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author | Eric Biggers <ebiggers@google.com> | 2019-12-31 12:11:49 -0600 |
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committer | Theodore Ts'o <tytso@mit.edu> | 2020-01-17 16:24:54 -0500 |
commit | 547c556f4db7c09447ecf5f833ab6aaae0c5ab58 (patch) | |
tree | 085e8baa73457069e7141a2da4151aacd608f344 | |
parent | 8f27fd0ab569f5d09410010b15a3f45399e89fcf (diff) | |
download | linux-547c556f4db7c09447ecf5f833ab6aaae0c5ab58.tar.bz2 |
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>
-rw-r--r-- | fs/ext4/page-io.c | 19 |
1 files changed, 14 insertions, 5 deletions
diff --git a/fs/ext4/page-io.c b/fs/ext4/page-io.c index 24aeedb8fc75..68b39e75446a 100644 --- a/fs/ext4/page-io.c +++ b/fs/ext4/page-io.c @@ -512,17 +512,26 @@ int ext4_bio_write_page(struct ext4_io_submit *io, 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; } |