Re: Stack traces in 2.6.9-rc2-mm4

From: Nick Piggin (nickpiggin_at_yahoo.com.au)
Date: 09/28/04

  • Next message: Alex Riesen: "Re: Switch back to Real mode and then boot strap" 
    Date:	Tue, 28 Sep 2004 20:48:32 +1000
To: Ingo Molnar <mingo@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.
    -
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