* Oleg Nesterov <o...@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 <o...@redhat.com>
Acked-by: Srikar Dronamraju <sri...@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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