From dedeb0029b9c83420fc1337d4ee53daa7b2a0ad4 Mon Sep 17 00:00:00 2001 From: Hugh Dickins Date: Mon, 7 Nov 2005 14:09:01 -0800 Subject: [SPARC64] mm: context switch ptlock sparc64 is unique among architectures in taking the page_table_lock in its context switch (well, cris does too, but erroneously, and it's not yet SMP anyway). This seems to be a private affair between switch_mm and activate_mm, using page_table_lock as a per-mm lock, without any relation to its uses elsewhere. That's fine, but comment it as such; and unlock sooner in switch_mm, more like in activate_mm (preemption is disabled here). There is a block of "if (0)"ed code in smp_flush_tlb_pending which would have liked to rely on the page_table_lock, in switch_mm and elsewhere; but its comment explains how dup_mmap's flush_tlb_mm defeated it. And though that could have been changed at any time over the past few years, now the chance vanishes as we push the page_table_lock downwards, and perhaps split it per page table page. Just delete that block of code. Which leaves the mysterious spin_unlock_wait(&oldmm->page_table_lock) in kernel/fork.c copy_mm. Textual analysis (supported by Nick Piggin) suggests that the comment was written by DaveM, and that it relates to the defeated approach in the sparc64 smp_flush_tlb_pending. Just delete this block too. Signed-off-by: Hugh Dickins Signed-off-by: David S. Miller --- arch/sparc64/kernel/smp.c | 31 +++++-------------------------- 1 file changed, 5 insertions(+), 26 deletions(-) (limited to 'arch/sparc64/kernel/smp.c') diff --git a/arch/sparc64/kernel/smp.c b/arch/sparc64/kernel/smp.c index b137fd63f5e1..a9089e2140e9 100644 --- a/arch/sparc64/kernel/smp.c +++ b/arch/sparc64/kernel/smp.c @@ -883,34 +883,13 @@ void smp_flush_tlb_pending(struct mm_struct *mm, unsigned long nr, unsigned long u32 ctx = CTX_HWBITS(mm->context); int cpu = get_cpu(); - if (mm == current->active_mm && atomic_read(&mm->mm_users) == 1) { + if (mm == current->active_mm && atomic_read(&mm->mm_users) == 1) mm->cpu_vm_mask = cpumask_of_cpu(cpu); - goto local_flush_and_out; - } else { - /* This optimization is not valid. Normally - * we will be holding the page_table_lock, but - * there is an exception which is copy_page_range() - * when forking. The lock is held during the individual - * page table updates in the parent, but not at the - * top level, which is where we are invoked. - */ - if (0) { - cpumask_t this_cpu_mask = cpumask_of_cpu(cpu); - - /* By virtue of running under the mm->page_table_lock, - * and mmu_context.h:switch_mm doing the same, the - * following operation is safe. - */ - if (cpus_equal(mm->cpu_vm_mask, this_cpu_mask)) - goto local_flush_and_out; - } - } - - smp_cross_call_masked(&xcall_flush_tlb_pending, - ctx, nr, (unsigned long) vaddrs, - mm->cpu_vm_mask); + else + smp_cross_call_masked(&xcall_flush_tlb_pending, + ctx, nr, (unsigned long) vaddrs, + mm->cpu_vm_mask); -local_flush_and_out: __flush_tlb_pending(ctx, nr, vaddrs); put_cpu(); -- cgit v1.2.3