From: Eric Biggers <ebiggers@kernel.org>
To: linux-fscrypt@vger.kernel.org
Cc: "Theodore Y . Ts'o" <tytso@mit.edu>,
Jaegeuk Kim <jaegeuk@kernel.org>,
linux-kernel@vger.kernel.org
Subject: [PATCH v2] fscrypt: avoid data race on fscrypt_mode::logged_impl_name
Date: Mon, 21 Oct 2019 13:49:03 -0700 [thread overview]
Message-ID: <20191021204903.56528-1-ebiggers@kernel.org> (raw)
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.
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>
---
fs/crypto/fscrypt_private.h | 2 +-
fs/crypto/keysetup.c | 6 ++----
2 files changed, 3 insertions(+), 5 deletions(-)
diff --git a/fs/crypto/fscrypt_private.h b/fs/crypto/fscrypt_private.h
index dacf8fcbac3be..d9a3e8614049f 100644
--- a/fs/crypto/fscrypt_private.h
+++ b/fs/crypto/fscrypt_private.h
@@ -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
diff --git a/fs/crypto/keysetup.c b/fs/crypto/keysetup.c
index b03b33643e4b2..28bc2da9be3c7 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, 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);
--
2.23.0.866.gb869b98d4c-goog
next reply other threads:[~2019-10-21 20:49 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-21 20:49 Eric Biggers [this message]
2019-11-06 21:02 ` [PATCH v2] fscrypt: avoid data race on fscrypt_mode::logged_impl_name Eric Biggers
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