ALSA: pcm: fix infinite loop in snd_pcm_update_hw_ptr0()
authorKelly Anderson <kelly@silka.with-linux.com>
Fri, 1 Apr 2011 09:58:25 +0000 (11:58 +0200)
committerTakashi Iwai <tiwai@suse.de>
Fri, 1 Apr 2011 16:01:23 +0000 (18:01 +0200)
commit12ff414e2e4512f59fe191dc18e856e2939a1c79
tree7aa36c6a9f80f749cd36251c8e2c31990cef3270
parent840126579da56edae8ecc4a0d85198f742982f10
ALSA: pcm: fix infinite loop in snd_pcm_update_hw_ptr0()

When period interrupts are disabled, snd_pcm_update_hw_ptr0() compares
the current time against the time estimated for the current hardware
pointer to detect xruns.  The somewhat fuzzy threshold in the while loop
makes it possible that hdelta becomes negative; the comparison being
done with unsigned types then makes the loop go through the entire 263
negative range, and, depending on the value, never reach an unsigned
value that is small enough to stop the loop.  Doing this with interrupts
disabled results in the machine locking up.

To prevent this, ensure that the loop condition uses signed types for
both operands so that the comparison is correctly done.

Many thanks to Kelly Anderson for debugging this.

Reported-by: Nix <nix@esperi.org.uk>
Reported-by: "Christopher K." <c.krooss@googlemail.com>
Reported-and-tested-by: Kelly Anderson <kelly@silka.with-linux.com>
Signed-off-by: Kelly Anderson <kelly@silka.with-linux.com>
[cl: remove unneeded casts; use a temp variable]
Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
Cc: 2.6.38 <stable@kernel.org>

Signed-off-by: Takashi Iwai <tiwai@suse.de>
sound/core/pcm_lib.c