Messages in this thread Patch in this message | | | Date | Tue, 12 Nov 2013 17:29:51 +0100 | From | Takashi Iwai <> | Subject | Re: [PATCH] ALSA: pcm: retrieve true appl_ptr where stream was unlocked |
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At 12 Nov 2013 16:14:17 +0000, Oskar Schirmer wrote: > > Calculated for data transfer, the local variable appl_ptr is reused, > changed and written back later, though the lock was not held during > the transfer earlier. Admitted, destiny of the lock is not obvious > at all, but this looks much like a race condition candidate, so make > sure to have some original appl_ptr value to work on.
No, appl_ptr doesn't have to be re-read at that point. Otherwise the value will become inconsistent.
This is the write operation to a stream and it's exclusive. The lock is needed to protect the PCM state change (e.g. stopped from an irq handler).
thanks,
Takashi
> > Two occurences. > > Signed-off-by: Oskar Schirmer <oskar@scara.com> > --- > sound/core/pcm_lib.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/sound/core/pcm_lib.c b/sound/core/pcm_lib.c > index 6e03b46..47e836a 100644 > --- a/sound/core/pcm_lib.c > +++ b/sound/core/pcm_lib.c > @@ -2051,6 +2051,7 @@ static snd_pcm_sframes_t snd_pcm_lib_write1(struct snd_pcm_substream *substream, > default: > break; > } > + appl_ptr = runtime->control->appl_ptr; > appl_ptr += frames; > if (appl_ptr >= runtime->boundary) > appl_ptr -= runtime->boundary; > @@ -2283,6 +2284,7 @@ static snd_pcm_sframes_t snd_pcm_lib_read1(struct snd_pcm_substream *substream, > default: > break; > } > + appl_ptr = runtime->control->appl_ptr; > appl_ptr += frames; > if (appl_ptr >= runtime->boundary) > appl_ptr -= runtime->boundary; > -- > 1.7.9.5 >
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