On 01/05/15 18:37, John Baldwin wrote:
On 1/2/15 8:35 AM, Hans Petter Selasky wrote:
Author: hselasky
Date: Fri Jan 2 13:35:10 2015
New Revision: 276534
URL: https://svnweb.freebsd.org/changeset/base/276534
Log:
The "vt_suspend_flush_timer()" function is sometimes called locked
which prevents us from doing a "callout_drain()" call. The callout in
question has a lock associated with it and we are not freeing the
callout. That means we can use the "callout_stop()" function to
atomically stop the callback iff the "callout_stop()" function is
called locked. This patch applies proper locking to "callout_stop()"
and replaces a "callout_drain()" with a "callout_stop()".
Modified: head/sys/dev/vt/vt_core.c
==============================================================================
--- head/sys/dev/vt/vt_core.c Fri Jan 2 13:15:36 2015 (r276533)
+++ head/sys/dev/vt/vt_core.c Fri Jan 2 13:35:10 2015 (r276534)
@@ -114,6 +114,7 @@ const struct terminal_class vt_termclass
#define VT_LOCK(vd) mtx_lock(&(vd)->vd_lock)
#define VT_UNLOCK(vd) mtx_unlock(&(vd)->vd_lock)
+#define VT_LOCK_ASSERT(vd, what) mtx_assert(&(vd)->vd_lock, what)
#define VT_UNIT(vw) ((vw)->vw_device->vd_unit * VT_MAXWINDOWS + \
(vw)->vw_number)
@@ -283,12 +284,18 @@ vt_resume_flush_timer(struct vt_device *
static void
vt_suspend_flush_timer(struct vt_device *vd)
{
+ /*
+ * As long as this function is called locked, callout_stop()
+ * has the same effect like callout_drain() with regard to
+ * preventing the callback function from executing.
+ */
+ VT_LOCK_ASSERT(vd, MA_OWNED);
Note that this assert is redundant. callout_stop() already asserts this
for a callout initialized via callout_init_mtx().
Right, but there is an "if" there which not always makes the assert
visible execept for static code analysis.
--HPS
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