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

Oleg Nesterov [off-list ref] writes:

On 07/18, Eric W. Biederman wrote:

quoted

-			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:

quoted

 			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