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authorClemens Ladisch <clemens@ladisch.de>2010-05-25 09:01:46 +0200
committerTakashi Iwai <tiwai@suse.de>2010-05-25 20:23:48 +0200
commitb406e6103baa3da85950f22d3d46d21a8da654c5 (patch)
tree3b989503e6d5c75795980a0387c35fcd82c13ee0
parent57c7ffc9414d79c8ec25800bbdbf8f801b2f148a (diff)
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 <clemens@ladisch.de> Cc: <stable@kernel.org> Signed-off-by: Takashi Iwai <tiwai@suse.de>
-rw-r--r--sound/core/pcm_lib.c4
1 files changed, 3 insertions, 1 deletions
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];