On Friday 04 December 2015 06:38:25 Al Viro wrote:
> On cross-builds the __poll_t annotations had caught something interesting:
> void spufs_mfc_callback(struct spu *spu)
> {
> ....
> mask = 0;
> if (free_elements & 0xffff)
> mask |= POLLOUT;
> if (tagstatus & ctx->tagwait)
> mask |= POLLIN;
>
> kill_fasync(&ctx->mfc_fasync, SIGIO, mask);
> ....
> }
>
> That's arch/powerpc/platforms/cell/spufs/file.c. WTF is kill_fasync()
> getting as the last argument here? Valid values are
> #define POLL_IN (__SI_POLL|1) /* data input available */
> #define POLL_OUT (__SI_POLL|2) /* output buffers available */
> #define POLL_MSG (__SI_POLL|3) /* input message available */
> #define POLL_ERR (__SI_POLL|4) /* i/o error */
> #define POLL_PRI (__SI_POLL|5) /* high priority input available */
> #define POLL_HUP (__SI_POLL|6) /* device disconnected */
>
> Use of POLLIN, POLLOUT, etc. here is wrong - kill_fasync() will step into
> BUG_ON((reason & __SI_MASK) != __SI_POLL);
> in send_sigio_to_task(). Other two callers of kill_fasync() in that file
> are trivially fixed by switching to POLL_IN and POLL_OUT; with this one
> I've no idea what had been intended.
>
> What's more, I really wonder if it had _ever_ been tested - these
> kill_fasync()
> calls had been introduced in
> commit 8b3d6663c6217e4f50cc3720935a96da9b984117
> Author: Arnd Bergmann <a...@arndb.de>
> Date: Tue Nov 15 15:53:52 2005 -0500
>
> [PATCH] spufs: cooperative scheduler support
> more than 5 years after that BUG_ON() had been added - it goes back to
> + /* Make sure we are called with one of the POLL_*
> + reasons, otherwise we could leak kernel stack into
> + userspace. */
> + if ((reason & __SI_MASK) != __SI_POLL)
> + BUG();
> in 2.3.99pre-10-3, on May 25 2000.
>
> What the hell am I missing here? Has that code been DOA and never used by
> anyone in all the decade it had been in mainline?
I don't remember why we put in fasync support, but I have checked the libspe
implementation and found that it doesn't use it (not a big surprise there).
It always uses epoll() to get notifications from spufs, and based on your
explanation I assume everything else (there may have been one or two users
that used the low-level interfaces rather than libspe) did too.
Arnd
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