* [PATCH] fscrypt: document gfp_flags for bounce page allocation
@ 2019-12-31 18:10 Eric Biggers
2020-01-13 19:36 ` Theodore Y. Ts'o
2020-01-14 21:04 ` Eric Biggers
0 siblings, 2 replies; 3+ messages in thread
From: Eric Biggers @ 2019-12-31 18:10 UTC (permalink / raw)
To: linux-fscrypt; +Cc: linux-ext4
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
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] fscrypt: document gfp_flags for bounce page allocation
2019-12-31 18:10 [PATCH] fscrypt: document gfp_flags for bounce page allocation Eric Biggers
@ 2020-01-13 19:36 ` Theodore Y. Ts'o
2020-01-14 21:04 ` Eric Biggers
1 sibling, 0 replies; 3+ messages in thread
From: Theodore Y. Ts'o @ 2020-01-13 19:36 UTC (permalink / raw)
To: Eric Biggers; +Cc: linux-fscrypt, linux-ext4
On Tue, Dec 31, 2019 at 12:10:26PM -0600, Eric Biggers wrote:
> 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>
Looks good, feel free to add:
Reviewed-by: Theodore Ts'o <tytso@mit.edu>
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] fscrypt: document gfp_flags for bounce page allocation
2019-12-31 18:10 [PATCH] fscrypt: document gfp_flags for bounce page allocation Eric Biggers
2020-01-13 19:36 ` Theodore Y. Ts'o
@ 2020-01-14 21:04 ` Eric Biggers
1 sibling, 0 replies; 3+ messages in thread
From: Eric Biggers @ 2020-01-14 21:04 UTC (permalink / raw)
To: linux-fscrypt; +Cc: linux-ext4
On Tue, Dec 31, 2019 at 12:10:26PM -0600, Eric Biggers wrote:
> 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(-)
Applied to fscrypt.git#master for 5.6.
- Eric
^ permalink raw reply [flat|nested] 3+ messages in thread
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