From: Eric Biggers <ebiggers@xxxxxxxxxx> 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@xxxxxxxxxx> --- 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
