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fscrypt: avoid data race on fscrypt_mode::logged_impl_name

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The access to logged_impl_name is technically a data race, which tools
like KCSAN could complain about in the future.  See:
https://github.com/google/ktsan/wiki/READ_ONCE-and-WRITE_ONCE

Fix by using xchg(), which also ensures that only one thread does the
logging.

This also required switching from bool to int, to avoid a build error on
the RISC-V architecture which doesn't implement xchg on bytes.

Signed-off-by: Eric Biggers <ebiggers@google.com>
This commit is contained in:
Eric Biggers 2019-10-21 13:49:03 -07:00
parent 065ab4c470
commit ff73c2c016
2 changed files with 3 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
fs/crypto/fscrypt_private.h
View File

@ -435,7 +435,7 @@ struct fscrypt_mode {
const char *cipher_str;
int keysize;
int ivsize;
bool logged_impl_name;
int logged_impl_name;
};
static inline bool

6
fs/crypto/keysetup.c
View File

@ -81,15 +81,13 @@ struct crypto_skcipher *fscrypt_allocate_skcipher(struct fscrypt_mode *mode,
mode->cipher_str, PTR_ERR(tfm));
return tfm;
}
if (unlikely(!mode->logged_impl_name)) {
if (!xchg(&mode->logged_impl_name, 1)) {
/*
* fscrypt performance can vary greatly depending on which
* crypto algorithm implementation is used. Help people debug
* performance problems by logging the ->cra_driver_name the
* first time a mode is used. Note that multiple threads can
* race here, but it doesn't really matter.
* first time a mode is used.
*/
mode->logged_impl_name = true;
pr_info("fscrypt: %s using implementation \"%s\"\n",
mode->friendly_name,
crypto_skcipher_alg(tfm)->base.cra_driver_name);