linux-kernel - Re: [PATCH 4.19 237/276] scsi: lpfc: avoid uninitialized variable warning

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Date:   Thu, 6 Jun 2019 09:00:42 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     Pavel Machek <pavel@...x.de>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Arnd Bergmann <arnd@...db.de>,
        James Smart <james.smart@...adcom.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Sasha Levin <sashal@...nel.org>
Subject: Re: [PATCH 4.19 237/276] scsi: lpfc: avoid uninitialized variable
 warning

On Thu, Jun 06, 2019 at 02:53:23PM +0200, Pavel Machek wrote:
> Hi!
> 
> > [ Upstream commit faf5a744f4f8d76e7c03912b5cd381ac8045f6ec ]
> > 
> > clang -Wuninitialized incorrectly sees a variable being used without
> > initialization:
> > 
> > drivers/scsi/lpfc/lpfc_nvme.c:2102:37: error: variable 'localport' is uninitialized when used here
> >       [-Werror,-Wuninitialized]
> >                 lport = (struct lpfc_nvme_lport *)localport->private;
> >                                                   ^~~~~~~~~
> > drivers/scsi/lpfc/lpfc_nvme.c:2059:38: note: initialize the variable 'localport' to silence this warning
> >         struct nvme_fc_local_port *localport;
> >                                             ^
> >                                              = NULL
> > 1 error generated.
> > 
> > This is clearly in dead code, as the condition leading up to it is always
> > false when CONFIG_NVME_FC is disabled, and the variable is always
> > initialized when nvme_fc_register_localport() got called successfully.
> > 
> > Change the preprocessor conditional to the equivalent C construct, which
> > makes the code more readable and gets rid of the warning.
> 
> Unfortunately, this missed "else" branch where the code was freeing
> the memory with kfree(cstat)... so this introduces a memory leak.
> 
> Best regards,
> 									Pavel

For the record, this is not a problem with the upstream commit (not
saying you thought that or not, I just want to be clear).

Looks like commit 4c47efc140fa ("scsi: lpfc: Move SCSI and NVME Stats to
hardware queue structures") "resolved" this by not making it an issue in
the first place. I think the simpler fix is this.

Thanks for pointing it out!

diff --git a/drivers/scsi/lpfc/lpfc_nvme.c b/drivers/scsi/lpfc/lpfc_nvme.c
index 099f70798fdd..645ffb5332b4 100644
--- a/drivers/scsi/lpfc/lpfc_nvme.c
+++ b/drivers/scsi/lpfc/lpfc_nvme.c
@@ -2477,14 +2477,14 @@ lpfc_nvme_create_localport(struct lpfc_vport *vport)
        lpfc_nvme_template.max_sgl_segments = phba->cfg_nvme_seg_cnt + 1;
        lpfc_nvme_template.max_hw_queues = phba->cfg_nvme_io_channel;
 
+       if (!IS_ENABLED(CONFIG_NVME_FC))
+               return ret;
+
        cstat = kmalloc((sizeof(struct lpfc_nvme_ctrl_stat) *
                        phba->cfg_nvme_io_channel), GFP_KERNEL);
        if (!cstat)
                return -ENOMEM;
 
-       if (!IS_ENABLED(CONFIG_NVME_FC))
-               return ret;
-
        /* localport is allocated from the stack, but the registration
         * call allocates heap memory as well as the private area.
         */