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From: Herbert Xu <herbert@gondor.apana.org.au>
To: Byungchul Park <byungchul.park@lge.com>
Cc: torvalds@linux-foundation.org, peterz@infradead.org,
	mingo@redhat.com, will@kernel.org, davem@davemloft.net,
	linux-crypto@vger.kernel.org, linux-kernel@vger.kernel.org,
	tglx@linutronix.de, rostedt@goodmis.org, joel@joelfernandes.org,
	alexander.levin@microsoft.com, daniel.vetter@ffwll.ch,
	chris@chris-wilson.co.uk, duyuyang@gmail.com,
	johannes.berg@intel.com, tj@kernel.org, tytso@mit.edu,
	willy@infradead.org, david@fromorbit.com, amir73il@gmail.com,
	bfields@fieldses.org, gregkh@linuxfoundation.org,
	kernel-team@lge.com
Subject: Re: [REPORT] Request for reviewing crypto code wrt wait_for_completion()
Date: Fri, 6 Aug 2021 19:40:58 +0800	[thread overview]
Message-ID: <20210806114058.GA13896@gondor.apana.org.au> (raw)
In-Reply-To: <20210806080344.GA5788@X58A-UD3R>

On Fri, Aug 06, 2021 at 05:03:44PM +0900, Byungchul Park wrote:
> Hello crypto folks,
> 
> I developed a tool for tracking waiters and reporting if any of the
> events that the waiters are waiting for would never happen, say, a
> deadlock. Yes, it would look like Lockdep but more inclusive.
> 
> While I ran the tool(Dept: Dependency Tracker) on v5.4.96, I got some
> reports from the tool. One of them is related to crypto subsystem.
> Because I'm not that familiar with the code, I'd like to ask you guys to
> review the related code.
> 
> If I understand correctly, it doesn't actually cause deadlock but looks
> like a problematic code. I know you are not used to the format of the
> report from Dept so.. let me summerize the result.
> 
> The simplified call trace looks like when the problem araised :
> 
> THREAD A
> --------
> A1 crypto_alg_mod_lookup()
> A2    crypto_probing_notify(CRYPTO_MSG_ALG_REQUEST)
> A3       cryptomgr_schedule_probe()
> A4          kthread_run(cyptomgr_probe) ---> Start THREAD B
> 
> A5    crypto_larval_wait()
> A6       wait_for_completion_killable_timeout(c) /* waiting for B10 */

This larval would be an instantiation larval, and it can only be
woken up by thread B, not C.

> THREAD B
> --------
> B1 cryptomgr_probe()
> B2    pkcslpad_create()
> B3       crypto_wait_for_test()
> B4          crypto_probing_notify(CRYPTO_MSG_ALG_REGISTER)
> B5             cryptomgr_schedule_test()
> B6                kthread_run(cyptomgr_test) ---> Start THREAD C
> 
> B7    tmpl->alloc()
> B8    crupto_register_instance()
> B9          wait_for_completion_killable(c) /* waiting for C3 */
> B10   complete_all(c)

I presume you're talking about about the wait_for_completion from
crypto_wait_for_test, in which case it can only be woken by thread
C.  After which thread B will return to cryptomgr_probe and wake up
thread A.

> THREAD C
> --------
> C1 cryptomgr_test()
> C2    crypto_alg_tested()
> C3       complete_all(c)
> 
> ---
> 
> For example, in this situation, I think C3 could wake up both A6 and B9
> before THREAD B reaches B10 which is not desired by A6. Say, is it okay
> to wake up A6 with B7 ~ B9 having yet to complete?

AFAICS thread C only wakes up test larvals, not instantiation larvals.
Please let me know if you have any further issues.

Thanks,
-- 
Email: Herbert Xu <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt

  reply	other threads:[~2021-08-06 11:41 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-03  2:16 [RFC] Cross-release versus a new tool Byungchul Park
2021-08-06  8:03 ` [REPORT] Request for reviewing crypto code wrt wait_for_completion() Byungchul Park
2021-08-06 11:40   ` Herbert Xu [this message]
2021-08-07  3:46     ` Byungchul Park
2021-08-08  4:45       ` Herbert Xu
2021-08-25  1:27 ` [RFC] Cross-release versus a new tool Byungchul Park

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