Date: Thu, 1 Nov 2018 21:51:42 +0000 (UTC) From: Warner Losh <imp@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r340024 - in head/sys/cam: . scsi Message-ID: <201811012151.wA1Lpgtj019844@repo.freebsd.org>
next in thread | raw e-mail | index | archive | help
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. */
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?201811012151.wA1Lpgtj019844>