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 --- kernel/fork.c | 7 ------- 1 file changed, 7 deletions(-) (limited to 'kernel/fork.c') diff --git a/kernel/fork.c b/kernel/fork.c index efac2c5..158710d 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -470,13 +470,6 @@ static int copy_mm(unsigned long clone_flags, struct task_struct * tsk) if (clone_flags & CLONE_VM) { atomic_inc(&oldmm->mm_users); mm = oldmm; - /* - * There are cases where the PTL is held to ensure no - * new threads start up in user mode using an mm, which - * allows optimizing out ipis; the tlb_gather_mmu code - * is an example. - */ - spin_unlock_wait(&oldmm->page_table_lock); goto good_mm; } -- cgit v1.1