4.4-stable review patch. If anyone has any objections, please let me know. ------------------ From: Akash Goel <akash.goel@xxxxxxxxx> commit d43f3ebf12f59c57782ec652da65ef61c2662b40 upstream. Currently for the case where there is enough space at the end of Ring buffer for accommodating only the base request, the wrapround is done immediately and as a result the base request gets added at the start of Ring buffer. But there may not be enough free space at the beginning to accommodate the base request, as before the wraparound, the wait was effectively done for the reserved_size free space from the start of Ring buffer. In such a case there is a potential of Ring buffer overflow, the instructions at the head of Ring (ACTHD) can get overwritten. Since the base request can fit in the remaining space, there is no need to wraparound immediately. The wraparound will anyway happen later when the reserved part starts getting used. Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> Signed-off-by: Akash Goel <akash.goel@xxxxxxxxx> Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> Link: http://patchwork.freedesktop.org/patch/msgid/1457688402-10411-1-git-send-email-akash.goel@xxxxxxxxx Reviewed-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> (cherry picked from commit 782f6bc0aba037436d6a04d19b23f8b61020a576) Signed-off-by: Jani Nikula <jani.nikula@xxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- drivers/gpu/drm/i915/intel_lrc.c | 6 +++--- drivers/gpu/drm/i915/intel_ringbuffer.c | 6 +++--- 2 files changed, 6 insertions(+), 6 deletions(-) --- a/drivers/gpu/drm/i915/intel_lrc.c +++ b/drivers/gpu/drm/i915/intel_lrc.c @@ -776,11 +776,11 @@ static int logical_ring_prepare(struct d if (unlikely(total_bytes > remain_usable)) { /* * The base request will fit but the reserved space - * falls off the end. So only need to to wait for the - * reserved size after flushing out the remainder. + * falls off the end. So don't need an immediate wrap + * and only need to effectively wait for the reserved + * size space from the start of ringbuffer. */ wait_bytes = remain_actual + ringbuf->reserved_size; - need_wrap = true; } else if (total_bytes > ringbuf->space) { /* No wrapping required, just waiting. */ wait_bytes = total_bytes; --- a/drivers/gpu/drm/i915/intel_ringbuffer.c +++ b/drivers/gpu/drm/i915/intel_ringbuffer.c @@ -2357,11 +2357,11 @@ static int __intel_ring_prepare(struct i if (unlikely(total_bytes > remain_usable)) { /* * The base request will fit but the reserved space - * falls off the end. So only need to to wait for the - * reserved size after flushing out the remainder. + * falls off the end. So don't need an immediate wrap + * and only need to effectively wait for the reserved + * size space from the start of ringbuffer. */ wait_bytes = remain_actual + ringbuf->reserved_size; - need_wrap = true; } else if (total_bytes > ringbuf->space) { /* No wrapping required, just waiting. */ wait_bytes = total_bytes; -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html