[Mesa-dev] [PATCH 1/5] util/hash_table: Don't hash the deleted and freed keys

[Alyssa Rosenzweig]

To be clear, Panfrost relies on stuffing (bogus) magic numbers into u64
keys and u64 values. Is this going to break on us? That is, when you
mention this is a bug, who's buggy here? (Panfrost or hash_table_u64 or
both?)

On Mon, Aug 05, 2019 at 09:10:00AM -0700, Caio Marcelo de Oliveira Filho wrote:
> On Mon, Aug 05, 2019 at 05:18:32PM +0200, Tomeu Vizoso wrote:
> > Some hash functions (eg. key_u64_hash) will attempt to dereference the
> > key, causing an invalid access when passed DELETED_KEY_VALUE (0x1) or
> > FREED_KEY_VALUE (0x0).
> > 
> > The entry.hash field isn't needed by the delete_function, so just stop
> > populating it.
> 
> delete_function is a callback, so it is up to the caller whether it
> makes use it or not.  We also would have to add a comment somewhere
> about this exception.
> 
> Seems to me this is a bug of not calling hash correctly when
> `sizeof(void *) != 8`.  To fix we should do like in
> hash_table_u64_search() and create a temporary local struct
> hash_key_u64 in that case.
> 
> 
> 	Caio