Hi again, So, various versions of GCC can trigger/untrigger the RCU bugs that I've been hitting. This may of course still be due to GCC miscompiling some code on alpha but that said I've taken another look at the code involved when this is triggered. From what I've seen so far, this happens when kernel threads are used in the code to access structured data stored on the stack (structs). The quote below is from a comment in the kernel code (include/linux/percpu-defs.h) "s390 and alpha modules require percpu variables to be defined as weak to force the compiler to generate GOT based external references for them. This is necessary because percpu sections will be located outside of the usually addressable area. This definition puts the following two extra restrictions when defining percpu variables. 1. The symbol must be globally unique, even the static ones. 2. Static percpu variables cannot be defined inside a function." Taking these notes into account I've made some minor modifications to the code (briefly described below). The modifications involve declaring some structs previously placed on stack as DEFINE_PER_CPU_SHARED_ALIGNED. This is already done for some strucs in rcu/smp code. Making these modifications fixes the problem and I can build the kernel with GCC versions that previously triggered the bug. The same approach fixed both the network interface-rename bug as well as the scsi module unload bug. in kernel/smp/smp.c ------------------- #if defined(ARCH_NEEDS_WEAK_PER_CPU) smp_call_function_single(...) use csd = this_cpu_ptr(&csd_data) regardless if its called with wait = 0 or 1. Make sure to declare csd_data as "DEFINE_PER_CPU_SHARED_ALIGNED" #endif in kernel/rcu/tree.c -------------------- #use rew_data instead of stack allocated struct static DEFINE_PER_CPU_SHARED_ALIGNED(struct rcu_exp_work, rew_data); in kernel/rcu/tree_exp.h ------------------------ #if defined(ARCH_NEEDS_WEAK_PER_CPU) void synchronize_rcu_expedited(void) in stead of: struct rcu_exp_work rew; do: #if defined(ARCH_NEEDS_WEAK_PER_CPU) struct rcu_exp_work *rewp; rewp=this_cpu_ptr(&rew_data); rew_data is declared "DEFINE_PER_CPU_SHARED_ALIGNED" #endif /Magnus
