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From: Pavel Skripkin <paskripkin@gmail.com>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Larry Finger <Larry.Finger@lwfinger.net>,
	Phillip Potter <phil@philpotter.co.uk>
Cc: linux-staging@lists.linux.dev, linux-kernel@vger.kernel.org,
	David Laight <david.Laight@aculab.com>,
	Dan Carpenter <dan.carpenter@oracle.com>,
	"Fabio M. De Francesco" <fmdefrancesco@gmail.com>
Subject: Re: [PATCH v7 19/19] staging: r8188eu: remove shared buffer for usb requests
Date: Fri, 17 Sep 2021 18:03:52 +0300	[thread overview]
Message-ID: <ef2a89f5-f68c-e7e2-9338-78e70dc41701@gmail.com> (raw)
In-Reply-To: <YUSsa+3NjQVGD9gb@kroah.com>

On 9/17/21 17:55, Greg Kroah-Hartman wrote:
> On Fri, Sep 17, 2021 at 09:18:37AM +0200, Fabio M. De Francesco wrote:
>> From: Pavel Skripkin <paskripkin@gmail.com>
>> 
>> This driver used shared buffer for usb requests. It led to using
>> mutexes, i.e no usb requests can be done in parallel.
>> 
>> USB requests can be fired in parallel since USB Core allows it. In
>> order to allow them, remove usb_vendor_req_buf from dvobj_priv (since
>> USB I/O is the only user of it) and remove also usb_vendor_req_mutex
>> (since there is nothing to protect).
> 
> Ah, you are removing this buffer, nice!
> 
> But, just because the USB core allows multiple messages to be sent to a
> device at the same time, does NOT mean that the device itself can handle
> that sort of a thing.
> 
> Keeping that lock might be a good idea, until you can prove otherwise.
> You never know, maybe there's never any contention at all for it because
> these accesses are all done in a serial fashion and the lock
> grab/release is instant.  But if that is not the case, you might really
> get a device confused here by throwing multiple control messages at it
> in ways that it is not set up to handle at all.
> 
> So please do not drop the lock.
> 
> More comments below.
> 

We have tested this change. I've tested it in qemu with TP-Link 
TL-WN722N v2 / v3 [Realtek RTL8188EUS], and Fabio has tested it on his 
host for like a whole evening.

I agree, that our testing does not cover all possible cases and I can't 
say it was "good stress testing", so, I think, we need some comments 
from maintainers.

@Larry, @Phillip, does this change looks reasonable for this chip?



With regards,
Pavel Skripkin

> 
>> 
>> Co-developed-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
>> Signed-off-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
>> Signed-off-by: Pavel Skripkin <paskripkin@gmail.com>
>> ---
>>  drivers/staging/r8188eu/hal/usb_ops_linux.c | 29 ++++++++-------
>>  drivers/staging/r8188eu/include/drv_types.h |  5 ---
>>  drivers/staging/r8188eu/os_dep/usb_intf.c   | 40 ++-------------------
>>  3 files changed, 16 insertions(+), 58 deletions(-)
>> 
>> diff --git a/drivers/staging/r8188eu/hal/usb_ops_linux.c b/drivers/staging/r8188eu/hal/usb_ops_linux.c
>> index 656f3a774e48..0ed4e6c8b1f5 100644
>> --- a/drivers/staging/r8188eu/hal/usb_ops_linux.c
>> +++ b/drivers/staging/r8188eu/hal/usb_ops_linux.c
>> @@ -19,9 +19,9 @@ static int usb_read(struct intf_hdl *intfhdl, u16 addr, void *data, u8 size)
>>  	if (adapt->bSurpriseRemoved || adapt->pwrctrlpriv.pnp_bstop_trx)
>>  		return -EPERM;
>>  
>> -	mutex_lock(&dvobjpriv->usb_vendor_req_mutex);
>> -
>> -	io_buf = dvobjpriv->usb_vendor_req_buf;
>> +	io_buf = kmalloc(size, GFP_KERNEL);
>> +	if (!io_buf)
>> +		return -ENOMEM;
> 
> Please read the docs for usb_control_msg_recv().  It can allow data off
> of the stack, so no need to allocate/free the buffer like this all the
> time.
> 
> Note, the usb_control_msg() call does require the data to be allocated
> dynamically, like the code does today.  Which is why you probably got
> confused here.
> 
> Same for usb_control_msg_send(), it can take data off of the stack.
> 
> 
>>  
>>  	status = usb_control_msg_recv(udev, 0, REALTEK_USB_VENQT_CMD_REQ,
>>  				      REALTEK_USB_VENQT_READ, addr,
>> @@ -39,7 +39,7 @@ static int usb_read(struct intf_hdl *intfhdl, u16 addr, void *data, u8 size)
>>  		 * exist or is not enabled.
>>  		 */
>>  		adapt->bSurpriseRemoved = true;
>> -		goto mutex_unlock;
>> +		goto end;
>>  	}
>>  
>>  	if (status < 0) {
>> @@ -49,15 +49,14 @@ static int usb_read(struct intf_hdl *intfhdl, u16 addr, void *data, u8 size)
>>  		if (rtw_inc_and_chk_continual_urb_error(dvobjpriv))
>>  			adapt->bSurpriseRemoved = true;
>>  
>> -		goto mutex_unlock;
>> +		goto end;
>>  	}
>>  
>>  	rtw_reset_continual_urb_error(dvobjpriv);
>>  	memcpy(data, io_buf, size);
>>  
>> -mutex_unlock:
>> -	mutex_unlock(&dvobjpriv->usb_vendor_req_mutex);
>> -
>> +end:
>> +	kfree(io_buf);
>>  	return status;
>>  }
>>  
>> @@ -72,9 +71,10 @@ static int usb_write(struct intf_hdl *intfhdl, u16 addr, void *data, u8 size)
>>  	if (adapt->bSurpriseRemoved || adapt->pwrctrlpriv.pnp_bstop_trx)
>>  		return -EPERM;
>>  
>> -	mutex_lock(&dvobjpriv->usb_vendor_req_mutex);
>> +	io_buf = kmalloc(size, GFP_KERNEL);
>> +	if (!io_buf)
>> +		return -ENOMEM;
>>  
>> -	io_buf = dvobjpriv->usb_vendor_req_buf;
>>  	memcpy(io_buf, data, size);
>>  
>>  	status = usb_control_msg_send(udev, 0, REALTEK_USB_VENQT_CMD_REQ,
>> @@ -93,7 +93,7 @@ static int usb_write(struct intf_hdl *intfhdl, u16 addr, void *data, u8 size)
>>  		 * exist or is not enabled.
>>  		 */
>>  		adapt->bSurpriseRemoved = true;
>> -		goto mutex_unlock;
>> +		goto end;
>>  	}
>>  
>>  	if (status < 0) {
>> @@ -103,14 +103,13 @@ static int usb_write(struct intf_hdl *intfhdl, u16 addr, void *data, u8 size)
>>  		if (rtw_inc_and_chk_continual_urb_error(dvobjpriv))
>>  			adapt->bSurpriseRemoved = true;
>>  
>> -		goto mutex_unlock;
>> +		goto end;
>>  	}
>>  
>>  	rtw_reset_continual_urb_error(dvobjpriv);
>>  
>> -mutex_unlock:
>> -	mutex_unlock(&dvobjpriv->usb_vendor_req_mutex);
>> -
>> +end:
>> +	kfree(io_buf);
>>  	return status;
>>  }
>>  
>> diff --git a/drivers/staging/r8188eu/include/drv_types.h b/drivers/staging/r8188eu/include/drv_types.h
>> index 626c6273be6f..499b2bce8cbe 100644
>> --- a/drivers/staging/r8188eu/include/drv_types.h
>> +++ b/drivers/staging/r8188eu/include/drv_types.h
>> @@ -168,11 +168,6 @@ struct dvobj_priv {
>>  	int	ep_num[5]; /* endpoint number */
>>  	int	RegUsbSS;
>>  	struct semaphore usb_suspend_sema;
>> -	struct mutex  usb_vendor_req_mutex;
>> -
>> -	u8 *usb_alloc_vendor_req_buf;
>> -	u8 *usb_vendor_req_buf;
> 
> I do like removing these buffers, and I think that is all that this
> change should be doing.
> 
> thanks,
> 
> greg k-h
> 




  reply	other threads:[~2021-09-17 15:04 UTC|newest]

Thread overview: 35+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-17  7:18 [PATCH v7 00/19] staging: r8188eu: shorten and simplify calls chains Fabio M. De Francesco
2021-09-17  7:18 ` [PATCH v7 01/19] staging: r8188eu: remove usb_{read,write}_mem() Fabio M. De Francesco
2021-09-17  7:18 ` [PATCH v7 02/19] staging: r8188eu: remove the helpers of rtw_read8() Fabio M. De Francesco
2021-09-17  7:18 ` [PATCH v7 03/19] staging: r8188eu: remove the helpers of rtw_read16() Fabio M. De Francesco
2021-09-17  7:18 ` [PATCH v7 04/19] staging: r8188eu: remove the helpers of rtw_read32() Fabio M. De Francesco
2021-09-17  7:18 ` [PATCH v7 05/19] staging: r8188eu: remove the helpers of usb_write8() Fabio M. De Francesco
2021-09-17  7:18 ` [PATCH v7 06/19] staging: r8188eu: remove the helpers of usb_write16() Fabio M. De Francesco
2021-09-17  7:18 ` [PATCH v7 07/19] staging: r8188eu: remove the helpers of usb_write32() Fabio M. De Francesco
2021-09-17  7:18 ` [PATCH v7 08/19] staging: r8188eu: remove the helpers of usb_writeN() Fabio M. De Francesco
2021-09-17  7:18 ` [PATCH v7 09/19] staging: r8188eu: remove the helpers of usb_read_port() Fabio M. De Francesco
2021-09-17  7:18 ` [PATCH v7 10/19] staging: r8188eu: remove the helpers of usb_write_port() Fabio M. De Francesco
2021-09-17  7:18 ` [PATCH v7 11/19] staging: r8188eu: remove the helpers of usb_read_port_cancel() Fabio M. De Francesco
2021-09-17  7:18 ` [PATCH v7 12/19] staging: r8188eu: remove the helpers of usb_write_port_cancel() Fabio M. De Francesco
2021-09-17  7:18 ` [PATCH v7 13/19] staging: r8188eu: remove core/rtw_io.c Fabio M. De Francesco
2021-09-17  7:18 ` [PATCH v7 14/19] staging: r8188eu: remove struct _io_ops Fabio M. De Francesco
2021-09-17  7:18 ` [PATCH v7 15/19] staging: r8188eu: clean up usbctrl_vendorreq() Fabio M. De Francesco
2021-09-17 14:44   ` Greg Kroah-Hartman
2021-09-18 11:13     ` Fabio M. De Francesco
2021-09-17  7:18 ` [PATCH v7 16/19] staging: r8188eu: clean up rtw_read*() and rtw_write*() Fabio M. De Francesco
2021-09-17 14:44   ` Greg Kroah-Hartman
2021-09-17 14:45   ` Greg Kroah-Hartman
2021-09-18 11:41     ` Fabio M. De Francesco
2021-09-17  7:18 ` [PATCH v7 17/19] staging: r8188eu: shorten calls chain of rtw_read{8,16,32}() Fabio M. De Francesco
2021-09-17 14:50   ` Greg Kroah-Hartman
2021-09-17 15:01     ` David Laight
2021-09-17 15:17       ` 'Greg Kroah-Hartman'
2021-09-18 12:19     ` Fabio M. De Francesco
2021-09-17  7:18 ` [PATCH v7 18/19] staging: r8188eu: shorten calls chain of rtw_write{8,16,32,N}() Fabio M. De Francesco
2021-09-17  7:18 ` [PATCH v7 19/19] staging: r8188eu: remove shared buffer for usb requests Fabio M. De Francesco
2021-09-17 14:55   ` Greg Kroah-Hartman
2021-09-17 15:03     ` Pavel Skripkin [this message]
2021-09-17 15:06       ` Pavel Skripkin
2021-09-17 15:18       ` Greg Kroah-Hartman
2021-09-17 15:23         ` Pavel Skripkin
2021-09-17 11:07 ` [PATCH v7 00/19] staging: r8188eu: shorten and simplify calls chains Dan Carpenter

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