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From: Herbert Xu <>
To: Eric Biggers <>
	"Martin K . Petersen" <>,
	Mike Gerow <>
Subject: Re: [PATCH] crypto: algboss - don't wait during notifier callback
Date: Fri, 12 Jun 2020 16:48:29 +1000
Message-ID: <> (raw)
In-Reply-To: <>

On Thu, Jun 04, 2020 at 11:52:53AM -0700, Eric Biggers wrote:
> From: Eric Biggers <>
> When a crypto template needs to be instantiated, CRYPTO_MSG_ALG_REQUEST
> is sent to crypto_chain.  cryptomgr_schedule_probe() handles this by
> starting a thread to instantiate the template, then waiting for this
> thread to complete via crypto_larval::completion.
> This can deadlock because instantiating the template may require loading
> modules, and this (apparently depending on userspace) may need to wait
> for the crc-t10dif module (lib/crc-t10dif.c) to be loaded.  But
> crc-t10dif's module_init function uses crypto_register_notifier() and
> therefore takes crypto_chain.rwsem for write.  That can't proceed until
> the notifier callback has finished, as it holds this semaphore for read.
> Fix this by removing the wait on crypto_larval::completion from within
> cryptomgr_schedule_probe().  It's actually unnecessary because
> crypto_alg_mod_lookup() calls crypto_larval_wait() itself after sending
> This only actually became a problem in v4.20 due to commit b76377543b73
> ("crc-t10dif: Pick better transform if one becomes available"), but the
> unnecessary wait was much older.
> BugLink:
> Reported-by: Mike Gerow <>
> Fixes: 398710379f51 ("crypto: algapi - Move larval completion into algboss")
> Cc: <> # v3.6+
> Cc: Martin K. Petersen <>
> Signed-off-by: Eric Biggers <>
> ---
>  crypto/algboss.c | 2 --
>  1 file changed, 2 deletions(-)

Patch applied.  Thanks.
Email: Herbert Xu <>
Home Page:
PGP Key:

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Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-04 18:52 Eric Biggers
2020-06-04 20:08 ` Eric Biggers
2020-06-12  6:48 ` Herbert Xu [this message]

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