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
next prev parent 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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