CC: freebsd-amd64@FreeBSD.org, joss.upton@yahoo.com CC: freebsd-amd64@FreeBSD.org I see these panics with INVARIANTS enabled on 10.2-R on an SMP machine runn= ing many processes using hwpmc in parallel. [core,2376] PHW pmc non-NULL cpuid =3D 1 pmc_process_exit() does the following: sx_xlock(); critical_enter(); free_attached_pmcs... critical_exit(); free_owner_pmcs... sx_unlock(); and the various drivers do *_release_pmc(): ... KASSERT(phw->phw_pmc =3D=3D NULL) ... What I'm seeing is on an SMP machine, from time to time a process which owns PMCs races with a process that has attached PMCs. free_owner_pmcs() calls *_release_pmc() which checks to make sure the per-cpu counter isn't in use. A process with attached pmcs will have freed them with both the pmc_lock and scheduler lock held. But, a process being scheduled onto the pmc can sneak in between the critical_exit() and the sx_unlock(), but before the free_owner_pmcs() resulting in an assertion failure. free_owner_pmcs can't be protected by the scheduler lock because it may need to sleep waiting on sampling counters to come off the cpu. I'm not sure how to approach a fix other than disabling the KASSERT, and I'm not sure if that's safe. --=20 You are receiving this mail because: You are the assignee for the bug.=