On 05/18, David Howells wrote: > > This doesn't break cached copies of current, whether they're cached by gcc in > registers or on the stack. switch_to() will save all registers on the stack > before actually switching, then when it switches current, it will also switch > the stack and then pop back what was stored in the 'unclobbered' registers for > the now active task and stack. Thus the copies of current that were cached > just work. > > [...snip...] > > --- a/include/asm-generic/current.h > +++ b/include/asm-generic/current.h > @@ -3,7 +3,14 @@ > > #include <linux/thread_info.h> > > -#define get_current() (current_thread_info()->task) > +struct task_struct; > + > +static inline __attribute_const__ > +struct task_struct *get_current(void) > +{ > + return current_thread_info()->task; > +} Can't ack this patch, but it looks correct to me. And, looking at this patch I think that schedule() can be simplified a little bit. "sched: Reassign prev and switch_count when reacquire_kernel_lock() fail" commit 6d558c3ac9b6508d26fd5cadccce51fc9d726b1c says: Assume A->B schedule is processing, ... Then on B's context, ... prev and switch_count are related to A How so? switch_count - yes, we should change it. But prev must be equal to B, and it must be equal to current. When we return from switch_to() registers/stack should be restored correctly, so we can do --- x/kernel/sched.c +++ x/kernel/sched.c @@ -3729,8 +3729,7 @@ need_resched_nonpreemptible: post_schedule(rq); - if (unlikely(reacquire_kernel_lock(current) < 0)) { - prev = rq->curr; + if (unlikely(reacquire_kernel_lock(prev) < 0)) { switch_count = &prev->nivcsw; goto need_resched_nonpreemptible; } and in fact we can simplify this even more, no need to reassign switch_count, we can just move the initial assignment down, under "need_resched_nonpreemptible" label. switch_to(prev, next, prev) changes "prev" inside context_switch() but it should be stable inside of schedule(). Oleg. --- x/kernel/sched.c +++ x/kernel/sched.c @@ -3708,7 +3708,6 @@ need_resched: rq = cpu_rq(cpu); rcu_sched_qs(cpu); prev = rq->curr; - switch_count = &prev->nivcsw; release_kernel_lock(prev); need_resched_nonpreemptible: @@ -3722,6 +3721,7 @@ need_resched_nonpreemptible: update_rq_clock(rq); clear_tsk_need_resched(prev); + switch_count = &prev->nivcsw; if (prev->state && !(preempt_count() & PREEMPT_ACTIVE)) { if (unlikely(signal_pending_state(prev->state, prev))) prev->state = TASK_RUNNING; @@ -3758,11 +3758,8 @@ need_resched_nonpreemptible: post_schedule(rq); - if (unlikely(reacquire_kernel_lock(current) < 0)) { - prev = rq->curr; - switch_count = &prev->nivcsw; + if (unlikely(reacquire_kernel_lock(prev)) goto need_resched_nonpreemptible; - } preempt_enable_no_resched(); if (need_resched()) -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html