From: Jeff King <peff@peff.net>
Date: Wed, 19 Dec 2018 23:22:00 GMT
Subject: Re: Periodic hang during git index-pack
Message-ID: <20181219232200.GB21283@sigill.intra.peff.net>
In-Reply-To: <CALjAwxiB1uDfg4iPFjh2dNibEZa5mJ0RwhCzt0R2b87NTVqWfA@mail.gmail.com>

On Wed, Dec 19, 2018 at 10:59:30PM +0000, Sitsofe Wheeler wrote:

> While using trying to use git to clone a remote repository git
> index-pack occasionally goes on to hang:
> [...]
> Looking at where it is stuck, git is doing read of a pipe:
> 
> #0  0x00007fd1b845034e in __libc_read (fd=fd@entry=0,
> buf=buf@entry=0x55ab81e19d40 <input_buffer>, nbytes=nbytes@entry=4096)
>     at ../sysdeps/unix/sysv/linux/read.c:27
> #1  0x000055ab81b51b23 in read (__nbytes=4096, __buf=0x55ab81e19d40
> <input_buffer>, __fd=0)
>     at /usr/include/x86_64-linux-gnu/bits/unistd.h:44

Index-pack is reading the pack on stdin, so it's expecting more bytes.
Those bytes should be coming from the git-clone process, which is
relaying the bytes from the other side.

Check the backtrace of git-clone to see why it isn't feeding more data
(but note that it will generally have two threads -- one processing the
data from the remote, and one wait()ing for index-pack to finish).

My guess, though, is that you'll find that git-clone is simply waiting
on another pipe: the one from ssh.

-Peff