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

[Mark Tinguely <tinguely@xxxxxxx>]

On 04/21/13 16:55, Eric Sandeen wrote:
> On 4/21/13 12:41 PM, Mark Tinguely wrote:
>
> > This problem happened locally with a bad inode number from xfs
> > recovery. xfs_perag_get() can return NULL if given a bad agno.
> > Most callers of xfs_perag_get() do not check for a NULL before
> > using the pointer. This patch forces a shutdown of the filesystem
> > for those callers that do not check the return value rather than
> > crashing on a dereferenced NULL pointer.
> Hi Mark -
>
> I'm curious, what was the callchain when this happened?  Was it
> during recovery?  If so, would aborting recovery be more prudent?
>
> I might be missing something, but I'm not sure how shutting
> down avoids a subsequent null ptr deref&  crash.
>
> i.e. if a caller does something like:
>
>          pag = xfs_perag_get(mp, agno);
>          spin_lock(&pag->pagb_lock);
>
> shutting down in xfs_perag_get doesn't save us from a
> null pag pointer, would it?
>
> Thanks,
> -Eric
You are correct, we have to exit the routine(s) to avoid the 
dereference. Let the callers handle the error.
Sorry for the noise.

--Mark.