linux-kernel - Re: Process Hang in __read_seqcount

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:	Mon, 22 Oct 2012 10:25:42 -0700
From:	Peter LaDow <petela@...ougs.wsu.edu>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: Process Hang in __read_seqcount_begin

On Mon, Oct 22, 2012 at 10:01 AM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> This looks like a corruption of s->sequence, and is value is odd, even
> if no writer is alive.
>
> Does local_bh_disable() disables preemption on RT ?

Hmmm....

With PREEMPT_RT_FULL defined (as we have):

void local_bh_disable(void)
{
        migrate_disable();
        current->softirq_nestcnt++;
}

And the RT patches add the following:

#ifdef CONFIG_PREEMPT_RT_FULL
# define preempt_disable_rt()          preempt_disable()
# define preempt_enable_rt()           preempt_enable()
# define preempt_disable_nort()                do { } while (0)
# define preempt_enable_nort()         do { } while (0)
# ifdef CONFIG_SMP
   extern void migrate_disable(void);
   extern void migrate_enable(void);
# else /* CONFIG_SMP */
#  define migrate_disable()            do { } while (0)
#  define migrate_enable()             do { } while (0)
# endif /* CONFIG_SMP */
#else
# define preempt_disable_rt()          do { } while (0)
# define preempt_enable_rt()           do { } while (0)
# define preempt_disable_nort()                preempt_disable()
# define preempt_enable_nort()         preempt_enable()
# define migrate_disable()             preempt_disable()
# define migrate_enable()              preempt_enable()
#endif

And since we are not SMP, local_bh_disable() essentially does nothing.
 These definitions are consistent across all the RT patches, up to
3.6.2-rt4 (as far as I can tell).

Now, is preemption required to be disabled in non-SMP systems?
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/