Hi! I just wanted to let people on this list know that turning slab debugging may cause slab corruption on non-coherent cache CPUs (4xx, 8xx).
The reason for this is that usually drivers which use DMA assume L1 cache line alignment for buffers (e.g. returned from alloc_skb). Unfortunately, with slab debugging enabled this is no longer the case, and during cache invalidates we corrupt slab cache (or at least slab poison markers). I tried to define ARCH_KMALLOC_MINALIGN and/or ARCH_SLAB_MINALIGN but it didn't work (and even if it did, it'd effectively disabled slab debugging anyway). I don't understand why slab debugging feature has to change allocation alignment, as it can be obviously implemented without breaking this alignment. Probably the reason is the usual one - nobody cares/cared about non-coherent cache CPUs and saving couple of bytes was more important :). Anyway, I made a hack for my EMAC driver: http://kernel.ebshome.net/emac_slab_debug.diff which helps with this problem, although other drivers may experience the same problem when used on 4xx/8xx with slab debugging enabled. In fact, 3COM 905 driver crashed Ocotea in this configuration too. -- Eugene
