When steal_context is used on SMP systems, it can steal a context in
use by one of the other processors. This patch adds context tracking to
prevent this as suggested by BenH.
Signed-off-by: Randy Vinson <[EMAIL PROTECTED]>
---
The previous version of this patch had some unnecessary code which has been
removed in this version.
Note: This is a proof-of-concept patch. This isn't my area of expertise,
so I'd greatly appreciate any guidance I can get. I'm considering the
use of for_each_online_cpu() instead of for_each_possible_cpu() and
possibly putting the changes under a CONFIG_SMP switch to prevent unnecessary
overhead in the non-SMP case.
arch/powerpc/mm/mmu_context_32.c | 29 ++++++++++++++++++++++++-----
include/asm-powerpc/mmu_context.h | 5 +++++
2 files changed, 29 insertions(+), 5 deletions(-)
diff --git a/arch/powerpc/mm/mmu_context_32.c b/arch/powerpc/mm/mmu_context_32.c
index cc32ba4..0dc7b83 100644
--- a/arch/powerpc/mm/mmu_context_32.c
+++ b/arch/powerpc/mm/mmu_context_32.c
@@ -34,6 +34,8 @@ unsigned long context_map[LAST_CONTEXT / BITS_PER_LONG + 1];
atomic_t nr_free_contexts;
struct mm_struct *context_mm[LAST_CONTEXT+1];
void steal_context(void);
+DEFINE_SPINLOCK(mm_lock);
+DEFINE_PER_CPU(struct mm_struct *, curr_mm);
#endif /* FEW_CONTEXTS */
/*
@@ -42,6 +44,9 @@ void steal_context(void);
void __init
mmu_context_init(void)
{
+#ifdef FEW_CONTEXTS
+ int cpu;
+#endif
/*
* Some processors have too few contexts to reserve one for
* init_mm, and require using context 0 for a normal task.
@@ -52,6 +57,8 @@ mmu_context_init(void)
next_mmu_context = FIRST_CONTEXT;
#ifdef FEW_CONTEXTS
atomic_set(&nr_free_contexts, LAST_CONTEXT - FIRST_CONTEXT + 1);
+ for_each_possible_cpu(cpu)
+ per_cpu(curr_mm, cpu) = NULL;
#endif /* FEW_CONTEXTS */
}
@@ -72,12 +79,24 @@ void
steal_context(void)
{
struct mm_struct *mm;
+ int cpu;
+
+ do {
+ /* free up context `next_mmu_context' */
+ /* if we shouldn't free context 0, don't... */
+ if (next_mmu_context < FIRST_CONTEXT)
+ next_mmu_context = FIRST_CONTEXT;
+ mm = context_mm[next_mmu_context];
+ for_each_possible_cpu(cpu) {
+ if ((cpu != smp_processor_id()) &&
+ per_cpu(curr_mm, cpu) == mm) {
+ mm = NULL;
+ next_mmu_context = (next_mmu_context + 1) &
+ LAST_CONTEXT;
+ }
+ }
+ } while(!mm);
- /* free up context `next_mmu_context' */
- /* if we shouldn't free context 0, don't... */
- if (next_mmu_context < FIRST_CONTEXT)
- next_mmu_context = FIRST_CONTEXT;
- mm = context_mm[next_mmu_context];
flush_tlb_mm(mm);
destroy_context(mm);
}
diff --git a/include/asm-powerpc/mmu_context.h
b/include/asm-powerpc/mmu_context.h
index 9102b8b..e083b25 100644
--- a/include/asm-powerpc/mmu_context.h
+++ b/include/asm-powerpc/mmu_context.h
@@ -113,6 +113,8 @@ extern unsigned long next_mmu_context;
extern atomic_t nr_free_contexts;
extern struct mm_struct *context_mm[LAST_CONTEXT+1];
extern void steal_context(void);
+extern spinlock_t mm_lock;
+DECLARE_PER_CPU(struct mm_struct *, curr_mm);
#endif
/*
@@ -125,6 +127,7 @@ static inline void get_mmu_context(struct mm_struct *mm)
if (mm->context.id != NO_CONTEXT)
return;
#ifdef FEW_CONTEXTS
+ spin_lock(&mm_lock);
while (atomic_dec_if_positive(&nr_free_contexts) < 0)
steal_context();
#endif
@@ -138,6 +141,8 @@ static inline void get_mmu_context(struct mm_struct *mm)
mm->context.id = ctx;
#ifdef FEW_CONTEXTS
context_mm[ctx] = mm;
+ per_cpu(curr_mm, smp_processor_id()) = mm;
+ spin_unlock(&mm_lock);
#endif
}
--
1.5.4.4.551.g1658c
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