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    SubjectRe: [PATCH 5/7] uprobes: Introduce filter_chain()
    * Oleg Nesterov <oleg@redhat.com> [2012-11-23 21:28:12]:

    > Add the new helper filter_chain(). Currently it is only placeholder,
    > the comment explains what is should do. We will change it later to
    > consult every consumer to decide whether we need to install the swbp.
    > Until then it works as if any consumer returns true, this matches the
    > current behavior.
    >
    > Change install_breakpoint() to call filter_chain() instead of checking
    > uprobe->consumers != NULL. We obviously need this, and this equally
    > closes the race with _unregister().
    >
    > Change remove_breakpoint() to call this helper too. Currently this is
    > pointless because remove_breakpoint() is only called when the last
    > consumer goes away, but we will change this.
    >
    > Signed-off-by: Oleg Nesterov <oleg@redhat.com>

    Acked-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>

    > ---
    > kernel/events/uprobes.c | 24 +++++++++++++++++++-----
    > 1 files changed, 19 insertions(+), 5 deletions(-)
    >
    > diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
    > index e761974..edc47ae 100644
    > --- a/kernel/events/uprobes.c
    > +++ b/kernel/events/uprobes.c
    > @@ -614,6 +614,18 @@ static int prepare_uprobe(struct uprobe *uprobe, struct file *file,
    > return ret;
    > }
    >
    > +static bool filter_chain(struct uprobe *uprobe)
    > +{
    > + /*
    > + * TODO:
    > + * for_each_consumer(uc)
    > + * if (uc->filter(...))
    > + * return true;
    > + * return false;
    > + */
    > + return uprobe->consumers != NULL;
    > +}
    > +
    > static int
    > install_breakpoint(struct uprobe *uprobe, struct mm_struct *mm,
    > struct vm_area_struct *vma, unsigned long vaddr)
    > @@ -624,11 +636,10 @@ install_breakpoint(struct uprobe *uprobe, struct mm_struct *mm,
    > /*
    > * If probe is being deleted, unregister thread could be done with
    > * the vma-rmap-walk through. Adding a probe now can be fatal since
    > - * nobody will be able to cleanup. Also we could be from fork or
    > - * mremap path, where the probe might have already been inserted.
    > - * Hence behave as if probe already existed.
    > + * nobody will be able to cleanup. But in this case filter_chain()
    > + * must return false, all consumers have gone away.
    > */
    > - if (!uprobe->consumers)
    > + if (!filter_chain(uprobe))
    > return 0;
    >
    > ret = prepare_uprobe(uprobe, vma->vm_file, mm, vaddr);
    > @@ -655,10 +666,12 @@ install_breakpoint(struct uprobe *uprobe, struct mm_struct *mm,
    > static int
    > remove_breakpoint(struct uprobe *uprobe, struct mm_struct *mm, unsigned long vaddr)
    > {
    > - /* can happen if uprobe_register() fails */
    > if (!test_bit(MMF_HAS_UPROBES, &mm->flags))
    > return 0;
    >
    > + if (filter_chain(uprobe))
    > + return 0;
    > +
    > set_bit(MMF_RECALC_UPROBES, &mm->flags);
    > return set_orig_insn(&uprobe->arch, mm, vaddr);
    > }
    > @@ -1382,6 +1395,7 @@ static void mmf_recalc_uprobes(struct mm_struct *mm)
    > * This is not strictly accurate, we can race with
    > * uprobe_unregister() and see the already removed
    > * uprobe if delete_uprobe() was not yet called.
    > + * Or this uprobe can be filtered out.
    > */
    > if (vma_has_uprobes(vma, vma->vm_start, vma->vm_end))
    > return;
    > --
    > 1.5.5.1
    >



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