[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 <hugh@veritas.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/asm-sparc64/mmu_context.h b/include/asm-sparc64/mmu_context.h
index 87c43c6..08ba72d 100644
--- a/include/asm-sparc64/mmu_context.h
+++ b/include/asm-sparc64/mmu_context.h
@@ -87,37 +87,35 @@
static inline void switch_mm(struct mm_struct *old_mm, struct mm_struct *mm, struct task_struct *tsk)
{
unsigned long ctx_valid;
+ int cpu;
+ /* Note: page_table_lock is used here to serialize switch_mm
+ * and activate_mm, and their calls to get_new_mmu_context.
+ * This use of page_table_lock is unrelated to its other uses.
+ */
spin_lock(&mm->page_table_lock);
- if (CTX_VALID(mm->context))
- ctx_valid = 1;
- else
- ctx_valid = 0;
+ ctx_valid = CTX_VALID(mm->context);
+ if (!ctx_valid)
+ get_new_mmu_context(mm);
+ spin_unlock(&mm->page_table_lock);
if (!ctx_valid || (old_mm != mm)) {
- if (!ctx_valid)
- get_new_mmu_context(mm);
-
load_secondary_context(mm);
reload_tlbmiss_state(tsk, mm);
}
- {
- int cpu = smp_processor_id();
-
- /* Even if (mm == old_mm) we _must_ check
- * the cpu_vm_mask. If we do not we could
- * corrupt the TLB state because of how
- * smp_flush_tlb_{page,range,mm} on sparc64
- * and lazy tlb switches work. -DaveM
- */
- if (!ctx_valid || !cpu_isset(cpu, mm->cpu_vm_mask)) {
- cpu_set(cpu, mm->cpu_vm_mask);
- __flush_tlb_mm(CTX_HWBITS(mm->context),
- SECONDARY_CONTEXT);
- }
+ /* Even if (mm == old_mm) we _must_ check
+ * the cpu_vm_mask. If we do not we could
+ * corrupt the TLB state because of how
+ * smp_flush_tlb_{page,range,mm} on sparc64
+ * and lazy tlb switches work. -DaveM
+ */
+ cpu = smp_processor_id();
+ if (!ctx_valid || !cpu_isset(cpu, mm->cpu_vm_mask)) {
+ cpu_set(cpu, mm->cpu_vm_mask);
+ __flush_tlb_mm(CTX_HWBITS(mm->context),
+ SECONDARY_CONTEXT);
}
- spin_unlock(&mm->page_table_lock);
}
#define deactivate_mm(tsk,mm) do { } while (0)
@@ -127,6 +125,10 @@
{
int cpu;
+ /* Note: page_table_lock is used here to serialize switch_mm
+ * and activate_mm, and their calls to get_new_mmu_context.
+ * This use of page_table_lock is unrelated to its other uses.
+ */
spin_lock(&mm->page_table_lock);
if (!CTX_VALID(mm->context))
get_new_mmu_context(mm);