From: Eric Biggers ebiggers@google.com
commit 547c556f4db7c09447ecf5f833ab6aaae0c5ab58 upstream.
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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- fs/ext4/page-io.c | 19 ++++++++++++++----- 1 file changed, 14 insertions(+), 5 deletions(-)
--- a/fs/ext4/page-io.c +++ b/fs/ext4/page-io.c @@ -478,17 +478,26 @@ int ext4_bio_write_page(struct ext4_io_s gfp_t gfp_flags = GFP_NOFS; unsigned int enc_bytes = round_up(len, i_blocksize(inode));
+ /* + * Since bounce page allocation uses a mempool, we can only use + * a waiting mask (i.e. request guaranteed allocation) on the + * first page of the bio. Otherwise it can deadlock. + */ + if (io->io_bio) + gfp_flags = GFP_NOWAIT | __GFP_NOWARN; retry_encrypt: bounce_page = fscrypt_encrypt_pagecache_blocks(page, enc_bytes, 0, gfp_flags); if (IS_ERR(bounce_page)) { ret = PTR_ERR(bounce_page); - if (ret == -ENOMEM && wbc->sync_mode == WB_SYNC_ALL) { - if (io->io_bio) { + if (ret == -ENOMEM && + (io->io_bio || wbc->sync_mode == WB_SYNC_ALL)) { + gfp_flags = GFP_NOFS; + if (io->io_bio) ext4_io_submit(io); - congestion_wait(BLK_RW_ASYNC, HZ/50); - } - gfp_flags |= __GFP_NOFAIL; + else + gfp_flags |= __GFP_NOFAIL; + congestion_wait(BLK_RW_ASYNC, HZ/50); goto retry_encrypt; } bounce_page = NULL;