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    SubjectRe: [PATCH][RFC] Linux VM hooks for advanced RDMA NICs
    > @@ -267,6 +270,11 @@
    >
    > unsigned long hiwater_rss; /* High-water RSS usage */
    > unsigned long hiwater_vm; /* High-water virtual memory usage */
    > +
    > +#ifdef CONFIG_IOPROC
    > + /* hooks for io devices with advanced RDMA capabilities */
    > + struct ioproc_ops *ioproc_ops;
    > +#endif
    > };

    > +int
    > +ioproc_register_ops(struct mm_struct *mm, struct ioproc_ops *ip)
    > +{
    > + ip->next = mm->ioproc_ops;
    > + mm->ioproc_ops = ip;
    > +
    > + return 0;
    > +}
    > +
    > +EXPORT_SYMBOL_GPL(ioproc_register_ops);
    > +
    > +int
    > +ioproc_unregister_ops(struct mm_struct *mm, struct ioproc_ops *ip)
    > +{
    > + struct ioproc_ops **tmp;
    > +
    > + for (tmp = &mm->ioproc_ops; *tmp && *tmp != ip; tmp= &(*tmp)->next)
    > + ;
    > + if (*tmp) {
    > + *tmp = ip->next;
    > + return 0;
    > + }
    > +
    > + return -EINVAL;
    > +}
    > +
    > +EXPORT_SYMBOL_GPL(ioproc_unregister_ops);

    You don't seem to use any synchronization mechanism to protect the
    ioproc list from concurrent modifications, right ?
    I understand that it might be useless as long as QsNet is the only user
    of ioprocs and takes care of locking the address space somewhere in the
    driver before adding/removing hooks.
    But, if this patch is to be merged to the mainline, you probably need
    to do something here. It's not clear how other in-kernel users
    (IB, Myri, Ammasso, ...) might use ioprocs.
    And actually, I think all ioproc list traversal need to be protected
    as well.

    A spinlock_t ioproc_lock is probably appropriate here.
    I don't know whether any of the existing locks in the task_struct
    might be used instead.

    Regards,
    Brice
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