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authorEric Biggers <ebiggers@google.com>2019-12-31 12:10:26 -0600
committerEric Biggers <ebiggers@google.com>2020-01-14 12:51:12 -0800
commit2d8f7f119b0b2ce5e7ff0e8024b0763bf42b99c9 (patch)
treef08d5430b86b860cc5c4020de52ba7ed21e25c0d /fs/crypto/crypto.c
parent796f12d742653028a1520cce3a76035c86e2ebf9 (diff)
fscrypt: document gfp_flags for bounce page allocation
Document that fscrypt_encrypt_pagecache_blocks() allocates the bounce page from a mempool, and document what this means for the @gfp_flags argument. Link: https://lore.kernel.org/r/20191231181026.47400-1-ebiggers@kernel.org Reviewed-by: Theodore Ts'o <tytso@mit.edu> Signed-off-by: Eric Biggers <ebiggers@google.com>
Diffstat (limited to 'fs/crypto/crypto.c')
-rw-r--r--fs/crypto/crypto.c7
1 files changed, 6 insertions, 1 deletions
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,