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    SubjectRe: [PATCH 2/7] revoke: add f_light flag for struct file
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    On Friday 09 March 2007 11:43, Pekka Enberg wrote:
    > On 3/9/07, Eric Dumazet <dada1@cosmosbay.com> wrote:
    > > Cannot we use a flag in 'struct files_struct', set to one when the task
    > > is mono-thread (at task creation in fact), and set to 0 when it creates a
    > > new thread (or when someone remotely access to this "struct
    > > files_struct" in /proc/pid/fd/... )
    >
    > How does that work? fget_light() has a built-in assumption that as
    > long as you don't share files_struct, it's okay not to take an extra
    > reference as current is only one doing close(2) and revoke(2) changes
    > that. So it's not really about being single-threaded or not.

    I just dropped one (silly ?) idea and expected you made the hard work :)

    Then just drop the fget_light() 'optimisation' and always take a reference
    (atomic on f_count) regardless of single-thread or not. Instead of dirtying
    f_light, just do the straightforward thing and be with it.

    (that is : fget_light() = fget() = no more keeping fput_needed everywhere, and
    convoluted things in some dark sides of the kernel.

    It will save some conditional branches and complexity, and you dont need this
    f_light thing.

    >
    > On 3/9/07, Eric Dumazet <dada1@cosmosbay.com> wrote:
    > > Also, the thing is racy.
    >
    > Aah, fget_light() indeed has a race window between fcheck_files() and
    > set_f_light().

    Yes, you see how hard it is to get this right.
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