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SubjectRe: [PATCH 12/13] tracing/uprobes: Add more fetch functions
Date
On Thu, 31 Oct 2013 19:22:18 +0100, Oleg Nesterov wrote:
> On 10/29, Namhyung Kim wrote:
>>
>> +static void __user *get_user_vaddr(unsigned long addr, struct trace_uprobe *tu)
>> +{
>> + unsigned long pgoff = addr >> PAGE_SHIFT;
>> + struct vm_area_struct *vma;
>> + struct address_space *mapping;
>> + unsigned long vaddr = 0;
>> +
>> + if (tu == NULL) {
>> + /* A NULL tu means that we already got the vaddr */
>> + return (void __force __user *) addr;
>> + }
>> +
>> + mapping = tu->inode->i_mapping;
>> +
>> + mutex_lock(&mapping->i_mmap_mutex);
>> + vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff, pgoff) {
>> + if (vma->vm_mm != current->mm)
>> + continue;
>> + if (!(vma->vm_flags & VM_READ))
>> + continue;
>> +
>> + vaddr = offset_to_vaddr(vma, addr);
>> + break;
>> + }
>> + mutex_unlock(&mapping->i_mmap_mutex);
>> +
>> + WARN_ON_ONCE(vaddr == 0);
>
> Hmm. But unless I missed something this "addr" passed as an argument can
> be wrong? And if nothing else this or another thread can unmap the vma?

You mean WARN_ON_ONCE here is superfluous? I admit that it should
protect concurrent vma [un]mappings. Please see my reply in other
thread for a new approach.

Thanks,
Namhyung


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