diff options
Diffstat (limited to 'kernel/dma')
| -rw-r--r-- | kernel/dma/swiotlb.c | 26 |
1 files changed, 20 insertions, 6 deletions
diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c index 85dd94323b98..01637677736f 100644 --- a/kernel/dma/swiotlb.c +++ b/kernel/dma/swiotlb.c @@ -728,9 +728,6 @@ static void swiotlb_dyn_alloc(struct work_struct *work) } add_mem_pool(mem, pool); - - /* Pairs with smp_rmb() in is_swiotlb_buffer(). */ - smp_wmb(); } /** @@ -1151,9 +1148,26 @@ static int swiotlb_find_slots(struct device *dev, phys_addr_t orig_addr, spin_unlock_irqrestore(&dev->dma_io_tlb_lock, flags); found: - dev->dma_uses_io_tlb = true; - /* Pairs with smp_rmb() in is_swiotlb_buffer() */ - smp_wmb(); + WRITE_ONCE(dev->dma_uses_io_tlb, true); + + /* + * The general barrier orders reads and writes against a presumed store + * of the SWIOTLB buffer address by a device driver (to a driver private + * data structure). It serves two purposes. + * + * First, the store to dev->dma_uses_io_tlb must be ordered before the + * presumed store. This guarantees that the returned buffer address + * cannot be passed to another CPU before updating dev->dma_uses_io_tlb. + * + * Second, the load from mem->pools must be ordered before the same + * presumed store. This guarantees that the returned buffer address + * cannot be observed by another CPU before an update of the RCU list + * that was made by swiotlb_dyn_alloc() on a third CPU (cf. multicopy + * atomicity). + * + * See also the comment in is_swiotlb_buffer(). + */ + smp_mb(); *retpool = pool; return index; |