On Sun, Feb 09, 2020 at 12:26:01PM +0100, gregkh@xxxxxxxxxxxxxxxxxxx wrote:
The patch below does not apply to the 4.19-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@xxxxxxxxxxxxxxx>.
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From 547c556f4db7c09447ecf5f833ab6aaae0c5ab58 Mon Sep 17 00:00:00 2001
From: Eric Biggers <ebiggers@xxxxxxxxxx>
Date: Tue, 31 Dec 2019 12:11:49 -0600
Subject: [PATCH] ext4: fix deadlock allocating crypto bounce page from mempool
ext4_writepages() on an encrypted file has to encrypt the data, but it
can't modify the pagecache pages in-place, so it encrypts the data into
bounce pages and writes those instead. All bounce pages are allocated
from a mempool using GFP_NOFS.
This is not correct use of a mempool, and it can deadlock. This is
because GFP_NOFS includes __GFP_DIRECT_RECLAIM, which enables the "never
fail" mode for mempool_alloc() where a failed allocation will fall back
to waiting for one of the preallocated elements in the pool.
But since this mode is used for all a bio's pages and not just the
first, it can deadlock waiting for pages already in the bio to be freed.
This deadlock can be reproduced by patching mempool_alloc() to pretend
that pool->alloc() always fails (so that it always falls back to the
preallocations), and then creating an encrypted file of size > 128 KiB.
Fix it by only using GFP_NOFS for the first page in the bio. For
subsequent pages just use GFP_NOWAIT, and if any of those fail, just
submit the bio and start a new one.
This will need to be fixed in f2fs too, but that's less straightforward.
Fixes: c9af28fdd449 ("ext4 crypto: don't let data integrity writebacks fail with ENOMEM")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20191231181149.47619-1-ebiggers@xxxxxxxxxx
Signed-off-by: Theodore Ts'o <tytso@xxxxxxx>
I've worked around not having these patches:
592ddec7578a ("ext4: use IS_ENCRYPTED() to check encryption status")
53bc1d854c64 ("fscrypt: support encrypting multiple filesystem blocks per page")
d2d0727b1654 ("fscrypt: simplify bounce page handling")
And queued the backport to 4.19-4.4.
--
Thanks,
Sasha
