On Thu, Jan 12, 2017 at 02:26:42PM -0800, Linus Torvalds wrote: > On Thu, Jan 12, 2017 at 12:26 PM, Alan J. Wylie <a...@wylie.me.uk> wrote: > > > > Strace shows that the processes are hanging in write() and read() calls. > > If this is splice-related, I'm assuming that they aren't actually the > two ends of the same pipe, and there is somebody doing splice in the > middle. > > I'm not seeing that process. I'm assuming it's systemd. Can you try > to find it and strace that one too? Because that middle man is likely > the one that has problems (and is not able to splice from one pipe to > the other). > > Ugh. That one commit has had a lot of bugs in it already. We do not > have good splice test coverage, because almost nobody uses it.
FWIW, I would really like to know what kind of files had been involved. There are two paths that can lead to default_file_splice_read(): splice_direct_to_actor() -> do_splice_to() -> default_file_splice_read() and do_splice() -> do_splice_to() -> default_file_splice_read(). The former only gets there for regular files and block devices. The latter is guaranteed that file is not a pipe. So * not a socket (have ->splice_read() of their own) * not a pipe or FIFO (neither path allows those) * not a block device (have ->splice_read() of their own) * not a regular file on a normal local fs (ditto) So what is it called for in that reproducer?