Re: [PATCH] mac80211: use BUG_ON and return -EINVAL if rate_lowest_index() fails

["Arend van Spriel" <arend@broadcom.com>]

On 06/17/2011 12:08 AM, Pavel Roskin wrote:
> On 06/16/2011 06:22 AM, Stanislaw Gruszka wrote:
>> Hi Pavel
>>
>> On Wed, Jun 15, 2011 at 06:02:52PM -0400, Pavel Roskin wrote:
>>> WARN_ON is not enough, as we cannot return a valid index, and the
>>> callers will use whatever we return, causing a cascade of oopses and
>>> eventually a panic.
>> We have fedora bug (https://bugzilla.redhat.com/show_bug.cgi?id=702627)
>> where only that warning is generated, and system works further (at least
>> bug reporter did not mention about it's hang). When moving to BUG(),
>> system from user perspective will simply hang, what is much worse.
>> I think, we should rather fix callers to be prepared and recover itself
>> when rate_lowest_index fail. Of course fixing real bug(s) that cause
>> rate index is not found would be best.
> In my case, I was able to restart the system by sysrq when using BUG_ON,
> but the system would hang hard with WARN_ON.  I think continuing after
> returning an invalid index is wrong.  It will lead to memory corruption
> that could in turn lead to corruption of the filesystem.

I think it is generally a bad idea to use BUG_ON as a solution. As 
Stanislaw indicated there are platforms which can continue without a 
hang so you are regressing those. Regarding your patch I think the 
-EINVAL is good to have, but leave the WARN_ON.

Gr. AvS

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