Author: imp
Date: Thu Nov 1 21:51:41 2018
New Revision: 340024
URL: https://svnweb.freebsd.org/changeset/base/340024
Log:
Add comments explaining what hold/unhold do
They act as a simple one-deep semaphore to keep open/close/probe from
running at the same time to avoid races that creates.
Modified:
head/sys/cam/cam_periph.c
head/sys/cam/scsi/scsi_da.c
Modified: head/sys/cam/cam_periph.c
==============================================================================
--- head/sys/cam/cam_periph.c Thu Nov 1 21:49:49 2018 (r340023)
+++ head/sys/cam/cam_periph.c Thu Nov 1 21:51:41 2018 (r340024)
@@ -470,6 +470,12 @@ cam_periph_release(struct cam_periph *periph)
mtx_unlock(mtx);
}
+/*
+ * hold/unhold act as mutual exclusion for sections of the code that
+ * need to sleep and want to make sure that other sections that
+ * will interfere are held off. This only protects exclusive sections
+ * from each other.
+ */
int
cam_periph_hold(struct cam_periph *periph, int priority)
{
Modified: head/sys/cam/scsi/scsi_da.c
==============================================================================
--- head/sys/cam/scsi/scsi_da.c Thu Nov 1 21:49:49 2018 (r340023)
+++ head/sys/cam/scsi/scsi_da.c Thu Nov 1 21:51:41 2018 (r340024)
@@ -2697,9 +2697,10 @@ daregister(struct cam_periph *periph, void *arg)
TASK_INIT(&softc->sysctl_task, 0, dasysctlinit, periph);
/*
- * Take an exclusive refcount on the periph while dastart is called
- * to finish the probe. The reference will be dropped in dadone at
- * the end of probe.
+ * Take an exclusive section lock qon the periph while dastart is called
+ * to finish the probe. The lock will be dropped in dadone at the end
+ * of probe. This locks out daopen and daclose from racing with the
+ * probe.
*
* XXX if cam_periph_hold returns an error, we don't hold a refcount.
*/
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