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. 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 _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
