linux-kernel - Re: [PATCH 04/20] [SCSI] mpt3sas: Remove redundancy code while freeing the controller resources.

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Date:	Mon, 15 Jun 2015 12:48:05 +0200
From:	Johannes Thumshirn <jthumshirn@...e.de>
To:	Sreekanth Reddy <sreekanth.reddy@...gotech.com>
Cc:	"jejb@...nel.org" <jejb@...nel.org>,
	Christoph Hellwig <hch@...radead.org>,
	"Martin K. Petersen" <martin.petersen@...cle.com>,
	"linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
	"James E.J. Bottomley" <JBottomley@...allels.com>,
	Sathya Prakash <Sathya.Prakash@...gotech.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 04/20] [SCSI] mpt3sas: Remove redundancy code while
 freeing the controller resources.

On Mon, Jun 15, 2015 at 03:56:56PM +0530, Sreekanth Reddy wrote:
> On Fri, Jun 12, 2015 at 6:10 PM, Johannes Thumshirn <jthumshirn@...e.de> wrote:
> > On Fri, Jun 12, 2015 at 05:48:56PM +0530, Sreekanth Reddy wrote:
> >> On Fri, Jun 12, 2015 at 4:58 PM, Johannes Thumshirn <jthumshirn@...e.de> wrote:
> >> > On Fri, Jun 12, 2015 at 03:12:16PM +0530, Sreekanth Reddy wrote:
> >> >> Removed the redundancy code while freeing the controller resources.
> >> >>
> >> >> Signed-off-by: Sreekanth Reddy <Sreekanth.Reddy@...gotech.com>
> >> >> ---
> >> >>  drivers/scsi/mpt3sas/mpt3sas_base.c | 57 +++++++++++++++++++++----------------
> > [...]
> >> >> +     _base_free_irq(ioc);
> >> >> +     _base_disable_msix(ioc);
> >> >> +
> >> >> +     if (ioc->msix96_vector)
> >> >> +             kfree(ioc->replyPostRegisterIndex);
> >> >
> >> > kfree() already checks for zero or a NULL pointer.
> >>
> >> Sorry Johannes, I didn't get you. If I understand this correctly, you
> >> are suggesting to check for NULL pointer before calling kree() API as
> >> shown below,
> >>
> >> if (ioc->msix96_vector && (ioc->replyPostRegisterIndex != NULL))
> >>         kfree(ioc->replyPostRegisterIndex);
> >
> > Correct me if I'm wrong, but I thought you don't need the if
> > (ioc->msix96_vector) before the kfree(). ioc->replyPostRegisterIndex should be
> > NULL if ioc->msix96_vector is 0, as far as I can see.
> >
> > In _scsih_probe() you have:
> > shost = scsi_host_alloc(&scsih_driver_template,
> >             sizeof(struct MPT3SAS_ADAPTER));
> > if (!shost)
> >            return -ENODEV;
> >
> > /* init local params */
> > ioc = shost_priv(shost);
> >
> > and scsi_host_alloc() does a kzalloc() for shost.
> >
> > so ioc->replyPortRegisterIndex is NULL.
> >
> > Or am I thinking wrong here?
> 
> Yes, ioc->replyPostRegisterIndex will be NULL if ioc->msix96_vector is 0,
> We have added this checks as a precautionary. since calling this
> function (i.e kfree()) on memory not previously allocated with
> kmalloc(), or on memory which has already been freed, may results in
> very bad things, such as freeing memory belonging to another part of
> the kernel.
>

OK, then please leave it in.

> >
> >>
> >> Regards,
> >> Sreekanth
> >
> > --
> > Johannes Thumshirn                                       Storage
> > jthumshirn@...e.de                             +49 911 74053 689
> > SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
> > GF: F. Imendörffer, J. Smithard, J. Guild, D. Upmanyu, G. Norton
> > HRB 21284 (AG Nürnberg)
> 
> 
> 
> -- 
> 
> Regards,
> Sreekanth

-- 
Johannes Thumshirn                                       Storage
jthumshirn@...e.de                             +49 911 74053 689
SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: F. Imendörffer, J. Smithard, J. Guild, D. Upmanyu, G. Norton
HRB 21284 (AG Nürnberg)
--
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