Re: [PREVIEW] Avoid memory corruption and segfaults during ufs cache store maintenance

On 26.07.2012 12:33, Alex Rousskov wrote:
> Hello,
>
> The attached patch avoids memory corruption and segfaults during
> ufs
> cache store maintenance by removing being-deleted StoreEntry from ufs
> cache replacement policies.
>
> SMP Store changes added a SwapDir::disconnect() method that notified
> entry's cache_dir that its entry is being destroyed. I added that
> code
> so that shared cache_dirs can update their index when idle
> store_table
> entries are destroyed on cleanup (completely avoiding idle entries
> proved to be too difficult with store_table still around).
>
> However, I did not realize that non-shared cache_dirs have the same
> problem: Their StoreEntries may be deleted without cache_dirs knowing
> that. UFS cache_dir now implement the SwapDir::disconnect() API to
> stay
> in sync. It is likely that the problem was introduced by SMP Store
> changes, but I do not know whether there is a better fix for it.
>
> I also added assertions to catch cases where a dirty StoreEntry or
> MemObject (i.e., an entry or object that is still in some replacement
> policy index) is being destroyed.
>
>
> TODO: This patch breaks "make check". We need more STUBs somewhere!
>
>
> Alex.

I've been thinking for some time that we need to implement a list of
being-deleted entries in each cache and add a unlinkd response handler
to erase them from that list after actual deletion which unregisters the
fileno for re-use.

Amos
Received on Thu Jul 26 2012 - 03:17:21 MDT