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    SubjectRe: [PATCH] remove BKL from drivers' release functions
    "David C. Hansen" wrote:
    >
    > Russell King wrote:
    >
    > >On Wed, Nov 28, 2001 at 03:32:32PM -0800, David C. Hansen wrote:
    > >
    > >>Nothing, because the BKL is not held for all opens anymore. In most of
    > >>the cases that we addressed, the BKL was in release _only_, not in open
    > >>at all. There were quite a few drivers where we added a spinlock, or
    > >>used atomic operations to keep open from racing with release.
    > >>
    > >
    > >All char and block devs are opened with the BKL held - see chrdev_open in
    > >fs/devices.c and do_open in fs/block_dev.c
    > >
    > I wrote a quick and dirty char device driver to see if this happened.
    > If I run two tasks doing a bunch of opens and closes, the -EBUSY
    > condition in the open function does happen. Is my driver doing
    > something wrong?
    >
    > Here is the meat of the driver:
    >
    > static int Device_Open = 0;
    >
    > int testdev_open(struct inode *inode, struct file *file)
    > {
    > if ( test_and_set_bit(0,&Device_Open) ) {
    > printk( "attempt to open testdev more than once\n" );
    > return -EBUSY;
    > }
    > MOD_INC_USE_COUNT;
    > return SUCCESS;
    > }
    >
    > int testdev_release(struct inode *inode, struct file *file)
    > {
    > clear_bit(0,&Device_Open);
    > MOD_DEC_USE_COUNT;
    > return 0;
    > }

    it is still racy, that's why struct file_operations and other structs
    have an 'owner' member......

    --
    Jeff Garzik | Only so many songs can be sung
    Building 1024 | with two lips, two lungs, and one tongue.
    MandrakeSoft | - nomeansno

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