| Date | Mon, 3 Oct 2011 18:29:05 +0200 | From | Oleg Nesterov <> | Subject | Re: [PATCH v5 3.1.0-rc4-tip 5/26] Uprobes: copy of the original instruction. |
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On 09/20, Srikar Dronamraju wrote: > > +static int __copy_insn(struct address_space *mapping, > + struct vm_area_struct *vma, char *insn, > + unsigned long nbytes, unsigned long offset) > +{ > + struct file *filp = vma->vm_file; > + struct page *page; > + void *vaddr; > + unsigned long off1; > + unsigned long idx; > + > + if (!filp) > + return -EINVAL; > + > + idx = (unsigned long) (offset >> PAGE_CACHE_SHIFT); > + off1 = offset &= ~PAGE_MASK; > + > + /* > + * Ensure that the page that has the original instruction is > + * populated and in page-cache. > + */
Hmm. But how we can ensure?
> + page_cache_sync_readahead(mapping, &filp->f_ra, filp, idx, 1);
This schedules the i/o,
> + page = grab_cache_page(mapping, idx);
This finds/locks the page in the page-cache,
> + if (!page) > + return -ENOMEM; > + > + vaddr = kmap_atomic(page); > + memcpy(insn, vaddr + off1, nbytes);
What if this page is not PageUptodate() ?
Somehow this assumes that the i/o was already completed, I don't understand this.
But I am starting to think I simply do not understand this change. To the point, I do not underestand why do we need copy_insn() at all. We are going to replace this page, can't we save/analyze ->insn later when we copy the content of the old page? Most probably I missed something simple...
> +static struct task_struct *get_mm_owner(struct mm_struct *mm) > +{ > + struct task_struct *tsk; > + > + rcu_read_lock(); > + tsk = rcu_dereference(mm->owner); > + if (tsk) > + get_task_struct(tsk); > + rcu_read_unlock(); > + return tsk; > +}
Hmm. Do we really need task_struct?
> -static int install_breakpoint(struct mm_struct *mm, struct uprobe *uprobe) > +static int install_breakpoint(struct mm_struct *mm, struct uprobe *uprobe, > + struct vm_area_struct *vma, loff_t vaddr) > { > - /* Placeholder: Yet to be implemented */ > + struct task_struct *tsk; > + unsigned long addr; > + int ret = -EINVAL; > + > if (!uprobe->consumers) > return 0; > > - atomic_inc(&mm->mm_uprobes_count); > - return 0; > + tsk = get_mm_owner(mm); > + if (!tsk) /* task is probably exiting; bail-out */ > + return -ESRCH; > + > + if (vaddr > TASK_SIZE_OF(tsk)) > + goto put_return;
But this should not be possible, no? How it can map this vaddr above TASK_SIZE ?
get_user_pages(tsk => NULL) is fine. Why else do we need mm->owner ?
Probably used by the next patches... Say, is_32bit_app(tsk). This can use mm->context.ia32_compat (hopefully will be replaced with MMF_COMPAT).
Oleg.
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