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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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