get_cpu() disables preemption and returns the current CPU number. The
CPU number is only used once while retrieving the address of the local's
CPU deferred_flush pointer.
We can instead use raw_cpu_ptr() while we remain preemptible. The worst
thing that can happen is that flush_unmaps_timeout() is invoked multiple
times: once by taskA after seeing HIGH_WATER_MARK and then preempted to
another CPU and then by taskB which saw HIGH_WATER_MARK on the same CPU
as taskA. It is also likely that ->size got from HIGH_WATER_MARK to 0
right after its read because another CPU invoked flush_unmaps_timeout()
for this CPU.
The access to flush_data is protected by a spinlock so even if we get
migrated to another CPU or preempted - the data structure is protected.
While at it, I marked deferred_flush static since I can't find a
reference to it outside of this file.
Cc: David Woodhouse <dw...@infradead.org>
Cc: Joerg Roedel <j...@8bytes.org>
Cc: iommu@lists.linux-foundation.org
Cc: Andrew Morton <a...@linux-foundation.org>
Signed-off-by: Sebastian Andrzej Siewior <bige...@linutronix.de>
---
drivers/iommu/intel-iommu.c | 8 ++------
1 file changed, 2 insertions(+), 6 deletions(-)
diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
index 8500deda9175..1c7118d1525e 100644
--- a/drivers/iommu/intel-iommu.c
+++ b/drivers/iommu/intel-iommu.c
@@ -481,7 +481,7 @@ struct deferred_flush_data {
struct deferred_flush_table *tables;
};
-DEFINE_PER_CPU(struct deferred_flush_data, deferred_flush);
+static DEFINE_PER_CPU(struct deferred_flush_data, deferred_flush);
/* bitmap for indexing intel_iommus */
static int g_num_of_iommus;
@@ -3725,10 +3725,8 @@ static void add_unmap(struct dmar_domain *dom, unsigned
long iova_pfn,
struct intel_iommu *iommu;
struct deferred_flush_entry *entry;
struct deferred_flush_data *flush_data;
- unsigned int cpuid;
- cpuid = get_cpu();
- flush_data = per_cpu_ptr(&deferred_flush, cpuid);
+ flush_data = raw_cpu_ptr(&deferred_flush);
/* Flush all CPUs' entries to avoid deferring too much. If
* this becomes a bottleneck, can just flush us, and rely on
@@ -3761,8 +3759,6 @@ static void add_unmap(struct dmar_domain *dom, unsigned
long iova_pfn,
}
flush_data->size++;
spin_unlock_irqrestore(&flush_data->lock, flags);
-
- put_cpu();
}
static void intel_unmap(struct device *dev, dma_addr_t dev_addr, size_t size)
--
2.13.1
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