Author: markj
Date: Sat Nov 24 17:09:35 2018
New Revision: 340903
URL: https://svnweb.freebsd.org/changeset/base/340903
Log:
MFC r340734:
Avoid unsynchronized updates to kn_status.
Modified:
stable/12/sys/kern/kern_event.c
Directory Properties:
stable/12/ (props changed)
Modified: stable/12/sys/kern/kern_event.c
==============================================================================
--- stable/12/sys/kern/kern_event.c Sat Nov 24 17:08:49 2018
(r340902)
+++ stable/12/sys/kern/kern_event.c Sat Nov 24 17:09:35 2018
(r340903)
@@ -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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