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authorBenjamin Herrenschmidt <benh@kernel.crashing.org>2009-05-19 16:56:42 +0000
committerBenjamin Herrenschmidt <benh@kernel.crashing.org>2009-06-09 16:42:21 +1000
commit3035c8634f0538a0c6946e3191bb6c9284b63798 (patch)
tree68f81301d2ced6492957c8320a631ad96518bd53 /arch/powerpc/mm
parentec097c84dff17511f2693e6ef6c3064dfbf0a3af (diff)
powerpc/mm: Fix some SMP issues with MMU context handling
This patch fixes a couple of issues that can happen as a result of steal_context() dropping the context_lock when all possible PIDs are ineligible for stealing (hopefully an extremely hard to hit occurence). This case exposes the possibility of a stale context_mm[] entry to be seen since destroy_context() doesn't clear it and the free map isn't re-tested. It also means steal_context() will not notice a context freed while the lock was help, thus possibly trying to steal a context when a free one was available. This fixes it by always returning to the caller from steal_context when it dropped the lock with a return value that causes the caller to re-samble the number of free contexts, along with properly clearing the context_mm[] array for destroyed contexts. Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Diffstat (limited to 'arch/powerpc/mm')
-rw-r--r--arch/powerpc/mm/mmu_context_nohash.c12
1 files changed, 8 insertions, 4 deletions
diff --git a/arch/powerpc/mm/mmu_context_nohash.c b/arch/powerpc/mm/mmu_context_nohash.c
index 030d0005b4d..c42858780cb 100644
--- a/arch/powerpc/mm/mmu_context_nohash.c
+++ b/arch/powerpc/mm/mmu_context_nohash.c
@@ -73,7 +73,6 @@ static unsigned int steal_context_smp(unsigned int id)
struct mm_struct *mm;
unsigned int cpu, max;
- again:
max = last_context - first_context;
/* Attempt to free next_context first and then loop until we manage */
@@ -108,7 +107,9 @@ static unsigned int steal_context_smp(unsigned int id)
spin_unlock(&context_lock);
cpu_relax();
spin_lock(&context_lock);
- goto again;
+
+ /* This will cause the caller to try again */
+ return MMU_NO_CONTEXT;
}
#endif /* CONFIG_SMP */
@@ -194,6 +195,8 @@ void switch_mmu_context(struct mm_struct *prev, struct mm_struct *next)
WARN_ON(prev->context.active < 1);
prev->context.active--;
}
+
+ again:
#endif /* CONFIG_SMP */
/* If we already have a valid assigned context, skip all that */
@@ -212,7 +215,8 @@ void switch_mmu_context(struct mm_struct *prev, struct mm_struct *next)
#ifdef CONFIG_SMP
if (num_online_cpus() > 1) {
id = steal_context_smp(id);
- goto stolen;
+ if (id == MMU_NO_CONTEXT)
+ goto again;
}
#endif /* CONFIG_SMP */
id = steal_context_up(id);
@@ -286,8 +290,8 @@ void destroy_context(struct mm_struct *mm)
mm->context.id = MMU_NO_CONTEXT;
#ifdef DEBUG_MAP_CONSISTENCY
mm->context.active = 0;
- context_mm[id] = NULL;
#endif
+ context_mm[id] = NULL;
nr_free_contexts++;
}
spin_unlock(&context_lock);