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Date: Thu, 9 Aug 2012 19:02:51 +0530
From: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To: Oleg Nesterov <oleg@...hat.com>
Cc: Ingo Molnar <mingo@...e.hu>, Peter Zijlstra <peterz@...radead.org>,
Ananth N Mavinakayanahalli <ananth@...ibm.com>,
Anton Arapov <anton@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/7] uprobes: introduce MMF_HAS_UPROBES
* Oleg Nesterov <oleg@...hat.com> [2012-08-08 19:37:47]:
> Add the new MMF_HAS_UPROBES flag. It is set by install_breakpoint()
> and it is copied by dup_mmap(), uprobe_pre_sstep_notifier() checks
> it to avoid the slow path if the task was never probed. Perhaps it
> makes sense to check it in valid_vma(is_register => false) as well.
>
> This needs the new dup_mmap()->uprobe_dup_mmap() hook. We can't use
> uprobe_reset_state() or put MMF_HAS_UPROBES into MMF_INIT_MASK, we
> need oldmm->mmap_sem to avoid the race with uprobe_register() or
> mmap() from another thread.
>
> Currently we never clear this bit, it can be false-positive after
> uprobe_unregister() or uprobe_munmap() or if dup_mmap() hits the
> probed VM_DONTCOPY vma. But this is fine correctness-wise and has
> no effect unless the task hits the non-uprobe breakpoint.
>
In which case, cant we just delete uprobe_munmap() altogether.
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>
> ---
> include/linux/sched.h | 2 ++
> include/linux/uprobes.h | 5 +++++
> kernel/events/uprobes.c | 22 +++++++++++++++++++++-
> kernel/fork.c | 1 +
> 4 files changed, 29 insertions(+), 1 deletions(-)
>
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index cbf3a71..c0fcfb7 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -441,6 +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_INIT_MASK (MMF_DUMPABLE_MASK | MMF_DUMP_FILTER_MASK)
>
> struct sighand_struct {
> diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h
> index 03ae547..4a37ab1 100644
> --- a/include/linux/uprobes.h
> +++ b/include/linux/uprobes.h
> @@ -108,6 +108,7 @@ extern int uprobe_register(struct inode *inode, loff_t offset, struct uprobe_con
> extern void uprobe_unregister(struct inode *inode, loff_t offset, struct uprobe_consumer *uc);
> extern int uprobe_mmap(struct vm_area_struct *vma);
> extern void uprobe_munmap(struct vm_area_struct *vma, unsigned long start, unsigned long end);
> +extern void uprobe_dup_mmap(struct mm_struct *oldmm, struct mm_struct *newmm);
> extern void uprobe_free_utask(struct task_struct *t);
> extern void uprobe_copy_process(struct task_struct *t);
> extern unsigned long __weak uprobe_get_swbp_addr(struct pt_regs *regs);
> @@ -138,6 +139,10 @@ static inline void
> uprobe_munmap(struct vm_area_struct *vma, unsigned long start, unsigned long end)
> {
> }
> +static inline void
> +uprobe_dup_mmap(struct mm_struct *oldmm, struct mm_struct *newmm)
> +{
> +}
> static inline void uprobe_notify_resume(struct pt_regs *regs)
> {
> }
> diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> index 309309e..2a42319 100644
> --- a/kernel/events/uprobes.c
> +++ b/kernel/events/uprobes.c
> @@ -649,6 +649,7 @@ static int
> install_breakpoint(struct uprobe *uprobe, struct mm_struct *mm,
> struct vm_area_struct *vma, unsigned long vaddr)
> {
> + bool first_uprobe;
> int ret;
>
> /*
> @@ -680,7 +681,17 @@ install_breakpoint(struct uprobe *uprobe, struct mm_struct *mm,
> uprobe->flags |= UPROBE_COPY_INSN;
> }
>
> + /*
> + * set MMF_HAS_UPROBES in advance for uprobe_pre_sstep_notifier(),
> + * the task can hit this breakpoint right after __replace_page().
> + */
> + first_uprobe = !test_bit(MMF_HAS_UPROBES, &mm->flags);
> + if (first_uprobe)
> + set_bit(MMF_HAS_UPROBES, &mm->flags);
> +
> ret = set_swbp(&uprobe->arch, mm, vaddr);
> + if (ret && first_uprobe)
> + clear_bit(MMF_HAS_UPROBES, &mm->flags);
>
> return ret;
> }
> @@ -1034,6 +1045,9 @@ 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))
> + return;
> +
I am not sure whats the purpose of the above test
> /* TODO: unmapping uprobe(s) will need more work */
and I am unable to think what more we would want to do here.
> }
>
> @@ -1144,6 +1158,12 @@ void uprobe_reset_state(struct mm_struct *mm)
> mm->uprobes_state.xol_area = NULL;
> }
>
> +void uprobe_dup_mmap(struct mm_struct *oldmm, struct mm_struct *newmm)
> +{
> + if (test_bit(MMF_HAS_UPROBES, &oldmm->flags))
> + set_bit(MMF_HAS_UPROBES, &newmm->flags);
> +}
> +
> /*
> * - search for a free slot.
> */
> @@ -1511,7 +1531,7 @@ int uprobe_pre_sstep_notifier(struct pt_regs *regs)
> {
> struct uprobe_task *utask;
>
> - if (!current->mm)
> + if (!current->mm || !test_bit(MMF_HAS_UPROBES, ¤t->mm->flags))
> return 0;
>
> utask = current->utask;
> diff --git a/kernel/fork.c b/kernel/fork.c
> index 0e419ab..ab970c3 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -350,6 +350,7 @@ static int dup_mmap(struct mm_struct *mm, struct mm_struct *oldmm)
>
> down_write(&oldmm->mmap_sem);
> flush_cache_dup_mm(oldmm);
> + uprobe_dup_mmap(oldmm, mm);
> /*
> * Not linked in yet - no deadlock potential:
> */
> --
> 1.5.5.1
>
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