linux-kernel - [3.18.3] poll() on gpio pins broken

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-ID: <20150129145636.GU21469@belle.intranet.vanheusden.com>
Date:	Thu, 29 Jan 2015 15:56:36 +0100
From:	folkert <folkert@...heusden.com>
To:	linux-kernel@...r.kernel.org
Subject: [3.18.3] poll() on gpio pins broken

Hi,

For timekeeping I wrote a program which waits for interrupts on
gpio-pins and then tells the local ntp daemon the clock offset.
I'm aware of the pps support in recent kernel but that does not work
(yet) on all platforms (eg cubieboard 1).

This has worked for quite some time but no longer.

Until at least kernel 3.12 I could do:

// export gpio pin
// set direction to in
// set direction to rising
int fd = open("/sys.../value", O_RDONLY);
fdset[0].fd = fd;
fdset[0].events = POLLPRI;
fdset[0].revents = 0;
poll(fdset, 1, -1);
// at this point pin went high

So: I would setup a gpio-pin using /sys-files, and then use poll() to
wait for the interrupt triggered by the level of the gpio pin going
high.
This worked fine on all raspberry pi's I tried, a nanos g20, a beagle
bone black and a cubieboard 1.

Since kernel 3.18.3 (.4 as well) this no longer works: 

1422542104.894908947] interrupt #2459, offset -0.105091s
1422542104.895162937] interrupt #2460, offset -0.104837s
1422542104.895408928] interrupt #2461, offset -0.104591s
1422542104.895650919] interrupt #2462, offset -0.104349s
1422542104.896293896] interrupt #2463, offset -0.103706s
...

As you can see suddenly the poll returns immediately.

strace learns me:
poll([{fd=3, events=POLLPRI}], 1, -1)   = 1 ([{fd=3, revents=POLLPRI|POLLERR}])

So apparently somewhere between 3.12 and 3.18 it is no longer
allowed/possible to do poll() on a gpio-pin value device.

Am I right that something broke the abi? Or have I been doing it wrong
and did that became visible?
Please advise.

thanks

Folkert van Heusden

-- 
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/