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Mon, 6 May 2019 05:11:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=codeaurora.org; s=default; t=1557119506; bh=DqprrUG2On7X5AKgP2JeFG6hrsMFcEW8ibKQnnEvhHY=; h=Subject:To:Cc:References:From:Date:In-Reply-To:From; b=ToyvBRQrYExvL/0GBr9aGynzIpkZ2XA1tkUZlTTr7w37yt3FZceAsUcTUl6nVB0NH kjzFIvywK8VONhlSapNbTu82WfP1jGdyH3UGnG9goH37biE9fKYr/0vFr6oZWwCqyn eKPNQUVf95LgE49QafhJAcBvINfy78ea7nMEZb+o= DMARC-Filter: OpenDMARC Filter v1.3.2 smtp.codeaurora.org 94D2660DA8 Authentication-Results: pdx-caf-mail.web.codeaurora.org; dmarc=none (p=none dis=none) header.from=codeaurora.org Authentication-Results: pdx-caf-mail.web.codeaurora.org; spf=none smtp.mailfrom=prsood@codeaurora.org Subject: Re: [PATCH v3] drivers: core: Remove glue dirs early only when refcount is 1 To: gregkh@linuxfoundation.org, rafael@kernel.org Cc: sramana@codeaurora.org, linux-kernel@vger.kernel.org References: <20190501065313.GA30616@kroah.com> <1556711999-16898-1-git-send-email-prsood@codeaurora.org> From: Prateek Sood Message-ID: <0aac6bf3-6691-7c5a-31f1-fb7231c6b585@codeaurora.org> Date: Mon, 6 May 2019 10:41:34 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: <1556711999-16898-1-git-send-email-prsood@codeaurora.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 5/1/19 5:29 PM, Prateek Sood wrote: > While loading firmware blobs parallely in different threads, it is possible > to free sysfs node of glue_dirs in device_del() from a thread while another > thread is trying to add subdir from device_add() in glue_dirs sysfs node. > > CPU1 CPU2 > fw_load_sysfs_fallback() > device_add() > get_device_parent() > class_dir_create_and_add() > kobject_add_internal() > create_dir() // glue_dir > > fw_load_sysfs_fallback() > device_add() > get_device_parent() > kobject_get() //glue_dir > > device_del() > cleanup_glue_dir() > kobject_del() > > kobject_add() > kobject_add_internal() > create_dir() // in glue_dir > kernfs_create_dir_ns() > > sysfs_remove_dir() //glue_dir->sd=NULL > sysfs_put() // free glue_dir->sd > > kernfs_new_node() > kernfs_get(glue_dir) > > Fix this race by making sure that kernfs_node for glue_dir is released only > when refcount for glue_dir kobj is 1. > > Signed-off-by: Prateek Sood > > --- > > Changes from v2->v3: > - Added patch version change related comments. > > Changes from v1->v2: > - Updated callstack from _request_firmware_load() to fw_load_sysfs_fallback(). > > > drivers/base/core.c | 5 ++++- > 1 file changed, 4 insertions(+), 1 deletion(-) > > diff --git a/drivers/base/core.c b/drivers/base/core.c > index 4aeaa0c..3955d07 100644 > --- a/drivers/base/core.c > +++ b/drivers/base/core.c > @@ -1820,12 +1820,15 @@ static inline struct kobject *get_glue_dir(struct device *dev) > */ > static void cleanup_glue_dir(struct device *dev, struct kobject *glue_dir) > { > + unsigned int refcount; > + > /* see if we live in a "glue" directory */ > if (!live_in_glue_dir(glue_dir, dev)) > return; > > mutex_lock(&gdp_mutex); > - if (!kobject_has_children(glue_dir)) > + refcount = kref_read(&glue_dir->kref); > + if (!kobject_has_children(glue_dir) && !--refcount) > kobject_del(glue_dir); > kobject_put(glue_dir); > mutex_unlock(&gdp_mutex); > Folks, Please share feedback on the race condition and the patch to fix it. -- Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center, Inc., is a member of Code Aurora Forum, a Linux Foundation Collaborative Project