Date: Thu, 8 Aug 2019 00:17:16 +0000 (UTC) From: Alexander Motin <mav@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-stable@freebsd.org, svn-src-stable-12@freebsd.org Subject: svn commit: r350703 - in stable/12/sys/cam: . scsi Message-ID: <201908080017.x780HGd1060174@repo.freebsd.org>
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Author: mav Date: Thu Aug 8 00:17:16 2019 New Revision: 350703 URL: https://svnweb.freebsd.org/changeset/base/350703 Log: MFC r340024 (by imp): 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: stable/12/sys/cam/cam_periph.c stable/12/sys/cam/scsi/scsi_da.c Directory Properties: stable/12/ (props changed) Modified: stable/12/sys/cam/cam_periph.c ============================================================================== --- stable/12/sys/cam/cam_periph.c Wed Aug 7 21:20:25 2019 (r350702) +++ stable/12/sys/cam/cam_periph.c Thu Aug 8 00:17:16 2019 (r350703) @@ -474,6 +474,12 @@ 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: stable/12/sys/cam/scsi/scsi_da.c ============================================================================== --- stable/12/sys/cam/scsi/scsi_da.c Wed Aug 7 21:20:25 2019 (r350702) +++ stable/12/sys/cam/scsi/scsi_da.c Thu Aug 8 00:17:16 2019 (r350703) @@ -2737,9 +2737,10 @@ 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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