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From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: John Mathew <john.mathew@unikie.com>
Cc: linux-rt-users@vger.kernel.org, lukas.bulwahn@gmail.com
Subject: Re: complete_all() with x waiters in swake_up_all_locked
Date: Wed, 18 Dec 2019 17:53:34 +0100
Message-ID: <20191218165334.k4suur4gzlu62ibs@linutronix.de> (raw)
In-Reply-To: <CAJz2qXnPquUZSeO9SWSmvLKcdhnT96KnD66F-oatdnotYkxS+A@mail.gmail.com>

On 2019-12-13 11:08:35 [+0200], John Mathew wrote:
> 
> I was able to reproduce the warning on v5.2.21-rt14 which is the
> latest tag on the rt-devel branch.
> Here is my analysis.
> What I see is that in crypto/algboss.c there is a probe being
> scheduled when a notification arrives.
> The probe will run a thread: cryptomgr_probe and wait for its completion.
> The issue arises because a similar module is also issues a wait for
> completion on the exactly same completion object (larval->completion).
> The similar module is:  crypto_larval_wait in linux-rt-devel/crypto/api.c
> It is casting a crypto_larval struct pointer from a crypto_alg struct
> pointer which doesn't seem to have/init a completion object.

It should. container_of() statement would be better.

> So it is actually the cryptomgr_probe thread that actually completes
> both its own and the crypto_larval_wait waits and so the number of
> completions exceeds the limit of 2.
> 
> This looks like an error to me.

Why? So multiple threads request a specific algorithm. This is
synchronized into one request which (once complete) invokes
complete_all() to wake all requesting threads. So this does not sound
bad. 
I compiled and tested the syzkaller testcase but still no luck. Is there
something special to you .config?

> So I created patch in the following email.
> I don't think the issue is with the limit, rather a wrong usage of the
> completion object.

But why is there no other error? Like wrong list usage, uninitialized
spin_lock, etc.?

> > > -John

 Sebastian

  reply index

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-12-11  7:17 John Mathew
2019-12-12 17:12 ` Sebastian Andrzej Siewior
2019-12-13  9:08   ` John Mathew
2019-12-18 16:53     ` Sebastian Andrzej Siewior [this message]
2019-12-31 10:00       ` [PATCH] crypto: only wait for completion once John Mathew
2020-01-14 12:47         ` Sebastian Andrzej Siewior
2020-02-11 11:48           ` John Mathew
2020-02-11 12:04             ` Sebastian Andrzej Siewior
2020-02-11 15:52               ` John Mathew
2020-02-11 15:59                 ` Sebastian Andrzej Siewior
2020-02-12 12:55                   ` John Mathew
2020-02-12 17:02                     ` Sebastian Andrzej Siewior
2020-02-13  6:58                       ` John Mathew
2020-02-13  8:31                         ` Sebastian Andrzej Siewior
2020-02-18  7:18                           ` [PATCH] swait: Increase number of waiters for warning John Mathew
2020-03-20 16:54                             ` [PATCH RT] swait: Remove the warning with more than two waiters Sebastian Andrzej Siewior

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