svn commit: r328554 - head/sys/cam/scsi

[Dexuan-BSD Cui]

Hi imp and all,
I think this patch is very important, because it can fix a panic I
noticed recently when I try to hot-remove a SCSI disk from a VM
running on Azure/Hyper-V.

The panic is almost 100% reproducible with stable/11, but not in the
latest CURRENT code, so finally I identified this fix in the CURRENT
branch.

Can you please MFC this patch to 11 and 10?
It looks there is a major difference in the CAM code between 11/10
and the CURRENT code, and we may have to MFC more related patches. If
this is difficult, I hope at least we can provide a minimal re-written
version of the patch to 11 and 10?

Looking forward to your insight!

Thanks,
-- Dexuan


On Mon, Jan 29, 2018 at 10:07 AM, Warner Losh <imp at freebsd.org> wrote:
> Author: imp
> Date: Mon Jan 29 18:07:14 2018
> New Revision: 328554
> URL: https://svnweb.freebsd.org/changeset/base/328554
>
> Log:
>   Do the book-keeping on release before we release the reference. The
>   periph was going away on final release, and then returning and we
>   started dancing in free memory.
>
>   Sponsored by: Netflix
>
> Modified:
>   head/sys/cam/scsi/scsi_da.c
>
> Modified: head/sys/cam/scsi/scsi_da.c
> ==============================================================================
> --- head/sys/cam/scsi/scsi_da.c Mon Jan 29 17:32:30 2018        (r328553)
> +++ head/sys/cam/scsi/scsi_da.c Mon Jan 29 18:07:14 2018        (r328554)
> @@ -1549,12 +1549,12 @@ da_periph_unhold(struct cam_periph *periph, da_ref_tok
>         struct da_softc *softc = periph->softc;
>
>         token_sanity(token);
> -       cam_periph_unhold(periph);
>         DA_PERIPH_PRINT(periph, "Unholding device %s (%d)\n",
>             da_ref_text[token], token);
>         cnt = atomic_fetchadd_int(&softc->ref_flags[token], -1);
>         if (cnt != 1)
>                 panic("Unholding %d with cnt = %d", token, cnt);
> +       cam_periph_unhold(periph);
>  }
>
>  static inline int
> @@ -1583,12 +1583,12 @@ da_periph_release(struct cam_periph *periph, da_ref_to
>         struct da_softc *softc = periph->softc;
>
>         token_sanity(token);
> -       cam_periph_release(periph);
>         DA_PERIPH_PRINT(periph, "releasing device %s (%d)\n",
>             da_ref_text[token], token);
>         cnt = atomic_fetchadd_int(&softc->ref_flags[token], -1);
>         if (cnt != 1)
>                 panic("Releasing %d with cnt = %d", token, cnt);
> +       cam_periph_release(periph);
>  }
>
>  static inline void
> @@ -1598,12 +1598,12 @@ da_periph_release_locked(struct cam_periph *periph, da
>         struct da_softc *softc = periph->softc;
>
>         token_sanity(token);
> -       cam_periph_release_locked(periph);
>         DA_PERIPH_PRINT(periph, "releasing device (locked) %s (%d)\n",
>             da_ref_text[token], token);
>         cnt = atomic_fetchadd_int(&softc->ref_flags[token], -1);
>         if (cnt != 1)
>                 panic("Unholding %d with cnt = %d", token, cnt);
> +       cam_periph_release_locked(periph);
>  }
>
>  #define cam_periph_hold POISON
>