From: Eric Biggers <ebiggers@kernel.org>
To: linux-fscrypt@vger.kernel.org
Cc: linux-ext4@vger.kernel.org
Subject: [PATCH] fscrypt: document gfp_flags for bounce page allocation
Date: Tue, 31 Dec 2019 12:10:26 -0600 [thread overview]
Message-ID: <20191231181026.47400-1-ebiggers@kernel.org> (raw)
From: Eric Biggers <ebiggers@google.com>
Document that fscrypt_encrypt_pagecache_blocks() allocates the bounce
page from a mempool, and document what this means for the @gfp_flags
argument.
Signed-off-by: Eric Biggers <ebiggers@google.com>
---
fs/crypto/crypto.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/fs/crypto/crypto.c b/fs/crypto/crypto.c
index fcc6ca792ba2..1ecaac7ee3cb 100644
--- a/fs/crypto/crypto.c
+++ b/fs/crypto/crypto.c
@@ -138,7 +138,7 @@ int fscrypt_crypt_block(const struct inode *inode, fscrypt_direction_t rw,
* multiple of the filesystem's block size.
* @offs: Byte offset within @page of the first block to encrypt. Must be
* a multiple of the filesystem's block size.
- * @gfp_flags: Memory allocation flags
+ * @gfp_flags: Memory allocation flags. See details below.
*
* A new bounce page is allocated, and the specified block(s) are encrypted into
* it. In the bounce page, the ciphertext block(s) will be located at the same
@@ -148,6 +148,11 @@ int fscrypt_crypt_block(const struct inode *inode, fscrypt_direction_t rw,
*
* This is for use by the filesystem's ->writepages() method.
*
+ * The bounce page allocation is mempool-backed, so it will always succeed when
+ * @gfp_flags includes __GFP_DIRECT_RECLAIM, e.g. when it's GFP_NOFS. However,
+ * only the first page of each bio can be allocated this way. To prevent
+ * deadlocks, for any additional pages a mask like GFP_NOWAIT must be used.
+ *
* Return: the new encrypted bounce page on success; an ERR_PTR() on failure
*/
struct page *fscrypt_encrypt_pagecache_blocks(struct page *page,
--
2.24.1
next reply other threads:[~2019-12-31 18:11 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-31 18:10 Eric Biggers [this message]
2020-01-13 19:36 ` [PATCH] fscrypt: document gfp_flags for bounce page allocation Theodore Y. Ts'o
2020-01-14 21:04 ` Eric Biggers
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20191231181026.47400-1-ebiggers@kernel.org \
--to=ebiggers@kernel.org \
--cc=linux-ext4@vger.kernel.org \
--cc=linux-fscrypt@vger.kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).