kernel/alsa-fix-substream-proc-status-read.patch

From: Takashi Iwai <tiwai@suse.de>
To: Chuck Ebbert <cebbert@redhat.com>
Cc: alsa-devel@alsa-project.org, linux-kernel@vger.kernel.org
Subject: Re: [alsa-devel] 2.6.36-rc2-git5: Oops in	snd_pcm_substream_proc_status_read()
Date: Thu, 02 Sep 2010 10:31:11 +0200

At Wed, 1 Sep 2010 04:19:24 -0400,
Chuck Ebbert wrote:
> 
> 
>  https://bugzilla.redhat.com/show_bug.cgi?id=628404
> 
> general protection fault: 0000 [#1] SMP 
> last sysfs file:
> /sys/devices/pci0000:00/0000:00:1b.0/sound/card0/pcmC0D0c/pcm_class
> CPU 1 
> Modules linked in: vfat fat fuse ebtable_nat ebtables ipt_MASQUERADE
> iptable_nat nf_nat bridge stp llc sunrpc cpufreq_ondemand acpi_cpufreq
> freq_table mperf ip6t_REJECT nf_conntrack_ipv6 xt_physdev ip6table_filter
> ip6_tables kvm_intel kvm uinput snd_hda_codec_conexant usblp arc4 ecb
> snd_hda_intel snd_hda_codec snd_hwdep snd_seq snd_seq_device iwlagn snd_pcm
> iwlcore thinkpad_acpi snd_timer snd i2c_i801 mac80211 soundcore microcode
> iTCO_wdt iTCO_vendor_support e1000e cfg80211 wmi snd_page_alloc rfkill ipv6
> usb_storage i915 drm_kms_helper drm i2c_algo_bit i2c_core video output [last
> unloaded: scsi_wait_scan]
> 
> Pid: 16071, comm: pulseaudio Not tainted 2.6.36-0.11.rc2.git5.fc15.x86_64 #1
> 74585FU/74585FU
> RIP: 0010:[<ffffffffa0296742>]  [<ffffffffa0296742>]
> snd_pcm_substream_proc_status_read+0x164/0x1ad [snd_pcm]
> RSP: 0018:ffff8801178c1b58  EFLAGS: 00010292
> RAX: 6b6b6b6b6b6b6b6b RBX: ffff88003d993bc8 RCX: 0000000000000000
> RDX: ffffffffa02a1996 RSI: ffffffffa02a1997 RDI: ffff88003d993bc8
> RBP: ffff8801178c1c18 R08: 0000000000000006 R09: 00000000fffffff7
> R10: ffff8800044ea048 R11: 0000000000000000 R12: ffff8801332d31b0
> R13: ffff88013438d488 R14: ffff88013438e050 R15: ffff880111131880
> FS:  00007fbccba77780(0000) GS:ffff880002e00000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
> CR2: 00007fbf324db008 CR3: 00000001157be000 CR4: 00000000000006e0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
> Process pulseaudio (pid: 16071, threadinfo ffff8801178c0000, task
> ffff880130f88000)
> Stack:
>  0000000000000003 0000000000005e84 000000002ee6c142 0000000000005e85  
> <0> 000000001624774a 0000000000000000 00000000000064b0 00000000000064b0
> <0> 00000000000064b0 00000000000064b0 0000000000000000 0000000000000000  
> Call Trace:  
>  [<ffffffffa020ac22>] snd_info_entry_open+0x307/0x389 [snd]
>  [<ffffffff81179034>] proc_reg_open+0xfa/0x17a
>  [<ffffffffa020a91b>] ? snd_info_entry_open+0x0/0x389 [snd]
>  [<ffffffffa0209fa7>] ? snd_info_entry_release+0x0/0xd8 [snd]
>  [<ffffffff81178f3a>] ? proc_reg_open+0x0/0x17a
>  [<ffffffff81128f1f>] __dentry_open+0x1c2/0x338
>  [<ffffffff81129da0>] nameidata_to_filp+0x3f/0x50
>  [<ffffffff81136200>] do_last+0x432/0x5af
>  [<ffffffff81246a75>] ? __raw_spin_lock_init+0x31/0x50
>  [<ffffffff811365ad>] do_filp_open+0x230/0x5e1
>  [<ffffffff810fac10>] ? might_fault+0x5c/0xac
>  [<ffffffff8114040b>] ? alloc_fd+0x3b/0x17c
>  [<ffffffff8107fc2a>] ? lock_release+0x19a/0x1a6
>  [<ffffffff8114053a>] ? alloc_fd+0x16a/0x17c
>  [<ffffffff81129e11>] do_sys_open+0x60/0xfc
>  [<ffffffff8149aca2>] ? trace_hardirqs_on_thunk+0x3a/0x3f
>  [<ffffffff81129ecd>] sys_open+0x20/0x22
>  [<ffffffff81009cb2>] system_call_fastpath+0x16/0x1b  
> Code: df 31 c0 e8 e6 40 f7 ff 48 c7 c6 90 19 2a a0 48 89 df 31 c0 e8 d5 40 f7
> ff 49 8b 84 24 f0 00 00 00 48 c7 c6 97 19 2a a0 48 89 df <48> 8b 50 08 31 c0 e8
> b8 40 f7 ff 49 8b 84 24 f8 00 00 00 48 c7 
> RIP  [<ffffffffa0296742>] snd_pcm_substream_proc_status_read+0x164/0x1ad
> [snd_pcm]
>  RSP <ffff8801178c1b58>
> ---[ end trace 96389f116dd90473 ]---
> 
> Faulting insn:
> 48 8b 50 08           mov    0x8(%rax),%rdx
> 
> RAX: 6b6b6b6b6b6b6b6b
> 
> sound/core/pcm.c:453:
> 
>    snd_iprintf(buffer, "hw_ptr : %ld\n", runtime->status->hw_ptr);
> 
> runtime = 0x6b6b6b6b6b6b6b6b
> 
> The code checks for NULL before using it, but this is a poison value.  

Looks like a race.
Could you check whether the patch below fixes the problem?


thanks,

Takashi

---
diff --git a/sound/core/pcm.c b/sound/core/pcm.c
index 204af48..ac242a3 100644
--- a/sound/core/pcm.c
+++ b/sound/core/pcm.c
@@ -372,14 +372,17 @@ static void snd_pcm_substream_proc_hw_params_read(struct snd_info_entry *entry,
 						  struct snd_info_buffer *buffer)
 {
 	struct snd_pcm_substream *substream = entry->private_data;
-	struct snd_pcm_runtime *runtime = substream->runtime;
+	struct snd_pcm_runtime *runtime;
+
+	mutex_lock(&substream->pcm->open_mutex);
+	runtime = substream->runtime;
 	if (!runtime) {
 		snd_iprintf(buffer, "closed\n");
-		return;
+		goto unlock;
 	}
 	if (runtime->status->state == SNDRV_PCM_STATE_OPEN) {
 		snd_iprintf(buffer, "no setup\n");
-		return;
+		goto unlock;
 	}
 	snd_iprintf(buffer, "access: %s\n", snd_pcm_access_name(runtime->access));
 	snd_iprintf(buffer, "format: %s\n", snd_pcm_format_name(runtime->format));
@@ -398,20 +401,25 @@ static void snd_pcm_substream_proc_hw_params_read(struct snd_info_entry *entry,
 		snd_iprintf(buffer, "OSS period frames: %lu\n", (unsigned long)runtime->oss.period_frames);
 	}
 #endif
+ unlock:
+	mutex_unlock(&substream->pcm->open_mutex);
 }
 
 static void snd_pcm_substream_proc_sw_params_read(struct snd_info_entry *entry,
 						  struct snd_info_buffer *buffer)
 {
 	struct snd_pcm_substream *substream = entry->private_data;
-	struct snd_pcm_runtime *runtime = substream->runtime;
+	struct snd_pcm_runtime *runtime;
+
+	mutex_lock(&substream->pcm->open_mutex);
+	runtime = substream->runtime;
 	if (!runtime) {
 		snd_iprintf(buffer, "closed\n");
-		return;
+		goto unlock;
 	}
 	if (runtime->status->state == SNDRV_PCM_STATE_OPEN) {
 		snd_iprintf(buffer, "no setup\n");
-		return;
+		goto unlock;
 	}
 	snd_iprintf(buffer, "tstamp_mode: %s\n", snd_pcm_tstamp_mode_name(runtime->tstamp_mode));
 	snd_iprintf(buffer, "period_step: %u\n", runtime->period_step);
@@ -421,24 +429,29 @@ static void snd_pcm_substream_proc_sw_params_read(struct snd_info_entry *entry,
 	snd_iprintf(buffer, "silence_threshold: %lu\n", runtime->silence_threshold);
 	snd_iprintf(buffer, "silence_size: %lu\n", runtime->silence_size);
 	snd_iprintf(buffer, "boundary: %lu\n", runtime->boundary);
+ unlock:
+	mutex_unlock(&substream->pcm->open_mutex);
 }
 
 static void snd_pcm_substream_proc_status_read(struct snd_info_entry *entry,
 					       struct snd_info_buffer *buffer)
 {
 	struct snd_pcm_substream *substream = entry->private_data;
-	struct snd_pcm_runtime *runtime = substream->runtime;
+	struct snd_pcm_runtime *runtime;
 	struct snd_pcm_status status;
 	int err;
+
+	mutex_lock(&substream->pcm->open_mutex);
+	runtime = substream->runtime;
 	if (!runtime) {
 		snd_iprintf(buffer, "closed\n");
-		return;
+		goto unlock;
 	}
 	memset(&status, 0, sizeof(status));
 	err = snd_pcm_status(substream, &status);
 	if (err < 0) {
 		snd_iprintf(buffer, "error %d\n", err);
-		return;
+		goto unlock;
 	}
 	snd_iprintf(buffer, "state: %s\n", snd_pcm_state_name(status.state));
 	snd_iprintf(buffer, "owner_pid   : %d\n", pid_vnr(substream->pid));
@@ -452,6 +465,8 @@ static void snd_pcm_substream_proc_status_read(struct snd_info_entry *entry,
 	snd_iprintf(buffer, "-----\n");
 	snd_iprintf(buffer, "hw_ptr      : %ld\n", runtime->status->hw_ptr);
 	snd_iprintf(buffer, "appl_ptr    : %ld\n", runtime->control->appl_ptr);
+ unlock:
+	mutex_unlock(&substream->pcm->open_mutex);
 }
 
 #ifdef CONFIG_SND_PCM_XRUN_DEBUG