Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932380AbdCWHhe (ORCPT ); Thu, 23 Mar 2017 03:37:34 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:42808 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753669AbdCWHhW (ORCPT ); Thu, 23 Mar 2017 03:37:22 -0400 Date: Thu, 23 Mar 2017 08:18:50 +0100 From: "gregkh@linuxfoundation.org" To: Ajay Kaher Cc: Alan Stern , "linux-usb@vger.kernel.org" , "linux-kernel@vger.kernel.org" , AMAN DEEP , HEMANSHU SRIVASTAVA Subject: Re: [PATCH v4] USB: Proper handling of Race Condition when two USB class drivers try to call init_usb_class simultaneously Message-ID: <20170323071850.GA13002@kroah.com> References: <20170309121041.GB13054@kroah.com> <20170309113425epcms5p783be90da82c183653eafed97413469c4@epcms5p7> <20170317105637epcms5p2d296f449d5c5712718d6efab69948985@epcms5p2> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170317105637epcms5p2d296f449d5c5712718d6efab69948985@epcms5p2> User-Agent: Mutt/1.8.0 (2017-02-23) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2765 Lines: 79 On Fri, Mar 17, 2017 at 10:56:37AM +0000, Ajay Kaher wrote: > There is race condition when two USB class drivers try to call > init_usb_class at the same time and leads to crash. > code path: probe->usb_register_dev->init_usb_class > > To solve this, mutex locking has been added in init_usb_class() and > destroy_usb_class(). > > As pointed by Alan, removed "if (usb_class)" test from destroy_usb_class() > because usb_class can never be NULL there. > > Signed-off-by: Ajay Kaher > Acked-by: Alan Stern > --- > drivers/usb/core/file.c | 9 +++++++-- > 1 file changed, 7 insertions(+), 2 deletions(-) > > diff --git a/drivers/usb/core/file.c b/drivers/usb/core/file.c > index 822ced9..422ce7b 100644 > --- a/drivers/usb/core/file.c > +++ b/drivers/usb/core/file.c > @@ -27,6 +27,7 @@ > #define MAX_USB_MINORS 256 > static const struct file_operations *usb_minors[MAX_USB_MINORS]; > static DECLARE_RWSEM(minor_rwsem); > +static DEFINE_MUTEX(init_usb_class_mutex); > > static int usb_open(struct inode *inode, struct file *file) > { > @@ -109,8 +110,9 @@ static void release_usb_class(struct kref *kref) > > static void destroy_usb_class(void) > { > - if (usb_class) > - kref_put(&usb_class->kref, release_usb_class); > + mutex_lock(&init_usb_class_mutex); > + kref_put(&usb_class->kref, release_usb_class); > + mutex_unlock(&init_usb_class_mutex); > } > > int usb_major_init(void) > @@ -171,7 +173,10 @@ int usb_register_dev(struct usb_interface *intf, > if (intf->minor >= 0) > return -EADDRINUSE; > > + mutex_lock(&init_usb_class_mutex); > retval = init_usb_class(); > + mutex_unlock(&init_usb_class_mutex); > + > if (retval) > return retval; > I get the following errors when trying to apply this patch: Applying: USB: Proper handling of Race Condition when two USB class drivers try to call init_usb_class simultaneously .git/rebase-apply/patch:13: trailing whitespace. static DEFINE_MUTEX(init_usb_class_mutex); .git/rebase-apply/patch:23: trailing whitespace. mutex_lock(&init_usb_class_mutex); .git/rebase-apply/patch:24: trailing whitespace. kref_put(&usb_class->kref, release_usb_class); .git/rebase-apply/patch:25: trailing whitespace. mutex_unlock(&init_usb_class_mutex); .git/rebase-apply/patch:33: trailing whitespace. mutex_lock(&init_usb_class_mutex); error: patch failed: drivers/usb/core/file.c:27 error: drivers/usb/core/file.c: patch does not apply Patch failed at 0001 USB: Proper handling of Race Condition when two USB class drivers try to call init_usb_class simultaneously Are you sure you made this in the correct format? Seems that the patch has dos line-ends :( Please fix up and resend. thanks, greg k-h