ALSA: pcm - Fix race with proc files

The PCM proc files may open a race against substream close, which can
end up with an Oops.  Use the open_mutex to protect for it.

Signed-off-by: Takashi Iwai <tiwai@suse.de>

diff --git a/sound/core/pcm.c b/sound/core/pcm.c
index 204af48c5cc17f2f59632bb2089aa03c7b593664..ac242a377aea8068f859bce49aae6825aae5d001 100644 (file)
--- 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