linux-kernel - Re: [PATCH 03/10] mpt3sas: Implement device_remove_in

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Date:   Tue, 25 Oct 2016 11:51:07 +0200
From:   Hannes Reinecke <hare@...e.de>
To:     Suganath Prabu Subramani <suganath-prabu.subramani@...adcom.com>
Cc:     JBottomley@...allels.com, jejb@...nel.org,
        Christoph Hellwig <hch@...radead.org>,
        martin.petersen@...cle.com, linux-scsi@...r.kernel.org,
        Sathya Prakash <Sathya.Prakash@...adcom.com>,
        Kashyap Desai <kashyap.desai@...adcom.com>,
        Krishnaraddi Mankani <krishnaraddi.mankani@...adcom.com>,
        linux-kernel@...r.kernel.org,
        Chaitra Basappa <chaitra.basappa@...adcom.com>,
        Sreekanth Reddy <sreekanth.reddy@...adcom.com>
Subject: Re: [PATCH 03/10] mpt3sas: Implement device_remove_in_progress check
 in IOCTL path

On 10/25/2016 11:19 AM, Suganath Prabu Subramani wrote:
> Hi Hannes,
> 
> Please give us little more info on the third comment. It ll help us to
> understand better and
> incorporate required changes.
> 
> Comment is  "Why don't you need to check for the size of the bitmap here?"
> 
> i have taken care of other two comments in this patch.
> 
>>       /* check if device is present */
>> @@ -5467,6 +5482,7 @@ _scsih_add_device(struct MPT3SAS_ADAPTER *ioc, u16 handle, u8 phy_num,
>>         sas_device = mpt3sas_get_sdev_by_addr(ioc,
>>                                         sas_address);
>>         if (sas_device) {
>> +               clear_bit(handle, ioc->pend_os_device_add);
>>                 sas_device_put(sas_device);
>>                 return -1;
>>         }
> 
> Why don't you need to check for the size of the bitmap here?
> 
> 
Thing is, you are using 'ioc->pend_os_device_add' as a bitmap to track
which devices to add.
Which in turn means that the overall number of devices you _can_ add is
restricted by the size of the bitmap.
But as you're adding devices you (might) increase the number of devices,
potentially overflowing the bitmap.
Hence the question: is it possible that you can add _more_ devices than
the bitmap can hold?
Or, to put it the other way round: Why don't you need to check the size
of the bitmap to avoid accessing an invalid bit beyond the end of the mask?

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		   Teamlead Storage & Networking
hare@...e.de			               +49 911 74053 688
SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
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