From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-lf1-f51.google.com (mail-lf1-f51.google.com [209.85.167.51]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E01F61CBEA6 for ; Fri, 6 Sep 2024 16:13:38 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.167.51 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1725639222; cv=none; b=U1UZBvOIUEh250u1TqaW8XaEYFawAt749e5U8tsQWElxlLssdJ0BlVZEIghC2ZeZma8pXbAcIn8sFrGqFptFL90D4Z+DJYwXSpoBfa0kaudq5aEd92ohg8kdDeccyzaSNzIa3EpkJ7EWP7Ksr4G9YKqiPngFCngPVo7jCIylN7s= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1725639222; c=relaxed/simple; bh=6qtHiDnxElIvPDVEWmhk2vdl1c+NLPGnxFLLq5CjDLs=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=XTtmhpL6nULTyAqlRWNLoiL2/At9bjWRYWOu0ACkhyWBdIlTIKLaxA7QcUIukcOnXzsbBupiUNzRHyW3iVDQZCtCJS12HolMzm0PJEjQRr97ZbYV/frXgJ0DA9qQgAvb/tQUDZNcE+nu5QhmeLJtUmUH3T5Ah5OBS9ukhv8yx/8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=suse.com; spf=pass smtp.mailfrom=suse.com; dkim=pass (2048-bit key) header.d=suse.com header.i=@suse.com header.b=SG5VoLbq; arc=none smtp.client-ip=209.85.167.51 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=suse.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=suse.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=suse.com header.i=@suse.com header.b="SG5VoLbq" Received: by mail-lf1-f51.google.com with SMTP id 2adb3069b0e04-5365392cfafso2049389e87.0 for ; Fri, 06 Sep 2024 09:13:38 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=google; t=1725639217; x=1726244017; darn=vger.kernel.org; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:from:to:cc:subject:date:message-id:reply-to; bh=adpXTAZO60azUV0Ob6AZV0dcnKEkcroMCFDVSYJYFSw=; b=SG5VoLbqRYDJQD07r1Hwfp4+dy13rpG1sO2FnbynJL1FAquihFOxFdXhViCxcAiHGO HPx9EB1Wjsy4UemusYDf+hsUl0cqNUo/nKQIwej8WDXRqpgrUITV750HvrlTT3yDkHLl Y0iWuSVBc4UJYD+DWYajpekl2GHLtLBAYqaPMQCZ5Jd7J1oMXUxxixGoHNb8IieBAAQm zwZ3NhR43bZsN0ueSsJJMJ517eyRnAgO+BN+Xw7Mo+znccAYwNhMg0jztylvWRanjiqT Bt7q/TkPLL+4Ep5wIpuZqFTHVtPKLOtBVTAyxtj4vXoKo1pEP2ffbFH0MFA822AmAWII YW5A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1725639217; x=1726244017; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=adpXTAZO60azUV0Ob6AZV0dcnKEkcroMCFDVSYJYFSw=; b=w+KU8jLClQNEEb53ipdnzZB7HIuA+ndH/eDFXFeV1Q4PzLiJoHqMQ9HYi5UJGnPSKr kWXqtQ7C7QRMP+qZfjxR7WK4epwdz75kia6WmYZA/FeT+Li75MdsNWMHwxjq52hT6shy tcu09zloieK9CJvbnsMAJ8M1Lu9U5oYAGaYRTes4uWhZOGF7yxcB7crNcpXHleIeGjOT 9IOX3EPKf+D1gbCYOpH3CP2yi4cWsaN0Zwhowukht2cDrLTGTD6Y1YZPh4lwwgXvbaKR MN+X9p3pXqpD8yCRcY7m+JDKYfexnVKIcdozzj8cDnwtc6H0xwJbIpN+ZOV9g+eF31Az 9IlA== X-Forwarded-Encrypted: i=1; AJvYcCVF1lZ3xtdRKcz18lhm4xnYKqwut+vezfaiRiFF2bWfLyeilX1x5YE+sn4PB/DCuF2zZ2K2nrADa2IvhDA=@vger.kernel.org X-Gm-Message-State: AOJu0Yx3LT3IMjhMMwapDqhxQcEvuoRx3rjcZ/zoVjjfIaselivYINFA vYZV00KTGOVxdQX8NYQ5rhmnwivtRkLZvgowFhrCn7taz6G9bgCgD2KBnNrP2Gc= X-Google-Smtp-Source: AGHT+IFajb+bsrzIRWA8ZFjiVGyZ+YpHk8riHh9kcXtlmaeSyrq2uJsF6Lk4kJ+PapFck/x8hOT71Q== X-Received: by 2002:a05:6512:1392:b0:533:809:a94d with SMTP id 2adb3069b0e04-536587ad9c5mr2317114e87.17.1725639216687; Fri, 06 Sep 2024 09:13:36 -0700 (PDT) Received: from pathway.suse.cz ([176.114.240.50]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-a8a61fbaf9esm294528466b.9.2024.09.06.09.13.35 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 06 Sep 2024 09:13:36 -0700 (PDT) Date: Fri, 6 Sep 2024 18:13:34 +0200 From: Petr Mladek To: Miroslav Benes Cc: Wardenjohn , jpoimboe@kernel.org, jikos@kernel.org, joe.lawrence@redhat.com, live-patching@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v4 2/2] livepatch: Add using attribute to klp_func for using function show Message-ID: References: <20240828022350.71456-1-zhangwarden@gmail.com> <20240828022350.71456-3-zhangwarden@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Thu 2024-09-05 12:23:20, Miroslav Benes wrote: > Hi, > > On Wed, 28 Aug 2024, Wardenjohn wrote: > > > One system may contains more than one livepatch module. We can see > > which patch is enabled. If some patches applied to one system > > modifing the same function, livepatch will use the function enabled > > on top of the function stack. However, we can not excatly know > > which function of which patch is now enabling. > > > > This patch introduce one sysfs attribute of "using" to klp_func. > > For example, if there are serval patches make changes to function > > "meminfo_proc_show", the attribute "enabled" of all the patch is 1. > > With this attribute, we can easily know the version enabling belongs > > to which patch. > > > > The "using" is set as three state. 0 is disabled, it means that this > > version of function is not used. 1 is running, it means that this > > version of function is now running. -1 is unknown, it means that > > this version of function is under transition, some task is still > > chaning their running version of this function. > > > > cat /sys/kernel/livepatch////using -> 0 > > means that the function1 of patch1 is disabled. > > > > cat /sys/kernel/livepatch////using -> 1 > > means that the function1 of patchN is enabled. > > > > cat /sys/kernel/livepatch////using -> -1 > > means that the function1 of patchN is under transition and unknown. > > > > Signed-off-by: Wardenjohn > > I am not a fan. Josh wrote most of my objections already so I will not > repeat them. I understand that the attribute might be useful but the > amount of code it adds to sensitive functions like > klp_complete_transition() is no fun. > > Would it be possible to just use klp_transition_patch and implement the > logic just in using_show()? I have not thought through it completely but > klp_transition_patch is also an indicator that there is a transition going > on. It is set to NULL only after all func->transition are false. So if you > check that, you can assign -1 in using_show() immediately and then just > look at the top of func_stack. The 1st patch adds the pointer to struct klp_ops into struct klp_func. We might check the state a similar way as klp_ftrace_handler(). I had something like this in mind when I suggested to move the pointer: static ssize_t using_show(struct kobject *kobj, struct kobj_attribute *attr, char *buf) { struct klp_func *func, *using_func; struct klp_ops *ops; int using; func = container_of(kobj, struct klp_func, kobj); rcu_read_lock(); if (func->transition) { using = -1; goto out; } # FIXME: This requires releasing struct klp_ops via call_rcu() ops = func->ops; if (!ops) { using = 0; goto out; } using_func = list_first_or_null_rcu(&ops->func_stack, struct klp_func, stack_node); if (func == using_func) using = 1; else using = 0; out: rcu_read_unlock(); return sysfs_emit(buf, "%d\n", func->using); } It is racy and tricky. We probably should add some memory barriers. And maybe even the ordering of reads should be different. We could not take klp_mutex because it might cause a deadlock when the sysfs file gets removed. kobject_put(&func->kobj) is called by __klp_free_funcs() under klp_mutex. It would be easier if we could take klp_mutex. But it would require decrementing the kobject refcout without of klp_mutex. It might be complicated. I am afraid that this approach is not worth the effort and is is not the way to go. Best Regards, Petr