Re: [RFC v10][PATCH 09/13] Restore open file descriprtors

[Oren Laadan <orenl@cs.columbia.edu>]

Dave Hansen wrote:
> On Mon, 2008-12-01 at 15:41 -0500, Oren Laadan wrote:
>>>>> +   fd = cr_attach_file(file);      /* no need to cleanup 'file' below */
>>>>> +   if (fd < 0) {
>>>>> +           filp_close(file, NULL);
>>>>> +           ret = fd;
>>>>> +           goto out;
>>>>> +   }
>>>>> +
>>>>> +   /* register new <objref, file> tuple in hash table */
>>>>> +   ret = cr_obj_add_ref(ctx, file, parent, CR_OBJ_FILE, 0);
>>>>> +   if (ret < 0)
>>>>> +           goto out;
>>>> Who said that file still exists at that point?
>> Correct. This call should move higher up befor ethe call to cr_attach_file()
> 
> Is that sufficient?  It seems like we're depending on the fd's reference
> to the 'struct file' to keep it valid in the hash.  If something happens
> to the fd (like the other thread messing with it) the 'struct file' can
> still go away.
> 
> Shouldn't we do another get_file() for the hash's reference?

When a shared object is inserted to the hash we automatically take another
reference to it (according to its type) for as long as it remains in the
hash. See:  'cr_obj_ref_grab()' and 'cr_obj_ref_drop()'.  So by moving that
call higher up, we protect the struct file.

Oren.

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