Re: git: bb8441184bab - main - cam: don't lock while handling an AC_UNIT_ATTENTION

On Mon, Jan 3, 2022 at 7:02 PM Robert Wing <rew@freebsd.org> wrote:
>
> The branch main has been updated by rew:
>
> URL: https://cgit.FreeBSD.org/src/commit/?id=bb8441184bab60cd8a07c2b94bd6c4ae8b56ec25
>
> commit bb8441184bab60cd8a07c2b94bd6c4ae8b56ec25
> Author:     Robert Wing <rew@FreeBSD.org>
> AuthorDate: 2022-01-04 01:21:58 +0000
> Commit:     Robert Wing <rew@FreeBSD.org>
> CommitDate: 2022-01-04 01:56:48 +0000
>
>     cam: don't lock while handling an AC_UNIT_ATTENTION
>
>     Don't take the device_mtx lock in daasync() when handling an
>     AC_UNIT_ATTENTION. Instead, assert the lock is held before modifying the
>     periph's softc flags.
>
>     The device_mtx lock is taken in xptdevicetraverse() before daasync()
>     is eventually called in xpt_async_bcast().
>
>     PR:             240917, 226510, 226578
>     Reviewed by:    imp
>     MFC after:      3 weeks
>     Differential Revision: https://reviews.freebsd.org/D27735
> ---
>  sys/cam/scsi/scsi_da.c | 15 +++++----------
>  1 file changed, 5 insertions(+), 10 deletions(-)
>
> diff --git a/sys/cam/scsi/scsi_da.c b/sys/cam/scsi/scsi_da.c
> index 243e86d18caa..df8791e4b23e 100644
> --- a/sys/cam/scsi/scsi_da.c
> +++ b/sys/cam/scsi/scsi_da.c
> @@ -2158,7 +2158,7 @@ daasync(void *callback_arg, u_int32_t code,
>                 }
>                 break;
>         }
> -       case AC_UNIT_ATTENTION:
> +       case AC_UNIT_ATTENTION:         /* Called for this path: periph locked */
>         {
>                 union ccb *ccb;
>                 int error_code, sense_key, asc, ascq;
> @@ -2168,9 +2168,7 @@ daasync(void *callback_arg, u_int32_t code,
>
>                 /*
>                  * Handle all UNIT ATTENTIONs except our own, as they will be
> -                * handled by daerror(). Since this comes from a different periph,
> -                * that periph's lock is held, not ours, so we have to take it ours
> -                * out to touch softc flags.
> +                * handled by daerror().
>                  */
>                 if (xpt_path_periph(ccb->ccb_h.path) != periph &&
>                     scsi_extract_sense_ccb(ccb,
> @@ -2178,22 +2176,19 @@ daasync(void *callback_arg, u_int32_t code,
>                         if (asc == 0x2A && ascq == 0x09) {
>                                 xpt_print(ccb->ccb_h.path,
>                                     "Capacity data has changed\n");
> -                               cam_periph_lock(periph);
> +                               cam_periph_assert(periph, MA_OWNED);
>                                 softc->flags &= ~DA_FLAG_PROBED;
>                                 dareprobe(periph);
> -                               cam_periph_unlock(periph);
>                         } else if (asc == 0x28 && ascq == 0x00) {
> -                               cam_periph_lock(periph);
> +                               cam_periph_assert(periph, MA_OWNED);
>                                 softc->flags &= ~DA_FLAG_PROBED;
> -                               cam_periph_unlock(periph);
>                                 disk_media_changed(softc->disk, M_NOWAIT);
>                         } else if (asc == 0x3F && ascq == 0x03) {
>                                 xpt_print(ccb->ccb_h.path,
>                                     "INQUIRY data has changed\n");
> -                               cam_periph_lock(periph);
> +                               cam_periph_assert(periph, MA_OWNED);
>                                 softc->flags &= ~DA_FLAG_PROBED;
>                                 dareprobe(periph);
> -                               cam_periph_unlock(periph);
>                         }
>                 }
>                 break;

Thanks a lot!