On 03/22/2012 05:06 AM, Jason Wessel wrote:
> On 03/22/2012 01:30 AM, Dan Carpenter wrote:
>> Hello Tim Bird,
>>
>> This is a semi-automatic email about new static checker warnings.
>>
>> The patch 3492c71d374c: "kdb: Avoid using dbg_io_ops until it is
>> initialized" from Sep 21, 2011, leads to the following Smatch
>> complaint:
>>
>> kernel/debug/kdb/kdb_io.c:746 vkdb_printf()
>> error: we previously assumed 'dbg_io_ops' could be null (see line 692)
>>
>> kernel/debug/kdb/kdb_io.c
>> 691 } else {
>> 692 if (dbg_io_ops && !dbg_io_ops->is_console) {
>> ^^^^^^^^^^
>> New check.
>>
>> 693 len = strlen(kdb_buffer);
>> 694 cp = kdb_buffer;
>> 695 while (len--) {
>> 696 dbg_io_ops->write_char(*cp);
>> 697 cp++;
>> 698 }
>> 699 }
>>
>> [snip]
>>
>> 742
>> 743 kdb_input_flush();
>> 744 c = console_drivers;
>> 745
>> 746 if (!dbg_io_ops->is_console) {
>> ^^^^^^^^^^
>> Old dereference. Should we check here as well?
>
> I had the same question when I reviewed and tested this code. This section
> of code is protected by the kdb pager block, where dbg_io_ops cannot be null.
>
> Should I be adding a comment to that effect, or just pay the price for the
> null check to squelch the warning?
I double-checked this in my code, and was surprised to see that
I already had a null check here. Hmm... There's something wrong
with my patch submission skils, that this didn't get included
in my original patch. :-(
I have to admit that the states that affect this function are somewhat
baffling to me. I hate adding extra code, but it's probably safest to
add the check. We know that during bootup dbg_io_ops spends some time
being null. I would hate to see a future modification to some unrelated state
(e.g. some change to the kdb pager block, which looks completely unrelated),
allow us to hit this problem again in the future.
My vote would be to add the check.
-- Tim
=============================
Tim Bird
Architecture Group Chair, CE Workgroup of the Linux Foundation
Senior Staff Engineer, Sony Network Entertainment
=============================
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