On Tue, Oct 3, 2017 at 2:59 PM, Rob Clark <robdclark@xxxxxxxxx> wrote: > On Tue, Oct 3, 2017 at 4:08 AM, Daniel Vetter <daniel@xxxxxxxx> wrote: >> On Mon, Oct 02, 2017 at 10:37:11AM -0400, Rob Clark wrote: >>> Fixes intermittent corruption of cmdstream dump. >>> >>> Signed-off-by: Rob Clark <robdclark@xxxxxxxxx> >> >> Rule of memory barriers: They always need to come in pairs, and you should >> put a comment to each one explaining where the other side is. I.e. for all >> the store_release ones you add here you need to put a few read_acquire >> ones somewhere else, and then explain how they link. >> >> One side only doesn't really work with barriers - except when you're lucky >> and on x86 :-) > > fwiw, this is straight out of Documentation/circular-buffers.txt > > I guess it could read_acquire when checking the avail/free space on > the consumer/producer side.. otoh if we see an old value there it is > harmless (ie. we just fall into a wait_event()). I assume that is why > the documentation didn't bother with a read_acquire. smp_load_acquire is the right name, and it's right there. In the example at least :-) -Daniel > > BR, > -R > >> -Daniel >>> --- >>> drivers/gpu/drm/msm/msm_rd.c | 4 ++-- >>> 1 file changed, 2 insertions(+), 2 deletions(-) >>> >>> diff --git a/drivers/gpu/drm/msm/msm_rd.c b/drivers/gpu/drm/msm/msm_rd.c >>> index 5c087a4228ff..918c65e19964 100644 >>> --- a/drivers/gpu/drm/msm/msm_rd.c >>> +++ b/drivers/gpu/drm/msm/msm_rd.c >>> @@ -120,7 +120,7 @@ static void rd_write(struct msm_rd_state *rd, const void *buf, int sz) >>> 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; >>> >>> @@ -157,7 +157,7 @@ static ssize_t rd_read(struct file *file, char __user *buf, >>> 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); >>> -- >>> 2.13.5 >>> >>> _______________________________________________ >>> dri-devel mailing list >>> dri-devel@xxxxxxxxxxxxxxxxxxxxx >>> https://lists.freedesktop.org/mailman/listinfo/dri-devel >> >> -- >> Daniel Vetter >> Software Engineer, Intel Corporation >> http://blog.ffwll.ch -- Daniel Vetter Software Engineer, Intel Corporation +41 (0) 79 365 57 48 - http://blog.ffwll.ch -- To unsubscribe from this list: send the line "unsubscribe linux-arm-msm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
