linux-ext4 - Re: Linux 5.3-rc8

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Date:   Tue, 17 Sep 2019 22:41:33 +0500
From:   "Alexander E. Patrakov" <patrakov@...il.com>
To:     Willy Tarreau <w@....eu>, Lennart Poettering <mzxreary@...inter.de>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Matthew Garrett <mjg59@...f.ucam.org>,
        "Ahmed S. Darwish" <darwish.07@...il.com>,
        "Theodore Y. Ts'o" <tytso@....edu>,
        Vito Caputo <vcaputo@...garu.com>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        Jan Kara <jack@...e.cz>, Ray Strode <rstrode@...hat.com>,
        William Jon McCann <mccann@....edu>,
        zhangjs <zachary@...shancloud.com>, linux-ext4@...r.kernel.org,
        lkml <linux-kernel@...r.kernel.org>
Subject: Re: Linux 5.3-rc8

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@...il.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