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    SubjectRe: [linux-usb-devel] [PATCH] back out sysfs reference count change
    On Tue, Mar 30, 2004 at 06:19:15PM -0800, Andrew Morton wrote:
    >
    > But it looks like that's all in a faraway perfect world, and Greg is going
    > to fix stuff up somehow ;)

    For convenience I will explain the race here..

    cpu 0 cpu 1
    kobject_unregister() sysfs_open_file()
    kobject_del() check_perm()
    sysfs_remove_dir() :
    (dentry remains alive due to ref. taken :
    on the way to sysfs_open_file) :
    kobject_put() :
    kobject_cleanup() kobject_get(->d_fsdata)

    cpu 1 could end up referring to a freed kobject through dentry->d_fsdata or
    starts spitting Badness in kobject_get at lib/kobject.c:429. For triggering
    this race try running these two loops simultaneously on SMP

    # while true; do insmod drivers/net/dummy.ko; rmmod dummy; done
    # while true; do find /sys/class/net | xargs cat; done

    Probably it can be solved by making sure that when sysfs file is
    opened/read/written some _race_ free check is done and fail if kobject if gone.

    Maneesh


    --
    Maneesh Soni
    Linux Technology Center,
    IBM Software Lab, Bangalore, India
    email: maneesh@in.ibm.com
    Phone: 91-80-25044999 Fax: 91-80-25268553
    T/L : 9243696
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