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    SubjectRe: Concurrent access to /dev/urandom
    On Wed, Dec 08, 2004 at 08:57:05PM -0500, Theodore Ts'o wrote:
    > On Wed, Dec 08, 2004 at 01:56:14PM -0800, Matt Mackall wrote:
    > >
    > > Ted, I think this is a bit more straightforward than your patch, and
    > > safer as it protects get_random_bytes() and internal extract_entropy()
    > > users. And I'd be leery of your get_cpu() trick due to preempt
    > > issues.
    > >
    >
    > I'm concerned that turning off interrupts during even a single SHA-1
    > transform will put us above the radar with respect to the preempt
    > latency statistics again. We could use a separate spinlock that only
    > pretects the mix_ptr and mixing access to the pool, so we're at least
    > not disabling interrupts, but we still are holding a spinlock across a
    > cryptographic operation.

    It's been suggested to me that a sequence lock might be the right
    approach to this, which I'll try to take a look at this evening. Also,
    I'm going to time the lock hold time in my previous more conventional
    patch and see what kind of neighborhood we're in.

    --
    Mathematics is the supreme nostalgia of our time.
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