linux-kernel - Re: [PATCH RFC 1/3] fs: introduce helper d_path

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Sat, 8 May 2021 08:30:43 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Jia He <justin.he@....com>
Cc:     Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Jonathan Corbet <corbet@....net>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Al Viro <viro@....linux.org.uk>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        "Eric W . Biederman" <ebiederm@...ssion.com>,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Ira Weiny <ira.weiny@...el.com>,
        Eric Biggers <ebiggers@...gle.com>,
        "Ahmed S. Darwish" <a.darwish@...utronix.de>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-s390 <linux-s390@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH RFC 1/3] fs: introduce helper d_path_fast()

On Sat, May 8, 2021 at 5:29 AM Jia He <justin.he@....com> wrote:
>
> This helper is similar to d_path except for not taking seqlock/spinlock.

I see why you did it that way, but conditional locking is something we
really really try to avoid in the kernel.

It basically makes a lot of static tools unable to follow the locking
rules, and it makes it hard for people to se what's going on too.

So instead of passing a "bool need_lock" thing down, the way to do
these things is generally to extract the code inside the locked region
into a helper function of its own, and then you have

  __unlocked_version(...)
  {
       .. do the actual work
  }

  locked_version(..)
  {
      take_lock(..)
      retval = __unlocked_version(..);
      release_lock(..);
      return retval;
  }

this prepend_path() case is a bit more complicated because there's two
layers of locking, but I think the pattern should still work fine.

In fact, I think it would clean up prepend_path() and make it more
legible to have the two layers of mount_lock / rename_lock be done in
callers with the restarting being done as a loop in the caller rather
than as "goto restart_*".

              Linus