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  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:   Thu, 6 Jun 2019 21:38:24 +0800
From:   Herbert Xu <>
To:     "Paul E. McKenney" <>
Cc:     Alan Stern <>,
        Boqun Feng <>,
        Linus Torvalds <>,
        Frederic Weisbecker <>,
        Fengguang Wu <>, LKP <>,
        LKML <>,
        Netdev <>,
        "David S. Miller" <>,
        Andrea Parri <>,
        Luc Maranget <>,
        Jade Alglave <>
Subject: Re: rcu_read_lock lost its compiler barrier

On Thu, Jun 06, 2019 at 03:58:17AM -0700, Paul E. McKenney wrote:
> I cannot immediately think of a way that the compiler could get this
> wrong even in theory, but similar code sequences can be messed up.
> The reason for this is that in theory, the compiler could use the
> stored-to location as temporary storage, like this:
> 	a = whatever;	// Compiler uses "a" as a temporary
> 	do_something();
> 	whatever = a;
> 	a = 1;		// Intended store

Well if the compiler is going to do this then surely it would
continue to do this even if you used WRITE_ONCE.  Remember a is
not volatile, only the access of a through WRITE_ONCE is volatile.

Email: Herbert Xu <>
Home Page:
PGP Key:

Powered by blists - more mailing lists