drm/msm: use proper memory barriers for updating tail/head

Fixes intermittent corruption of cmdstream dump.

Signed-off-by: Rob Clark <robdclark@gmail.com>

diff --git a/drivers/gpu/drm/msm/msm_rd.c b/drivers/gpu/drm/msm/msm_rd.c
index 0366b8092f9772178334449ce121255087206ede..ec56794ad0399277693b9185c75b6abcf9241e4a 100644 (file)
--- a/drivers/gpu/drm/msm/msm_rd.c
+++ b/drivers/gpu/drm/msm/msm_rd.c
@@ -111,10 +111,14 @@ static void rd_write(struct msm_rd_state *rd, const void *buf, int sz)
 
                wait_event(rd->fifo_event, circ_space(&rd->fifo) > 0);
 
+               /* Note that smp_load_acquire() is not strictly required
+                * as CIRC_SPACE_TO_END() does not access the tail more
+                * than once.
+                */
                n = min(sz, circ_space_to_end(&rd->fifo));
                memcpy(fptr, ptr, n);
 
-               fifo->head = (fifo->head + n) & (BUF_SZ - 1);
+               smp_store_release(&fifo->head, (fifo->head + n) & (BUF_SZ - 1));
                sz  -= n;
                ptr += n;
 
@@ -145,13 +149,17 @@ static ssize_t rd_read(struct file *file, char __user *buf,
        if (ret)
                goto out;
 
+       /* Note that smp_load_acquire() is not strictly required
+        * as CIRC_CNT_TO_END() does not access the head more than
+        * once.
+        */
        n = min_t(int, sz, circ_count_to_end(&rd->fifo));
        if (copy_to_user(buf, fptr, n)) {
                ret = -EFAULT;
                goto out;
        }
 
-       fifo->tail = (fifo->tail + n) & (BUF_SZ - 1);
+       smp_store_release(&fifo->tail, (fifo->tail + n) & (BUF_SZ - 1));
        *ppos += n;
 
        wake_up_all(&rd->fifo_event);