ioat: close potential BUG_ON race in the descriptor cleanup path

Since ioat_cleanup_preamble() and the update of the last completed
descriptor are not synchronized there is a chance that two cleanup threads
can see descriptors to clean.  If the first cleans up all pending
descriptors then the second will trigger the BUG_ON.

Signed-off-by: Dan Williams <dan.j.williams@intel.com>

2 files changed, 2 insertions, 2 deletions

diff --git a/drivers/dma/ioat/dma_v2.c b/drivers/dma/ioat/dma_v2.c
index c6e4531fe524..01ed1cfd3eb6 100644
--- a/drivers/dma/ioat/dma_v2.c
+++ b/drivers/dma/ioat/dma_v2.c
@@ -158,7 +158,7 @@ static void __cleanup(struct ioat2_dma_chan *ioat, unsigned long phys_complete)
                         seen_current = true;
         }
         ioat->tail += i;
-        BUG_ON(!seen_current); /* no active descs have written a completion? */
+        BUG_ON(active && !seen_current); /* no active descs have written a completion? */
 
         chan->last_completion = phys_complete;
         if (ioat->head == ioat->tail) {
diff --git a/drivers/dma/ioat/dma_v3.c b/drivers/dma/ioat/dma_v3.c
index bff48e8cffc4..39520f2f7da9 100644
--- a/drivers/dma/ioat/dma_v3.c
+++ b/drivers/dma/ioat/dma_v3.c
@@ -293,7 +293,7 @@ static void __cleanup(struct ioat2_dma_chan *ioat, unsigned long phys_complete)
                 }
         }
         ioat->tail += i;
-        BUG_ON(!seen_current); /* no active descs have written a completion? */
+        BUG_ON(active && !seen_current); /* no active descs have written a completion? */
         chan->last_completion = phys_complete;
         if (ioat->head == ioat->tail) {
                 dev_dbg(to_dev(chan), "%s: cancel completion timeout\n",