dash.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Harald van Dijk <harald@gigawatt.nl>
To: Herbert Xu <herbert@gondor.apana.org.au>
Cc: steffen@sdaoden.eu, dash@vger.kernel.org,
	vda.linux@googlemail.com, jilles@stack.nl
Subject: Re: [PATCH] jobs: Block signals during tcsetpgrp
Date: Wed, 6 Jan 2021 21:16:58 +0000	[thread overview]
Message-ID: <cb36ab63-d039-c4ee-c4f3-28bafea56b3a@gigawatt.nl> (raw)
In-Reply-To: <20210106044512.GA28191@gondor.apana.org.au>

On 06/01/2021 04:45, Herbert Xu wrote:
> This patch implements the blocking of SIGTTOU (and everything else)
> while we call tcsetpgrp.
> 
> Reported-by: Steffen Nurpmeso <steffen@sdaoden.eu>
> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
> 
> diff --git a/src/jobs.c b/src/jobs.c
> index 516786f..809f37c 100644
> --- a/src/jobs.c
> +++ b/src/jobs.c
> @@ -1512,7 +1512,13 @@ showpipe(struct job *jp, struct output *out)
>   STATIC void
>   xtcsetpgrp(int fd, pid_t pgrp)
>   {
> -	if (tcsetpgrp(fd, pgrp))
> +	int err;
> +
> +	sigblockall(NULL);
> +	err = tcsetpgrp(fd, pgrp);
> +	sigclearmask();
> +
> +	if (err)
>   		sh_error("Cannot set tty process group (%s)", strerror(errno));
>   }
>   #endif

While this is a step in the right direction, Jilles has already replied 
with an explanation of why this is not enough: if the terminal is in 
TOSTOP mode, it's not just tcsetpgrp() that needs to be handled, it's 
any write as well that may occur while the shell is not in the 
foreground process group. While it may be working according to design 
for messages written when the shell is not supposed to be in the 
foreground process group, it is another story when the shell is both 
responsible for taking itself out of the foreground process group and 
for writing a message. This is made worse by the fact that there is no 
synchronisation with child processes on errors, so even forcibly 
restoring the foreground process group may not be enough: unfortunate 
scheduling may result in a child process immediately setting the 
foreground process group to the child process after the parent process 
attempted to restore it to itself. I have not yet seen a good solution 
for this.

Cheers,
Harald van Dijk

  reply	other threads:[~2021-01-06 21:17 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-12-19 17:28 dash 0.5.11.2, busybox sh 1.32.0, FreeBSD 12.2 sh: spring TTOU but should not i think Steffen Nurpmeso
2020-12-19 22:21 ` Steffen Nurpmeso
2020-12-19 23:52   ` Harald van Dijk
2020-12-21 16:24     ` Jilles Tjoelker
2020-12-21 19:43       ` Steffen Nurpmeso
2020-12-23 20:18       ` Harald van Dijk
2020-12-24 15:29         ` Jilles Tjoelker
2021-01-10 23:56         ` Harald van Dijk
2021-01-06  4:46       ` Herbert Xu
2021-01-06  4:45     ` [PATCH] jobs: Block signals during tcsetpgrp Herbert Xu
2021-01-06 21:16       ` Harald van Dijk [this message]
2021-01-06 22:41         ` Jilles Tjoelker
2021-01-07  7:36         ` Denys Vlasenko

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=cb36ab63-d039-c4ee-c4f3-28bafea56b3a@gigawatt.nl \
    --to=harald@gigawatt.nl \
    --cc=dash@vger.kernel.org \
    --cc=herbert@gondor.apana.org.au \
    --cc=jilles@stack.nl \
    --cc=steffen@sdaoden.eu \
    --cc=vda.linux@googlemail.com \
    --subject='Re: [PATCH] jobs: Block signals during tcsetpgrp' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).