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(cst-prg-92-246.cust.vodafone.cz. [46.135.92.246]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-a7dc9e80df8sm545913166b.160.2024.08.06.06.36.15 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 06 Aug 2024 06:36:18 -0700 (PDT) From: Mateusz Guzik To: zohar@linux.ibm.com, roberto.sassu@huawei.com, paul@paul-moore.com, jmorris@namei.org, serge@hallyn.com Cc: linux-kernel@vger.kernel.org, linux-integrity@vger.kernel.org, linux-security-module@vger.kernel.org, Mateusz Guzik Subject: [PATCH] evm: stop avoidably reading i_writecount in evm_file_release Date: Tue, 6 Aug 2024 15:36:07 +0200 Message-ID: <20240806133607.869394-1-mjguzik@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-security-module@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 The EVM_NEW_FILE flag is unset if the file already existed at the time of open and this can be checked without looking at i_writecount. Not accessing it reduces traffic on the cacheline during parallel open of the same file and drop the evm_file_release routine from second place to bottom of the profile. Signed-off-by: Mateusz Guzik Reviewed-by: Roberto Sassu --- The context is that I'm writing a patch which removes one lockref get/put cycle on parallel open. An operational WIP reduces ping-pong in that area and made do_dentry_open skyrocket along with evm_file_release, due to i_writecount access. With the patch they go down again and apparmor takes the rightful first place. The patch accounts for about 5% speed up at 20 cores running open3 from will-it-scale on top of the above wip. (the apparmor + lockref thing really don't scale, that's next) I would provide better measurements, but the wip is not ready (as the description suggests) and I need evm out of the way for the actual patch. security/integrity/evm/evm_main.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c index 62fe66dd53ce..309630f319e2 100644 --- a/security/integrity/evm/evm_main.c +++ b/security/integrity/evm/evm_main.c @@ -1084,7 +1084,8 @@ static void evm_file_release(struct file *file) if (!S_ISREG(inode->i_mode) || !(mode & FMODE_WRITE)) return; - if (iint && atomic_read(&inode->i_writecount) == 1) + if (iint && iint->flags & EVM_NEW_FILE && + atomic_read(&inode->i_writecount) == 1) iint->flags &= ~EVM_NEW_FILE; }