linux-kernel - Re: [PATCH v4] tools: jobserver: Prevent deadlock caused by incorrect jobserver configuration and enhance error reporting

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Message-ID: <20260112175221.2d59c161@foz.lan>
Date: Mon, 12 Jan 2026 17:52:21 +0100
From: Mauro Carvalho Chehab <mchehab+huawei@...nel.org>
To: Jonathan Corbet <corbet@....net>
Cc: Changbin Du <changbin.du@...wei.com>, Mauro Carvalho Chehab
 <mchehab@...nel.org>, linux-doc@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4] tools: jobserver: Prevent deadlock caused by
 incorrect jobserver configuration and enhance error reporting

Em Mon, 12 Jan 2026 09:23:30 -0700
Jonathan Corbet <corbet@....net> escreveu:

> Jonathan Corbet <corbet@....net> writes:
> 
> > The warning comes from JobserverExec::open(), for an exception that
> > appears to be expected.  This is the sort of use of exceptions that has
> > made me almost swear off them entirely in Python - it's a huge try block
> > that is using exceptions to hide a bunch of the assumptions and logic.
> > I'll be posting a patch shortly to remove this non-exceptional exception
> > case.  
> 
> Here's a first step, just to show what I have in mind.
> 
> jon
> 
> From bdbb48e153714ae1c9e5214ba3ecd6142536ee6f Mon Sep 17 00:00:00 2001
> From: Jonathan Corbet <corbet@....net>
> Date: Mon, 12 Jan 2026 09:19:49 -0700
> Subject: [PATCH] jobserver: Begin to split up the big try: block
> 
> The parsing of jobserver options is done in a massive try: block that hides
> problems and (perhaps) bugs.  Start to split up that block and make the
> logic explicit by moving the initial parsing of MAKEFLAGS out of that
> block.

Agreed. Still, I would try to minimize the number of try/except, as those
makes the code more complex to read. 

FYI, when I converted it to a class in a way that it could
be re-used by doc build, I opted, by purpose, to preserve the code
as much as possible, to be bug-compatible with the original version,
but yeah, this big try/except would work better if split.

> Among other things, this removes the warning:
> 
>   jobserver: warning: IndexError('list index out of range')
> 
> Seen after the application of bbf8c67aa6ae8.
> 
> Signed-off-by: Jonathan Corbet <corbet@....net>
> ---
>  tools/lib/python/jobserver.py | 28 ++++++++++++++++++++--------
>  1 file changed, 20 insertions(+), 8 deletions(-)
> 
> diff --git a/tools/lib/python/jobserver.py b/tools/lib/python/jobserver.py
> index 616411087725e..c674319f6cb1f 100755
> --- a/tools/lib/python/jobserver.py
> +++ b/tools/lib/python/jobserver.py
> @@ -58,15 +58,27 @@ class JobserverExec:
>  
>          if self.is_open:
>              return
> -
> +        self.claim = None
> +        self.is_open = True  # We only try once
> +        #
> +        # See what they have told us to do here.
> +        #
> +        try:
> +            flags = os.environ['MAKEFLAGS']
> +        except KeyError:
> +            return

I would use, instead:

	flags = os.environ.get('MAKEFLAGS', '')

No need to have a return there...

> +        #
> +        # Look for "--jobserver=R,W"
> +        # Note that GNU Make has used --jobserver-fds and --jobserver-auth
> +        # so this handles all of them.
> +        #
> +        opts = [x for x in flags.split(" ") if x.startswith("--jobserver")]
> +        if not opts:
> +            return

... as, if MAKEFLAGS is an empty string, opts will be an empty list, causing
it to return.

> +        #
> +        # OK, parse the result.
> +        #
>          try:
> -            # Fetch the make environment options.
> -            flags = os.environ["MAKEFLAGS"]
> -            # Look for "--jobserver=R,W"
> -            # Note that GNU Make has used --jobserver-fds and --jobserver-auth
> -            # so this handles all of them.
> -            opts = [x for x in flags.split(" ") if x.startswith("--jobserver")]
> -
>              # Parse out R,W file descriptor numbers and set them nonblocking.
>              # If the MAKEFLAGS variable contains multiple instances of the
>              # --jobserver-auth= option, the last one is relevant.



Thanks,
Mauro