bug#6074: accept-process-output on listening sockets cause non-interruptible infloop

[Pip Cet <pipcet@gmail.com>]

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On Mon, Jul 22, 2019 at 2:26 PM Eli Zaretskii <eliz@gnu.org> wrote:
>
> > From: Pip Cet <pipcet@gmail.com>
> > Date: Mon, 22 Jul 2019 03:52:33 +0000
> >
> > diff --git a/src/process.c b/src/process.c
> > index abadabe77e..1311409274 100644
> > --- a/src/process.c
> > +++ b/src/process.c
> > @@ -5277,7 +5277,9 @@ wait_reading_process_output (intmax_t time_limit, int nsecs, int read_kbd,
> >                 int nread = read_process_output (proc, wait_proc->infd);
> >                 if (nread < 0)
> >                   {
> > -                   if (errno == EIO || would_block (errno))
> > +                   if (errno == EINTR)
> > +                     continue;
> > +                   else
> >                       break;
> >                   }
> >                 else
>
> Isn't it better to simply call rarely_quit inside the loop?

Why would we try again after receiving EINVAL? I believe the right
behavior is to return immediately in this case, just as we do for EIO.

However, we should probably call rarely_quit inside the loop, anyway,
to catch the case of a kernel bug keeping us busy with EINTRs. How's
this?

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From a8991ccc1e846aed9a8f1ba0ebcd2771b623f241 Mon Sep 17 00:00:00 2001
From: Pip Cet <pipcet@gmail.com>
Date: Mon, 22 Jul 2019 03:49:54 +0000
Subject: [PATCH] Don't retry reading after receiving EINVAL (bug#6074)

* src/process.c (wait_reading_process_output): Don't retry reading
from an fd after an unknown error.
---
 src/process.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/src/process.c b/src/process.c
index abadabe77e..9104a392c8 100644
--- a/src/process.c
+++ b/src/process.c
@@ -5270,14 +5270,16 @@ wait_reading_process_output (intmax_t time_limit, int nsecs, int read_kbd,
 	  /* If data can be read from the process, do so until exhausted.  */
 	  if (wait_proc->infd >= 0)
 	    {
+	      unsigned int count = 0;
 	      XSETPROCESS (proc, wait_proc);
 
 	      while (true)
 		{
 		  int nread = read_process_output (proc, wait_proc->infd);
+		  rarely_quit (++count);
 		  if (nread < 0)
 		    {
-		      if (errno == EIO || would_block (errno))
+		      if (errno != EINTR)
 			break;
 		    }
 		  else
-- 
2.22.0