[alsa-devel] 1.1.4 bug report: dmix fails when using both 32-bit and 64-bit clients

[Takashi Iwai]

On Thu, 25 May 2017 18:51:10 +0200,
Cheng Sun wrote:
> 
> On 25 May 2017 at 17:31, Takashi Iwai <tiwai at suse.de> wrote:
> > On Thu, 25 May 2017 17:43:44 +0200,
> > Cheng Sun wrote:
> >>
> >> On 25 May 2017 14:49, "Takashi Iwai" <tiwai at suse.de> wrote:
> >> >
> >> > On Wed, 24 May 2017 21:13:46 +0200,
> >> > Cheng Sun wrote:
> >> > >
> >> > > Hi all,
> >> > >
> >> > > The following commit (released in v1.1.4) introduced an issue where a
> >> > > client compiled against a 32-bit (x86) compile of alsa-lib cannot use
> >> > > the same dmix as a client compiled against a 64-bit alsa-lib.
> >> > >
> >> > >     1a9bd0f0448106b917ae7f7bedccfcbf6ce84802
> >> > >
> >> > > The error message is:
> >> > >
> >> > >     ALSA lib pcm_dmix.c:1077:(snd_pcm_dmix_open) unable to create IPC
> >> > > shm instance
> >> > >
> >> > > The following forum post (not mine) describes the symptoms of the
> >> > > issue in more detail (although the git commit the poster specified is
> >> > > not correct):
> >> > >
> >> > >
> >> https://forums.gentoo.org/viewtopic-p-8072290.html?sid=c2fbca45102933ddf9ca7cf8b6713e56
> >> >
> >> > There is a known problem when you mix up two alsa-lib versions because
> >> > of the changes in dmix shmem struct.  The solution should upgrade all
> >> > users.
> >>
> >> (Apologies for duplicate email --accidentally sent the first reply to the
> >> wrong address.)
> >>
> >> Arch Linux has upgraded both its 32 and 64 bit packages to v1.1.4, and I'm
> >> still experiencing this problem.
> >>
> >> While bisecting the bug I linked against two compiles of the same alsa-lib
> >> versions each time.
> >>
> >> Let me know if I can provide any other information.
> >
> > OK, at first to see whether it's the issue of the struct size
> > mismatch, check the following patch.  If it is, you'll see the error
> > message.  To be sure, check both cases: 64bit -> 32bit, and 32bit ->
> > 64bit.
> 
> The behaviour is different for the two cases.
> 
> 1) If 64bit client is started first, then the 32bit client prints the following:
> 
> magic mismatch: shmptr=a15ad4f0, expected=a15ad4ec
> ALSA lib pcm_dmix.c:1077:(snd_pcm_dmix_open) unable to create IPC shm instance
> 
> 2) If 32bit client is started first, then the 64bit client only prints:
> 
> ALSA lib pcm_dmix.c:1077:(snd_pcm_dmix_open) unable to create IPC shm instance
> 
> I've added some further print statements and it turns out that this is
> because the "return err;" on line 115 is triggered.

Hm, so at least the struct size difference is a problem.
Doese the patch below change the behavior?


Takashi

---
diff --git a/src/pcm/pcm_direct.h b/src/pcm/pcm_direct.h
--- a/src/pcm/pcm_direct.h
+++ b/src/pcm/pcm_direct.h
@@ -66,7 +66,6 @@ typedef struct {
 	char socket_name[256];			/* name of communication socket */
 	snd_pcm_type_t type;			/* PCM type (currently only hw) */
 	int use_server;
-	unsigned int recoveries;		/* no of executed recoveries on slave*/
 	struct {
 		unsigned int format;
 		snd_interval_t rate;
@@ -113,6 +112,7 @@ typedef struct {
 			unsigned long long chn_mask;
 		} dshare;
 	} u;
+	unsigned int recoveries;		/* no of executed recoveries on slave*/
 } snd_pcm_direct_share_t;
 
 typedef struct snd_pcm_direct snd_pcm_direct_t;