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Date: Tue, 29 Nov 2016 04:04:05 -0800
From: Christoph Hellwig <hch@infradead.org>
Subject: Re: XFS on RBD deadlock
Message-ID: <20161129120405.GA11089@infradead.org>
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To: Lucas Stach <l.stach@pengutronix.de>
Cc: ceph-devel@vger.kernel.org, linux-xfs@vger.kernel.org, Michael Olbrich <m.olbrich@pengutronix.de>, =?iso-8859-1?Q?Bj=F6rn_L=E4ssig?= <b.laessig@pengutronix.de>

On Tue, Nov 29, 2016 at 12:17:08PM +0100, Lucas Stach wrote:
> 2. RBD worker is trying to handle the XFS block request, but the
> involved crypto code recurses into the XFS superblock shrinker, as it's
> trying to allocate memory with GFP_KERNEL in __crypto_alloc_tfm.

And that's where the issues start - crypto_alloc_skcipher and friends
are not intended to be called from the writeback path.