Date: Sat, 24 Nov 2018 17:11:48 +0000 (UTC) From: Mark Johnston <markj@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-stable@freebsd.org, svn-src-stable-11@freebsd.org Subject: svn commit: r340904 - stable/11/sys/kern Message-ID: <201811241711.wAOHBmMD012641@repo.freebsd.org>
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Author: markj Date: Sat Nov 24 17:11:47 2018 New Revision: 340904 URL: https://svnweb.freebsd.org/changeset/base/340904 Log: MFC r340734: Avoid unsynchronized updates to kn_status. Modified: stable/11/sys/kern/kern_event.c Directory Properties: stable/11/ (props changed) Modified: stable/11/sys/kern/kern_event.c ============================================================================== --- stable/11/sys/kern/kern_event.c Sat Nov 24 17:09:35 2018 (r340903) +++ stable/11/sys/kern/kern_event.c Sat Nov 24 17:11:47 2018 (r340904) @@ -1391,6 +1391,8 @@ findkn: kn->kn_kevent.flags &= ~(EV_ADD | EV_DELETE | EV_ENABLE | EV_DISABLE | EV_FORCEONESHOT); kn->kn_status = KN_INFLUX|KN_DETACHED; + if ((kev->flags & EV_DISABLE) != 0) + kn->kn_status |= KN_DISABLED; error = knote_attach(kn, kq); KQ_UNLOCK(kq); @@ -1427,6 +1429,11 @@ findkn: KNOTE_ACTIVATE(kn, 1); } + if ((kev->flags & EV_ENABLE) != 0) + kn->kn_status &= ~KN_DISABLED; + else if ((kev->flags & EV_DISABLE) != 0) + kn->kn_status |= KN_DISABLED; + /* * The user may change some filter values after the initial EV_ADD, * but doing so will not reset any filter which has already been @@ -1443,19 +1450,17 @@ findkn: kn->kn_sdata = kev->data; } +done_ev_add: /* * We can get here with kn->kn_knlist == NULL. This can happen when * the initial attach event decides that the event is "completed" - * already. i.e. filt_procattach is called on a zombie process. It - * will call filt_proc which will remove it from the list, and NULL + * already, e.g., filt_procattach() is called on a zombie process. It + * will call filt_proc() which will remove it from the list, and NULL * kn_knlist. + * + * KN_DISABLED will be stable while the knote is in flux, so the + * unlocked read will not race with an update. */ -done_ev_add: - if ((kev->flags & EV_ENABLE) != 0) - kn->kn_status &= ~KN_DISABLED; - else if ((kev->flags & EV_DISABLE) != 0) - kn->kn_status |= KN_DISABLED; - if ((kn->kn_status & KN_DISABLED) == 0) event = kn->kn_fop->f_event(kn, 0); else
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