[024/200] ALSA: pcm: fix delta calculation at boundary wraparound
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From: Greg KH on 1 Jul 2010 18:10 2.6.34-stable review patch. If anyone has any objections, please let me know. ------------------ From: Clemens Ladisch <clemens(a)ladisch.de> commit b406e6103baa3da85950f22d3d46d21a8da654c5 upstream. 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(a)ladisch.de> Signed-off-by: Takashi Iwai <tiwai(a)suse.de> Signed-off-by: Greg Kroah-Hartman <gregkh(a)suse.de> --- sound/core/pcm_lib.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) --- a/sound/core/pcm_lib.c +++ b/sound/core/pcm_lib.c @@ -345,7 +345,9 @@ static int snd_pcm_update_hw_ptr0(struct 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]; -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |