On Sun, Jun 26, 2016 at 11:21:11PM +0000, Eric Wong wrote:
> We should continue to loop after EAGAIN/EWOULDBLOCK as the
> intent of xread is to read as much as possible until an
> EOF or real error occurs.
>
> Fixes: 1079c4be0b720 ("xread: poll on non blocking fds")
>
> Signed-off-by: Eric Wong <e@xxxxxxxxx>
> ---
> wrapper.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/wrapper.c b/wrapper.c
> index 5dc4e15..f1155d0 100644
> --- a/wrapper.c
> +++ b/wrapper.c
> @@ -255,6 +255,7 @@ ssize_t xread(int fd, void *buf, size_t len)
> * call to read(2).
> */
> poll(&pfd, 1, -1);
> + continue;
> }
> }
> return nr;
Eek. This is a real bug that could cause racy and apparently random
failures. I guess we haven't seen many reports of it because it only
triggers when you have unexpected non-blocking descriptors, which are
not all that common. But your fix is definitely the right thing to do.
I also wondered how we managed to miss such an obvious point in review
of the original patch. Sadly, we _did_ notice it[1] but it looks like we
never fixed the problem. That is even more disturbing.
-Peff
[1] http://mid.gmane.org/20151218031336.GA8467@xxxxxxxxxxxxxxxxxxxxx
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