[PATCH] proper lseek locking in ALSA, take 3

[PATCH] proper lseek locking in ALSA, take 3

[Robert Love]

The attached patch implements proper locking in ALSA lseek methods. 
Note ALSA has 3 lseek implementations, but only:

	sound/core/info.c :: snd_info_entry_llseek()

requires locking.  I wrapped the function in the BKL.  According to
Jaroslav Kysela the gus_mem_proc method is only called from above.  The
third lseek, in hwdep.c, clearly doesn't need locking.  Without this
patch, the above lseek is not safe.

Patch is against 2.5.5, please apply.

	Robert Love	

diff -urN linux-2.5.5/sound/core/info.c linux/sound/core/info.c
--- linux-2.5.5/sound/core/info.c	Tue Feb 19 21:11:01 2002
+++ linux/sound/core/info.c	Tue Feb 19 21:50:18 2002
@@ -29,6 +29,7 @@
 #include <sound/info.h>
 #include <sound/version.h>
 #include <linux/proc_fs.h>
+#include <linux/smp_lock.h>
 #ifdef CONFIG_DEVFS_FS
 #include <linux/devfs_fs_kernel.h>
 #endif
@@ -162,31 +163,40 @@
 {
 	snd_info_private_data_t *data;
 	struct snd_info_entry *entry;
+	int ret = -EINVAL;
 
 	data = snd_magic_cast(snd_info_private_data_t, file->private_data, return -ENXIO);
 	entry = data->entry;
+	lock_kernel();
 	switch (entry->content) {
 	case SNDRV_INFO_CONTENT_TEXT:
 		switch (orig) {
 		case 0:	/* SEEK_SET */
 			file->f_pos = offset;
-			return file->f_pos;
+			ret = file->f_pos;
+			goto out;
 		case 1:	/* SEEK_CUR */
 			file->f_pos += offset;
-			return file->f_pos;
+			ret = file->f_pos;
+			goto out;
 		case 2:	/* SEEK_END */
 		default:
-			return -EINVAL;
+			goto out;
 		}
 		break;
 	case SNDRV_INFO_CONTENT_DATA:
-		if (entry->c.ops->llseek)
-			return entry->c.ops->llseek(entry,
+		if (entry->c.ops->llseek) {
+			ret = entry->c.ops->llseek(entry,
 						    data->file_private_data,
 						    file, offset, orig);
+			goto out;
+		}
 		break;
 	}
-	return -ENXIO;
+	ret = -ENXIO;
+out:
+	unlock_kernel();
+	return ret;
 }
 
 static ssize_t snd_info_entry_read(struct file *file, char *buffer,

Re: [PATCH] proper lseek locking in ALSA, take 3

[Jaroslav Kysela]

On 20 Feb 2002, Robert Love wrote:

> The attached patch implements proper locking in ALSA lseek methods.
> Note ALSA has 3 lseek implementations, but only:
>
> 	sound/core/info.c :: snd_info_entry_llseek()
>
> requires locking.  I wrapped the function in the BKL.  According to
> Jaroslav Kysela the gus_mem_proc method is only called from above.  The
> third lseek, in hwdep.c, clearly doesn't need locking.  Without this
> patch, the above lseek is not safe.
>
> Patch is against 2.5.5, please apply.

We have this patch already in our ALSA CVS tree, so it will be commited to
Linus in next patch round. Thanks.

						Jaroslav

-----
Jaroslav Kysela <perex@suse.cz>
Linux Kernel Sound Maintainer
ALSA Project  http://www.alsa-project.org
SuSE Linux    http://www.suse.com