[alsa-devel] EBADFD caused by commit dec428c352217010e4b8bd750d302b8062339d32

[Takashi Iwai]

On Mon, 11 Apr 2016 17:08:01 +0200,
Lars Lindqvist wrote:
> 
> On 2016-04-11 Takashi Iwai wrote:
> > [Added Qing Cai to Cc, who was the author of the patch in question]
> > 
> > On Sun, 10 Apr 2016 23:57:11 +0200,
> > Lars Lindqvist wrote:
> > > 
> > > Hi!
> > > 
> > > Since alsa-lib commit  dec428c352217010e4b8bd750d302b8062339d32, I've
> > > occationally been hit by an EBADFD whenever any program tries to play
> > > sound.  The  situation  I get is  that the  first shmget succeds,  so
> > > dmix->shmid >= 0, therefore first_instance = 0.
> > 
> > I wonder how does this succeed?  It's a leftover shmem?
> > But then why it contains the garbage...?
> 
> I seem to be able to trigger it by having one client open, starting another,
> and quickly closing the first one.

One possible case is that the second stream is opened almost at the
same time as the first stream, and the second stream reaches to the
point checking SND_PCM_DIRECT_MAGIC before the first one finishes the
initialization.  Does a hackish patch like below make any difference?


Takashi

---
diff --git a/src/pcm/pcm_direct.c b/src/pcm/pcm_direct.c
index 14de734d98eb..d0aa4258004f 100644
--- a/src/pcm/pcm_direct.c
+++ b/src/pcm/pcm_direct.c
@@ -92,6 +92,7 @@ int snd_pcm_direct_shm_create_or_connect(snd_pcm_direct_t *dmix)
 {
 	struct shmid_ds buf;
 	int tmpid, err, first_instance = 0;
+	int repeat = 0;
 	
 retryget:
 	dmix->shmid = shmget(dmix->ipc_key, sizeof(snd_pcm_direct_share_t),
@@ -136,6 +137,9 @@ retryget:
 	} else {
 		if (dmix->shmptr->magic != SND_PCM_DIRECT_MAGIC) {
 			snd_pcm_direct_shm_discard(dmix);
+			/* might be racy, let's retry for a few times */
+			if (++repeat < 10)
+				goto retryget;
 			return -EINVAL;
 		}
 	}