Re: [PATCH 2/3] uprobes: introduce MMF_RECALC_UPROBES

[Srikar Dronamraju <srikar@linux.vnet.ibm.com>]

* Oleg Nesterov <oleg@redhat.com> [2012-08-19 18:40:40]:

> Add the new MMF_RECALC_UPROBES flag, it means that MMF_HAS_UPROBES
> can be false positive after remove_breakpoint() or uprobe_munmap().
> It is also set by uprobe_dup_mmap(), this is not optimal but simple.
> We could add the new hook, uprobe_dup_vma(), to set MMF_HAS_UPROBES
> only if the new mm actually has uprobes, but I don't think this
> makes sense.
> 
> The next patch will use this flag to clear MMF_HAS_UPROBES.
> 
> Signed-off-by: Oleg Nesterov <oleg@redhat.com>

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

> ---
>  include/linux/sched.h   |    3 ++-
>  kernel/events/uprobes.c |   39 +++++++++++++++++++++++++++++++++++----
>  2 files changed, 37 insertions(+), 5 deletions(-)
> 
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index c0fcfb7..d6899b0 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -441,7 +441,8 @@ extern int get_dumpable(struct mm_struct *mm);
>  #define MMF_VM_HUGEPAGE		17	/* set when VM_HUGEPAGE is set on vma */
>  #define MMF_EXE_FILE_CHANGED	18	/* see prctl_set_mm_exe_file() */
> 
> -#define MMF_HAS_UPROBES		19	/* might have uprobes */
> +#define MMF_HAS_UPROBES		19	/* has uprobes */
> +#define MMF_RECALC_UPROBES	20	/* MMF_HAS_UPROBES can be wrong */
> 
>  #define MMF_INIT_MASK		(MMF_DUMPABLE_MASK | MMF_DUMP_FILTER_MASK)
> 
> diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> index abe077e..176de8c 100644
> --- a/kernel/events/uprobes.c
> +++ b/kernel/events/uprobes.c
> @@ -686,7 +686,9 @@ install_breakpoint(struct uprobe *uprobe, struct mm_struct *mm,
>  		set_bit(MMF_HAS_UPROBES, &mm->flags);
> 
>  	ret = set_swbp(&uprobe->arch, mm, vaddr);
> -	if (ret && first_uprobe)
> +	if (!ret)
> +		clear_bit(MMF_RECALC_UPROBES, &mm->flags);
> +	else if (first_uprobe)
>  		clear_bit(MMF_HAS_UPROBES, &mm->flags);
> 
>  	return ret;
> @@ -695,6 +697,11 @@ install_breakpoint(struct uprobe *uprobe, struct mm_struct *mm,
>  static void
>  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;
> +
> +	set_bit(MMF_RECALC_UPROBES, &mm->flags);
>  	set_orig_insn(&uprobe->arch, mm, vaddr);
>  }
> 
> @@ -1027,6 +1034,25 @@ int uprobe_mmap(struct vm_area_struct *vma)
>  	return 0;
>  }
> 
> +static bool
> +vma_has_uprobes(struct vm_area_struct *vma, unsigned long start, unsigned long end)
> +{
> +	loff_t min, max;
> +	struct inode *inode;
> +	struct rb_node *n;
> +
> +	inode = vma->vm_file->f_mapping->host;
> +
> +	min = vaddr_to_offset(vma, start);
> +	max = min + (end - start) - 1;
> +
> +	spin_lock(&uprobes_treelock);
> +	n = find_node_in_range(inode, min, max);
> +	spin_unlock(&uprobes_treelock);
> +
> +	return !!n;
> +}
> +
>  /*
>   * Called in context of a munmap of a vma.
>   */
> @@ -1038,10 +1064,12 @@ void uprobe_munmap(struct vm_area_struct *vma, unsigned long start, unsigned lon
>  	if (!atomic_read(&vma->vm_mm->mm_users)) /* called by mmput() ? */
>  		return;
> 
> -	if (!test_bit(MMF_HAS_UPROBES, &vma->vm_mm->flags))
> +	if (!test_bit(MMF_HAS_UPROBES, &vma->vm_mm->flags) ||
> +	     test_bit(MMF_RECALC_UPROBES, &vma->vm_mm->flags))
>  		return;
> 
> -	/* TODO: unmapping uprobe(s) will need more work */
> +	if (vma_has_uprobes(vma, start, end))
> +		set_bit(MMF_RECALC_UPROBES, &vma->vm_mm->flags);
>  }
> 
>  /* Slot allocation for XOL */
> @@ -1147,8 +1175,11 @@ void uprobe_dup_mmap(struct mm_struct *oldmm, struct mm_struct *newmm)
>  {
>  	newmm->uprobes_state.xol_area = NULL;
> 
> -	if (test_bit(MMF_HAS_UPROBES, &oldmm->flags))
> +	if (test_bit(MMF_HAS_UPROBES, &oldmm->flags)) {
>  		set_bit(MMF_HAS_UPROBES, &newmm->flags);
> +		/* unconditionally, dup_mmap() skips VM_DONTCOPY vmas */
> +		set_bit(MMF_RECALC_UPROBES, &newmm->flags);
> +	}
>  }
> 
>  /*
> -- 
> 1.5.5.1
>