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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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