From b406e6103baa3da85950f22d3d46d21a8da654c5 Mon Sep 17 00:00:00 2001 From: Clemens Ladisch Date: Tue, 25 May 2010 09:01:46 +0200 Subject: [PATCH] ALSA: pcm: fix delta calculation at boundary wraparound In the cleanup of the hw_ptr update functions in 2.6.33, the calculation of the delta value was changed to use the modulo operator to protect against a negative difference due to the pointer wrapping around at the boundary. However, the ptr variables are unsigned, so a negative difference would result in the two complement's value which has no relation to the actual difference relative to the boundary; the result is typically some value near LONG_MAX-boundary. Furthermore, even if the modulo operation would be done with signed types, the result of a negative dividend could be negative. The invalid delta value is then caught by the following checks, but this means that the pointer update is ignored. To fix this, use a range check as in the other pointer calculations. Signed-off-by: Clemens Ladisch Cc: Signed-off-by: Takashi Iwai --- sound/core/pcm_lib.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/sound/core/pcm_lib.c b/sound/core/pcm_lib.c index 22aff180dd1f..e9d98be190c5 100644 --- a/sound/core/pcm_lib.c +++ b/sound/core/pcm_lib.c @@ -345,7 +345,9 @@ static int snd_pcm_update_hw_ptr0(struct snd_pcm_substream *substream, new_hw_ptr = hw_base + pos; } __delta: - delta = (new_hw_ptr - old_hw_ptr) % runtime->boundary; + delta = new_hw_ptr - old_hw_ptr; + if (delta < 0) + delta += runtime->boundary; if (xrun_debug(substream, in_interrupt ? XRUN_DEBUG_PERIODUPDATE : XRUN_DEBUG_HWPTRUPDATE)) { char name[16]; -- 2.34.1