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Subject: Re: Linux 5.3-rc8
To:     Willy Tarreau <w@1wt.eu>, Lennart Poettering <mzxreary@0pointer.de>
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From:   "Alexander E. Patrakov" <patrakov@gmail.com>
Message-ID: <69d8cabe-9285-a01e-ae78-57838e886c9a@gmail.com>
Date:   Tue, 17 Sep 2019 22:41:33 +0500
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17.09.2019 22:32, Willy Tarreau пишет:
> On Tue, Sep 17, 2019 at 07:30:36PM +0200, Lennart Poettering wrote:
>> On Di, 17.09.19 21:58, Alexander E. Patrakov (patrakov@gmail.com) wrote:
>>
>>> I am worried that the getrandom delays will be serialized, because processes
>>> sometimes run one after another. If there are enough chained/dependent
>>> processes that ask for randomness before it is ready, the end result is
>>> still a too-big delay, essentially a failed boot.
>>>
>>> In other words: your approach of adding delays only makes sense for heavily
>>> parallelized boot, which may not be the case, especially for embedded
>>> systems that don't like systemd.
>>
>> As mentioned elsewhere: once the pool is initialized it's
>> initialized. This means any pending getrandom() on the whole system
>> will unblock at the same time, and from the on all getrandom()s will
>> be non-blocking.
> 
> He means that all process will experience this delay until there's enough
> entropy.
> 
> Willy

Indeed, my wording was not clear enough. Linus' patch has a 5-second 
timeout for small entropy requests, after which they get converted to 
the equivalent of urandom. However, in the following shell script:

#!/bin/sh
p1
p2

if both p1 and p2 ask for a small amount of entropy before crng is fully 
initialized, and do nothing that produces more entropy, the total delay 
will be 10 seconds.

-- 
Alexander E. Patrakov