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    SubjectRe: 2.6.27-rc7-sha1: EIP at proc_sys_compare+0x36/0x50
    Linus Torvalds <torvalds@linux-foundation.org> writes:

    > I actually like my second patch better - it looks simpler, and it means
    > that the rules for filesystems using d_compare() are a bit clearer: at
    > least we'll only pass them dentries to look at that haven't gone through
    > d_drop (and we do hold dentry->d_lock that serializes all of that).
    >
    > So here it is again (I sent it out just minutes ago, but you weren't on
    > that cc, you must have picked this up off the kernel list)
    >
    > NOTE! Totally untested patch! It looks sane and really obvious, but maybe
    > it has some insane and non-obvious bug.

    We definitely have a race between d_kill setting dentry->d_inode = NULL
    and proc_sys_compare reading d_inode.

    We don't generate negative dentries for /proc/sys.

    In dput atomic_dec_and_lock takes the lock before setting the count to 0.
    So there is no race there.

    Testing for d_unhashed and getting us out of rcu limbo before calling
    into the filesystem methods makes the reasoning a lot clearer.


    Looks good to me.

    Reviewed-by: "Eric W. Biederman" <ebiederm@xmission.com>



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