Date: Mon, 26 Nov 2018 15:46:46 +0000 (UTC) From: Mark Johnston <markj@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-releng@freebsd.org Subject: svn commit: r340977 - releng/12.0/sys/kern Message-ID: <201811261546.wAQFkkw7060706@repo.freebsd.org>
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Author: markj Date: Mon Nov 26 15:46:46 2018 New Revision: 340977 URL: https://svnweb.freebsd.org/changeset/base/340977 Log: MFstable/12 r340903: Avoid unsynchronized updates to kn_status. Approved by: re (gjb) Modified: releng/12.0/sys/kern/kern_event.c Directory Properties: releng/12.0/ (props changed) Modified: releng/12.0/sys/kern/kern_event.c ============================================================================== --- releng/12.0/sys/kern/kern_event.c Mon Nov 26 15:33:55 2018 (r340976) +++ releng/12.0/sys/kern/kern_event.c Mon Nov 26 15:46:46 2018 (r340977) @@ -1535,6 +1535,8 @@ findkn: kn->kn_kevent.flags &= ~(EV_ADD | EV_DELETE | EV_ENABLE | EV_DISABLE | EV_FORCEONESHOT); kn->kn_status = KN_DETACHED; + if ((kev->flags & EV_DISABLE) != 0) + kn->kn_status |= KN_DISABLED; kn_enter_flux(kn); error = knote_attach(kn, kq); @@ -1570,6 +1572,11 @@ 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 @@ -1587,19 +1594,17 @@ 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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