On Wed, Sep 23, 2009 at 02:27:26PM -0400, Randy MacLeod wrote: > I'd like advice on changing the implementation of smp_processor_id on > Cavium specifically and/or MIPS generally. > > Currently we have: arch/mips/include/asm/smp.h > #define raw_smp_processor_id() (current_thread_info()->cpu) > > A co-worker has an issue where the current thread pointer is corrupted > on a Cavium MIPS system running 2.6.14 (but the same code exists in 2.6.31). > During the resulting panic() the kernel calls smp_processor_id() > which dereferences the corrupt task pointer again - ouch. I've notice that > other arches have raw_smp_processor_id() defined to > - a platform specific register read, or > - a percpu variable or > - have a hard_smp_processor_id() defined > This last one is presumably for times when you don't trust the kernel > data structures to be > sane. Dereferencing current_thread_info()->cpu is fairly likely to hit in the cache so probably a single cycle operation. raw_smp_processor_id() is also a very common operation so you really don't want to change it to something slower except for a debugging kernel. If you have a good kernel stack pointer you can compute the thread pointer from that: ori $28, sp, _THREAD_MASK xori $28, _THREAD_MASK > I can create a patch that calls cvmx_get_core_num(); for cavium. > Is there a more generic way to get the cpu number on MIPS? raw_smp_processor_id() returns the processor ID as counted by Linux. That number does not necessarily match the firmware's numbering. Ralf
