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SubjectRe: [PATCH 2/3] uprobes: introduce MMF_RECALC_UPROBES
* 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
>



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