From: Junio C Hamano <gitster@pobox.com>
To: Jeff King <peff@peff.net>
Cc: git@vger.kernel.org, Johannes Schindelin <Johannes.Schindelin@gmx.de>
Subject: Re: [RFC/PATCH] pipe_command(): mark stdin descriptor as non-blocking
Date: Tue, 02 Aug 2022 08:04:39 -0700 [thread overview]
Message-ID: <xmqqbkt2k7p4.fsf@gitster.g> (raw)
In-Reply-To: <YuikU//9OrdpKQcE@coredump.intra.peff.net> (Jeff King's message of "Tue, 2 Aug 2022 00:13:07 -0400")
Jeff King <peff@peff.net> writes:
> Our pipe_command() helper lets you both write to and read from a child
> process on its stdin/stdout. It's supposed to work without deadlocks
> because we use poll() to check when descriptors are ready for reading or
> writing. But there's a bug: if both the data to be written and the data
> to be read back exceed the pipe buffer, we'll deadlock.
> ...
> If you set add.interactive.useBuiltin to false, the problem goes away,
> because now we're not using pipe_command() anymore (instead, that part
> happens in perl). But this isn't a bug in the interactive code at all.
> It's the underlying pipe_command() code which is broken, and has been
> all along.
> ...
> The obvious fix is to put the descriptor into non-blocking mode, and
> indeed, that makes the problem go away. Callers shouldn't need to
> care, because they never see the descriptor (they hand us a buffer to
> feed into it).
Thanks for a very well reasoned and explained patch.
> - more importantly, I'm not sure of the portability implications of
> the fix. This is our first use of O_NONBLOCK outside of the
> compat/simple-ipc unix-socket code. Do we need to abstract this
> behind a compat/ layer for Windows?
Yup. A very good question to ask for the platform maintainer.
> run-command.c | 17 +++++++++++++++++
> 1 file changed, 17 insertions(+)
>
> diff --git a/run-command.c b/run-command.c
> index 14f17830f5..45bffb4b11 100644
> --- a/run-command.c
> +++ b/run-command.c
> @@ -1418,6 +1418,14 @@ static int pump_io(struct io_pump *slots, int nr)
> return 0;
> }
>
> +static int make_nonblock(int fd)
> +{
> + int flags = fcntl(fd, F_GETFL);
> + if (flags < 0)
> + return -1;
> + flags |= O_NONBLOCK;
> + return fcntl(fd, F_SETFL, flags);
> +}
>
> int pipe_command(struct child_process *cmd,
> const char *in, size_t in_len,
> @@ -1438,6 +1446,15 @@ int pipe_command(struct child_process *cmd,
> return -1;
>
> if (in) {
> + if (make_nonblock(cmd->in) < 0) {
> + error_errno("unable to make pipe non-blocking");
> + close(cmd->in);
> + if (out)
> + close(cmd->out);
> + if (err)
> + close(cmd->err);
> + return -1;
> + }
> io[nr].fd = cmd->in;
> io[nr].type = POLLOUT;
> io[nr].u.out.buf = in;
next prev parent reply other threads:[~2022-08-02 15:04 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-02 4:13 [RFC/PATCH] pipe_command(): mark stdin descriptor as non-blocking Jeff King
2022-08-02 15:04 ` Junio C Hamano [this message]
2022-08-02 15:39 ` Jeff King
2022-08-02 16:16 ` Junio C Hamano
2022-08-03 3:53 ` [PATCH v2] " Jeff King
2022-08-03 16:45 ` René Scharfe
2022-08-03 17:20 ` Jeff King
2022-08-03 21:56 ` René Scharfe
2022-08-05 15:36 ` Jeff King
2022-08-05 21:13 ` René Scharfe
2022-08-07 10:15 ` René Scharfe
2022-08-07 17:41 ` Jeff King
2022-08-10 5:39 ` René Scharfe
2022-08-10 19:53 ` Jeff King
2022-08-10 22:35 ` René Scharfe
2022-08-11 8:52 ` Jeff King
2022-08-10 5:39 ` [PATCH] mingw: handle writes to non-blocking pipe René Scharfe
2022-08-10 9:07 ` Johannes Schindelin
2022-08-10 20:02 ` Jeff King
2022-08-10 22:34 ` René Scharfe
2022-08-11 8:47 ` Jeff King
2022-08-11 17:35 ` René Scharfe
2022-08-11 18:20 ` Jeff King
2022-08-14 15:37 ` René Scharfe
2022-08-17 5:39 ` Jeff King
2022-08-17 6:04 ` [PATCH v2 0/6] fix pipe_command() deadlock Jeff King
2022-08-17 6:04 ` [PATCH v2 1/6] compat: add function to enable nonblocking pipes Jeff King
2022-08-17 20:23 ` Junio C Hamano
2022-08-18 5:41 ` Jeff King
2022-08-17 6:05 ` [PATCH v2 2/6] nonblock: support Windows Jeff King
2022-08-17 6:06 ` [PATCH v2 3/6] git-compat-util: make MAX_IO_SIZE define globally available Jeff King
2022-08-17 6:08 ` [PATCH v2 4/6] pipe_command(): avoid xwrite() for writing to pipe Jeff King
2022-08-17 6:09 ` [PATCH v2 5/6] pipe_command(): handle ENOSPC when writing to a pipe Jeff King
2022-08-17 18:57 ` Junio C Hamano
2022-08-18 5:38 ` Jeff King
2022-08-17 6:10 ` [PATCH v2 6/6] pipe_command(): mark stdin descriptor as non-blocking Jeff King
2022-08-17 6:20 ` [PATCH v2 0/6] fix pipe_command() deadlock Jeff King
2022-08-19 21:19 ` René Scharfe
2022-08-20 7:04 ` Jeff King
2022-08-07 10:14 ` [PATCH v2] pipe_command(): mark stdin descriptor as non-blocking René Scharfe
2022-08-08 12:55 ` Johannes Schindelin
2022-08-08 12:59 ` Johannes Schindelin
2022-08-09 13:04 ` Jeff King
2022-08-09 22:10 ` Johannes Schindelin
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