Messages in this thread | | | Date | Thu, 12 Jan 2017 23:27:19 +0000 | From | Al Viro <> | Subject | Re: 4.9.0 regression in pipe-backed iov_iter with systemd-nspawn |
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On Thu, Jan 12, 2017 at 03:14:41PM -0800, Linus Torvalds wrote: > On Thu, Jan 12, 2017 at 3:02 PM, Linus Torvalds > <torvalds@linux-foundation.org> wrote: > > > > Looking at the callers of "do_splice_to()", we already have the > > wait_for_space() in do_splice(), but we do *not* have it in the > > do_splice_from() case when both the input and output file descriptors > > are pipes. > > Bah. That case doesn't even trigger the new code. I was lazy with my > grep. The two cases are "do_splice()" (which does have the > wait-for-space) and splice_direct_to_actor(). And > splice_direct_to_actor() shouldn't even need it, should it? > > So ignore that. But I think there is something about the EAGAIN.
It might, but I would really like to see where has that EAGAIN come from. I see several possibilities: * wait_for_space() with SPLICE_F_NONBLOCK in flags. Shouldn't happen with 0 in the last argument of splice(2). * default_file_splice_read() seeing pipe->nrbufs == pipe->buffers. Shouldn't be possible after successful wait_for_space(). * vfs_readv() returning -EAGAIN. That might be possible, actually - the damn thing has come from 13761 open("/dev/ptmx", O_RDWR|O_NOCTTY|O_NONBLOCK|O_CLOEXEC) = 5 and O_NONBLOCK had been present in open flags.
What I'd like to see is strace of the same thing on the working kernel, ideally - just prior to the commit bisect has converged to.
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