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Subject[PATCH] fscrypt: avoid data race on fscrypt_mode::logged_impl_name
Date
From: Eric Biggers <ebiggers@google.com>

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.

Signed-off-by: Eric Biggers <ebiggers@google.com>
---
fs/crypto/keysetup.c | 6 ++----
1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/fs/crypto/keysetup.c b/fs/crypto/keysetup.c
index 8eb5a0e762ec6..df3e1c8653884 100644
--- a/fs/crypto/keysetup.c
+++ b/fs/crypto/keysetup.c
@@ -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, true)) {
/*
* 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);
--
2.23.0.581.g78d2f28ef7-goog
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