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Subject[RFC patch 1/3] ieee1394: raw1394: replace BKL by local mutex, make ioctl() and mmap() thread-safe
This removes the last usage of the Big Kernel Lock from the ieee1394
stack, i.e. from raw1394's (unlocked_)ioctl and compat_ioctl.

The ioctl()s don't need to take the BKL, but they need to be serialized
per struct file *. In particular, accesses to ->iso_state need to be
serial. We simply use a blocking mutex for this purpose because
libraw1394 does not use O_NONBLOCK. In practice, there is no lock
contention anyway because most if not all libraw1394 clients use a
libraw1394 handle only in a single thread.

mmap() also accesses ->iso_state. Until now this was unprotected
against concurrent changes by ioctls. Fix this bug while we are at it.

Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>
---
drivers/ieee1394/raw1394-private.h | 1 +
drivers/ieee1394/raw1394.c | 23 +++++++++++++++++------
2 files changed, 18 insertions(+), 6 deletions(-)
Index: linux/drivers/ieee1394/raw1394-private.h
===================================================================
--- linux.orig/drivers/ieee1394/raw1394-private.h
+++ linux/drivers/ieee1394/raw1394-private.h
@@ -22,6 +22,7 @@ enum raw1394_iso_state { RAW1394_ISO_INA
struct file_info {
struct list_head list;

+ struct mutex state_mutex;
enum { opened, initialized, connected } state;
unsigned int protocol_version;

Index: linux/drivers/ieee1394/raw1394.c
===================================================================
--- linux.orig/drivers/ieee1394/raw1394.c
+++ linux/drivers/ieee1394/raw1394.c
@@ -34,6 +34,7 @@
#include <linux/fs.h>
#include <linux/poll.h>
#include <linux/module.h>
+#include <linux/mutex.h>
#include <linux/init.h>
#include <linux/interrupt.h>
#include <linux/vmalloc.h>
@@ -2541,11 +2542,18 @@ static int raw1394_read_cycle_timer(stru
static int raw1394_mmap(struct file *file, struct vm_area_struct *vma)
{
struct file_info *fi = file->private_data;
+ int ret;
+
+ mutex_lock(&fi->state_mutex);

if (fi->iso_state == RAW1394_ISO_INACTIVE)
- return -EINVAL;
+ ret = -EINVAL;
+ else
+ ret = dma_region_mmap(&fi->iso_handle->data_buf, file, vma);
+
+ mutex_unlock(&fi->state_mutex);

- return dma_region_mmap(&fi->iso_handle->data_buf, file, vma);
+ return ret;
}

/* ioctl is only used for rawiso operations */
@@ -2659,10 +2667,12 @@ static long do_raw1394_ioctl(struct file
static long raw1394_ioctl(struct file *file, unsigned int cmd,
unsigned long arg)
{
+ struct file_info *fi = file->private_data;
long ret;
- lock_kernel();
+
+ mutex_lock(&fi->state_mutex);
ret = do_raw1394_ioctl(file, cmd, arg);
- unlock_kernel();
+ mutex_unlock(&fi->state_mutex);
return ret;
}

@@ -2724,7 +2734,7 @@ static long raw1394_compat_ioctl(struct
void __user *argp = (void __user *)arg;
long err;

- lock_kernel();
+ mutex_lock(&fi->state_mutex);
switch (cmd) {
/* These requests have same format as long as 'int' has same size. */
case RAW1394_IOC_ISO_RECV_INIT:
@@ -2757,7 +2767,7 @@ static long raw1394_compat_ioctl(struct
err = -EINVAL;
break;
}
- unlock_kernel();
+ mutex_unlock(&fi->state_mutex);

return err;
}
@@ -2791,6 +2801,7 @@ static int raw1394_open(struct inode *in
fi->notification = (u8) RAW1394_NOTIFY_ON; /* busreset notification */

INIT_LIST_HEAD(&fi->list);
+ mutex_init(&fi->state_mutex);
fi->state = opened;
INIT_LIST_HEAD(&fi->req_pending);
INIT_LIST_HEAD(&fi->req_complete);
--
Stefan Richter
-=====-==--- =--- =----
http://arcgraph.de/sr/


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