Re: [PATCH 6/7] fcntl: Don't use ambiguous SIG_POLL si_codes

[Eric W. Biederman]

Oleg Nesterov <oleg@xxxxxxxxxx> writes:

> On 07/18, Eric W. Biederman wrote:
>>
>> -			BUG_ON((reason & __SI_MASK) != __SI_POLL);
>> +			BUG_ON((reason < POLL_IN) || (reason > NSIGPOLL));
>                                                       ^^^^^^^^^^^^^^^^^
> looks obviously wrong? Say, POLL_IN is obviously > NSIGPOLL == 6.

Strictly speaking that code is wrong until the next patch
when I remove __SI_POLL.  That is my mistake.

When the values are not their messed up internal kernel variants
the code works fine and makes sense.

#define POLL_IN		1	/* data input available */
#define POLL_OUT	2	/* output buffers available */
#define POLL_MSG	3	/* input message available */
#define POLL_ERR	4	/* i/o error */
#define POLL_PRI	5	/* high priority input available */
#define POLL_HUP	6	/* device disconnected */
#define NSIGPOLL	6

> Probably you meant
>
> 			BUG_ON((reason < POLL_IN) || (reason - POLL_IN > NSIGPOLL)
>
> ?
>
> but this contradicts with the next line:

>>  			if (reason - POLL_IN >= NSIGPOLL)
>>  				si.si_band  = ~0L;
>
> confused...

I am mystified why we test for a condition that we have been bugging on
for ages.

Eric