linux-kernel - Re: [PATCH] nvme-tcp: replace sg_init_marker() with sg_init

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Date:   Tue, 25 Oct 2022 11:30:16 +0200
From:   Nam Cao <namcaov@...il.com>
To:     Chaitanya Kulkarni <chaitanyak@...dia.com>
Cc:     "linux-nvme@...ts.infradead.org" <linux-nvme@...ts.infradead.org>,
        "sagi@...mberg.me" <sagi@...mberg.me>, "hch@....de" <hch@....de>,
        "axboe@...com" <axboe@...com>,
        "kbusch@...nel.org" <kbusch@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] nvme-tcp: replace sg_init_marker() with sg_init_table()

On Tue, Oct 25, 2022 at 12:58:41AM +0000, Chaitanya Kulkarni wrote:
> On 10/22/22 10:46, Nam Cao wrote:
> > In nvme_tcp_ddgst_update(), sg_init_marker() is called with an
> > uninitialized scatterlist. This is probably fine, but gcc complains:
> > 
> >    CC [M]  drivers/nvme/host/tcp.o
> > In file included from ./include/linux/dma-mapping.h:10,
> >                   from ./include/linux/skbuff.h:31,
> >                   from ./include/net/net_namespace.h:43,
> >                   from ./include/linux/netdevice.h:38,
> >                   from ./include/net/sock.h:46,
> >                   from drivers/nvme/host/tcp.c:12:
> > In function ‘sg_mark_end’,
> >      inlined from ‘sg_init_marker’ at ./include/linux/scatterlist.h:356:2,
> >      inlined from ‘nvme_tcp_ddgst_update’ at drivers/nvme/host/tcp.c:390:2:
> > ./include/linux/scatterlist.h:234:11: error: ‘sg.page_link’ is used uninitialized [-Werror=uninitialized]
> >    234 |         sg->page_link |= SG_END;
> >        |         ~~^~~~~~~~~~~
> > drivers/nvme/host/tcp.c: In function ‘nvme_tcp_ddgst_update’:
> > drivers/nvme/host/tcp.c:388:28: note: ‘sg’ declared here
> >    388 |         struct scatterlist sg;
> >        |                            ^~
> > cc1: all warnings being treated as errors
> > 
> > Use sg_init_table() instead, which basically memset the scatterlist to
> > zero first before calling sg_init_marker().
> > 
> > Signed-off-by: Nam Cao <namcaov@...il.com>
> 
> Looks good to me, can you please share what version if gcc you are
> using ? my test setup did not catch this error and I'd like to update
> with the one that can catch these errors.

It was just gcc12. But strange enough I cannot trigger this error again.
I was doing randconfig test build. Probably only a specific combination
of configs that can allow gcc to detect this...

And sorry but I was just start doing randconfig test and didn't think
about saving that .config file.

Best regards,
Nam