Messages in this thread | | | From | Måns Rullgård <> | Subject | Re: [PATCH v2] n_tty: Fix read_buf race condition, increment read_head after pushing data | Date | Wed, 12 Nov 2014 11:53:59 +0000 |
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Christian Riesch <christian.riesch@omicron.at> writes:
> On Tue, Nov 11, 2014 at 2:04 PM, Måns Rullgård <mans@mansr.com> wrote: >> Christian Riesch <christian.riesch@omicron.at> writes: > [...]>> diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c >>> index 2e900a9..b09f326 100644 >>> --- a/drivers/tty/n_tty.c >>> +++ b/drivers/tty/n_tty.c >>> @@ -321,7 +321,9 @@ static void n_tty_check_unthrottle(struct tty_struct *tty) >>> >>> static inline void put_tty_queue(unsigned char c, struct n_tty_data *ldata) >>> { >>> - *read_buf_addr(ldata, ldata->read_head++) = c; >>> + *read_buf_addr(ldata, ldata->read_head) = c; >>> + /* increment read_head _after_ placing the character in the buffer */ >>> + ldata->read_head++; >>> } >> >> Is that comment really necessary? > > No, I am pretty sure that removing the comment would not break the code ;-) > > I just thought it would be good to have some kind of reminder here. > Otherwise someone may think: Hey, it would be a good idea to do the > increment right in the first line. And submit a patch for it.
The intent all along was to increment after the write. Nobody needs reminding of that. The problem was a misunderstanding of when the post-increment takes effect. As much as we'd like for everybody to have a thorough knowledge of C, a random tty driver doesn't seem the place to educate them.
-- Måns Rullgård mans@mansr.com -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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