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authorKelly Anderson <kelly@silka.with-linux.com>2011-04-01 11:58:25 +0200
committerTakashi Iwai <tiwai@suse.de>2011-04-01 18:01:23 +0200
commit12ff414e2e4512f59fe191dc18e856e2939a1c79 (patch)
tree7aa36c6a9f80f749cd36251c8e2c31990cef3270 /sound
parent840126579da56edae8ecc4a0d85198f742982f10 (diff)
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>
Diffstat (limited to 'sound')
-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 a82e3756a72d..64449cb8f873 100644
--- a/sound/core/pcm_lib.c
+++ b/sound/core/pcm_lib.c
@@ -375,6 +375,7 @@ static int snd_pcm_update_hw_ptr0(struct snd_pcm_substream *substream,
}
if (runtime->no_period_wakeup) {
+ snd_pcm_sframes_t xrun_threshold;
/*
* Without regular period interrupts, we have to check
* the elapsed time to detect xruns.
@@ -383,7 +384,8 @@ static int snd_pcm_update_hw_ptr0(struct snd_pcm_substream *substream,
if (jdelta < runtime->hw_ptr_buffer_jiffies / 2)
goto no_delta_check;
hdelta = jdelta - delta * HZ / runtime->rate;
- while (hdelta > runtime->hw_ptr_buffer_jiffies / 2 + 1) {
+ xrun_threshold = runtime->hw_ptr_buffer_jiffies / 2 + 1;
+ while (hdelta > xrun_threshold) {
delta += runtime->buffer_size;
hw_base += runtime->buffer_size;
if (hw_base >= runtime->boundary)

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