Re: FAILED: patch "[PATCH] ext4: fix deadlock allocating crypto bounce page from mempool" failed to apply to 4.19-stable tree

[Sasha Levin <sashal@kernel.org>]

On Sun, Feb 09, 2020 at 12:26:01PM +0100, gregkh@linuxfoundation.org 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@vger.kernel.org>.
>
>thanks,
>
>greg k-h
>
>------------------ original commit in Linus's tree ------------------
>
>From 547c556f4db7c09447ecf5f833ab6aaae0c5ab58 Mon Sep 17 00:00:00 2001
>From: Eric Biggers <ebiggers@google.com>
>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@vger.kernel.org
>Signed-off-by: Eric Biggers <ebiggers@google.com>
>Link: https://lore.kernel.org/r/20191231181149.47619-1-ebiggers@kernel.org
>Signed-off-by: Theodore Ts'o <tytso@mit.edu>

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