dm: disable CRYPTO_TFM_REQ_MAY_SLEEP to fix a GFP_KERNEL recursion deadlock
authorMikulas Patocka <mpatocka@redhat.com>
Wed, 5 Sep 2018 13:17:45 +0000 (09:17 -0400)
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Sat, 20 Apr 2019 07:15:08 +0000 (09:15 +0200)
commit8991f1af962d939c3f3456990f5a826c3aa628fd
treea20c998d4815c08f25c6c5eb0fe35c7b419b3ca1
parent02c2de9be3d031d5c0ee953ec342e5e0cabb3ed5
dm: disable CRYPTO_TFM_REQ_MAY_SLEEP to fix a GFP_KERNEL recursion deadlock

[ Upstream commit 432061b3da64e488be3403124a72a9250bbe96d4 ]

There's a XFS on dm-crypt deadlock, recursing back to itself due to the
crypto subsystems use of GFP_KERNEL, reported here:
https://bugzilla.kernel.org/show_bug.cgi?id=200835

* dm-crypt calls crypt_convert in xts mode
* init_crypt from xts.c calls kmalloc(GFP_KERNEL)
* kmalloc(GFP_KERNEL) recurses into the XFS filesystem, the filesystem
tries to submit some bios and wait for them, causing a deadlock

Fix this by updating both the DM crypt and integrity targets to no
longer use the CRYPTO_TFM_REQ_MAY_SLEEP flag, which will change the
crypto allocations from GFP_KERNEL to GFP_ATOMIC, therefore they can't
recurse into a filesystem.  A GFP_ATOMIC allocation can fail, but
init_crypt() in xts.c handles the allocation failure gracefully - it
will fall back to preallocated buffer if the allocation fails.

The crypto API maintainer says that the crypto API only needs to
allocate memory when dealing with unaligned buffers and therefore
turning CRYPTO_TFM_REQ_MAY_SLEEP off is safe (see this discussion:
https://www.redhat.com/archives/dm-devel/2018-August/msg00195.html )

Cc: stable@vger.kernel.org
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Sasha Levin (Microsoft) <sashal@kernel.org>
drivers/md/dm-crypt.c
drivers/md/dm-integrity.c