linux-kernel - Re: [PATCH -tip][SCSI] scsi: scsi_transport_iscsi.c initialize the variable before it get used

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Date:	Tue, 26 May 2009 21:30:05 +0530
From:	Jaswinder Singh Rajput <jaswinder@...nel.org>
To:	James Bottomley <James.Bottomley@...senPartnership.com>
Cc:	linux-scsi <linux-scsi@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>, x86 maintainers <x86@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -tip][SCSI] scsi: scsi_transport_iscsi.c initialize the
 variable before it get used

Hello James,

On Tue, 2009-05-26 at 10:28 -0500, James Bottomley wrote:
> On Tue, 2009-05-26 at 20:49 +0530, Jaswinder Singh Rajput wrote:
> > I am watching this problem from long time in -tip.
> > 
> > Subject: [PATCH] scsi: scsi_transport_iscsi.c initialize the variable before it get used
> > 
> > In some cases, err will be used uninitialized.
> 
> What cases?  A simple theoretical analysis shows that this variable is
> always set.
> 

Ok lets takes your tree:

http://git.kernel.org/?p=linux/kernel/git/jejb/scsi-misc-2.6.git;a=blob;f=drivers/scsi/scsi_transport_iscsi.c;hb=10eb0f013c63c71c82ede77945a5f390c10cfda6


672 int iscsi_add_session(struct iscsi_cls_session *session, unsigned int target_id)
673 {
674         struct Scsi_Host *shost = iscsi_session_to_shost(session);
675         struct iscsi_cls_host *ihost;
676         unsigned long flags;
677         unsigned int id = target_id;
678         int err;
679
680         ihost = shost->shost_data;
681         session->sid = atomic_add_return(1, &iscsi_session_nr);
682
683         if (id == ISCSI_MAX_TARGET) {
684                 for (id = 0; id < ISCSI_MAX_TARGET; id++) {
685                         err = device_for_each_child(&shost->shost_gendev, &id,
686                                                     iscsi_get_next_target_id);
687                         if (!err)
688                                 break;
689                 }
690
691                 if (id == ISCSI_MAX_TARGET) {
692                         iscsi_cls_session_printk(KERN_ERR, session,
693                                                  "Too many iscsi targets. Max "
694                                                  "number of targets is %d.\n",
695                                                  ISCSI_MAX_TARGET - 1);
696                         goto release_host;
697                 }
698         }
699         session->target_id = id;
700
701         dev_set_name(&session->dev, "session%u", session->sid);
702         err = device_add(&session->dev);
703         if (err) {
704                 iscsi_cls_session_printk(KERN_ERR, session,
705                                          "could not register session's dev\n");
706                 goto release_host;
707         }
708         transport_register_device(&session->dev);
709
710         spin_lock_irqsave(&sesslock, flags);
711         list_add(&session->sess_list, &sesslist);
712         spin_unlock_irqrestore(&sesslock, flags);
713
714         iscsi_session_event(session, ISCSI_KEVENT_CREATE_SESSION);
715         return 0;
716
717 release_host:
718         scsi_host_put(shost);
719         return err;
720 }

You are right but compiler is confused and giving warning like this :

1. do not go inside :
684                 for (id = 0; id < ISCSI_MAX_TARGET; id++) {

2. and then choose path :
696                         goto release_host;

then we return err uninitialized ;-)

> >  CC      drivers/scsi/scsi_transport_iscsi.o
> > drivers/scsi/scsi_transport_iscsi.c: In function ‘iscsi_add_session’:
> > drivers/scsi/scsi_transport_iscsi.c:678: warning: ‘err’ may be used
> > uninitialized in this function
> 
> My version of gcc (4.3.3) correctly sees that the variable cannot be
> uninitialised ... what version are you using?
> 
> If it's a popular version, we can always do the uninitialised_var()
> thing, but if it's just a non-standard compiler, I'd rather not mess up
> the source code to please gcc.
> 

gcc version 4.3.2 20081105 (Red Hat 4.3.2-7) (GCC) 

--
JSR

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