From: Nick Piggin <nickpiggin@yahoo.com.au>
To: Ingo Molnar <mingo@elte.hu>
Cc: "J.A. Magallon" <jamagallon@able.es>,
linux-kernel@vger.kernel.org, Andrew Morton <akpm@osdl.org>,
tytso@mit.edu
Subject: Re: Stack traces in 2.6.9-rc2-mm4
Date: Tue, 28 Sep 2004 20:48:32 +1000 [thread overview]
Message-ID: <41594180.3010906@yahoo.com.au> (raw)
In-Reply-To: <20040928102454.GA20271@elte.hu>
Ingo Molnar wrote:
> * Nick Piggin <nickpiggin@yahoo.com.au> wrote:
>
>
>>>+ preempt_disable();
>>> /* if over the trickle threshold, use only 1 in 4096 samples */
>>> if ( random_state->entropy_count > trickle_thresh &&
>>> (__get_cpu_var(trickle_count)++ & 0xfff))
>>>- return;
>>>+ goto out;
>>>
>>
>>It looks like upstream code *is* buggy because that is a non-atomic
>>RMW operation on the per-cpu var, no? Hence you must disable preempt.
>
>
> no, the upstream code (i.e. BK-curr) is not buggy, because there this
> code runs under the BKL, implicitly as part of vt_ioctl() - and the BKL
> disables preemption in the upstream kernel.
>
> Yes, the code is fragile, but it's not buggy. With the remove-bkl patch
> this fragility turned into an outright bug. (Fortunately the patch
> detects all such incidents.)
>
Ahh yeah you're right, sorry.
next prev parent reply other threads:[~2004-09-28 10:48 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-09-27 8:01 Stack traces in 2.6.9-rc2-mm4 Reuben Farrelly
2004-09-27 8:23 ` Nick Piggin
2004-09-27 8:57 ` Ingo Molnar
2004-09-27 9:14 ` Reuben Farrelly
2004-09-27 23:12 ` J.A. Magallon
2004-09-28 7:21 ` Ingo Molnar
2004-09-28 7:49 ` Nick Piggin
2004-09-28 10:24 ` Ingo Molnar
2004-09-28 10:48 ` Nick Piggin [this message]
2004-09-30 21:58 ` J.A. Magallon
2004-09-30 22:56 ` Ingo Molnar
2004-09-30 23:16 ` J.A. Magallon
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