evm: stop avoidably reading i_writecount in evm_file_release

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.

Fixes: 75a323e ("evm: Make it independent from 'integrity' LSM")
Signed-off-by: Mateusz Guzik <[email protected]>
Reviewed-by: Roberto Sassu <[email protected]>
Cc: [email protected] # 6.9+
Signed-off-by: Mimi Zohar <[email protected]>

Author: mjguzik

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;
 }