Re: [PATCH] xfs: shutdown filesystem if xfs_perag_get fails

[Mark Tinguely <tinguely@sgi.com>]

On 04/25/13 17:41, Chandra Seetharaman wrote:
> In which case something along the lines of
>
> ---
> diff --git a/fs/xfs/xfs_mount.c b/fs/xfs/xfs_mount.c
> index 3806088..3fb2fa6 100644
> --- a/fs/xfs/xfs_mount.c
> +++ b/fs/xfs/xfs_mount.c
> @@ -203,7 +203,13 @@ xfs_perag_get(struct xfs_mount *mp, xfs_agnumber_t
> agno)
>          if (pag) {
>                  ASSERT(atomic_read(&pag->pag_ref)>= 0);
>                  ref = atomic_inc_return(&pag->pag_ref);
> -       }
> +       } else
> +               /*
> +                * xfs_perag_get() is called with invalid agno,
> +                * which cannot happen. This indicates a problem
> +                * in the calling code.
> +                */
> +               BUG();
>          rcu_read_unlock();
>          trace_xfs_perag_get(mp, agno, ref, _RET_IP_);
>          return pag;
> --------
>
> would be useful ?. Since we have a NULL pag, we will trip somewhere
> else. At least with this, there is a pointer to the debugger/sysadmin
> about where/what to look for (may be with more valuable/correct comment
> than above).
>

We will have to make sure the callers of xfs_perag_get() handle the NULL
before dereferencing it. Sometimes the NULL is normal and just means the
perag structure has not been initialize yet.

Properly handling the NULL from xfs_perag_get() in the caller will also
mean that the callers of the callers of xfs_perag_get() have to handle
the NULL returned to them. I will come back to this once the CRC stuff
has been put to rest.

--Mark.

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