netdev - Re: WARNING in rds_message_alloc

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Message-ID: <20181031064220.GN3974@mtr-leonro.mtl.com>
Date:   Wed, 31 Oct 2018 08:42:20 +0200
From:   Leon Romanovsky <leon@...nel.org>
To:     Santosh Shilimkar <santosh.shilimkar@...cle.com>
Cc:     syzbot <syzbot+26de17458aeda9d305d8@...kaller.appspotmail.com>,
        linux-rdma@...r.kernel.org, netdev@...r.kernel.org,
        rds-devel@....oracle.com, syzkaller-bugs@...glegroups.com,
        davem@...emloft.net, linux-kernel@...r.kernel.org
Subject: Re: WARNING in rds_message_alloc_sgs

On Tue, Oct 30, 2018 at 12:38:02PM -0700, Santosh Shilimkar wrote:
> On 10/30/2018 12:28 PM, syzbot wrote:
> > Hello,
> >
> > syzbot found the following crash on:
> >
> > HEAD commit:    6201f31a39f8 Add linux-next specific files for 20181030
> > git tree:       linux-next
> > console output: https://syzkaller.appspot.com/x/log.txt?x=1397d06d400000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=2a22859d870756c1
> > dashboard link:
> > https://syzkaller.appspot.com/bug?extid=26de17458aeda9d305d8
> > compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
> > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=10bb52eb400000
> > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=118bdfc5400000
> >
> > IMPORTANT: if you fix the bug, please add the following tag to the commit:
> > Reported-by: syzbot+26de17458aeda9d305d8@...kaller.appspotmail.com
> >
> > WARNING: CPU: 0 PID: 19789 at net/rds/message.c:316
> > rds_message_alloc_sgs+0x10c/0x160 net/rds/message.c:316
> > Kernel panic - not syncing: panic_on_warn set ...
> Looks like this kernel build has panic on warn enabled which
> triggers panic for " WARN_ON(!nr_pages)" case. Will look into
> it. Thanks !!

Please don't forget to remove user triggered WARN_ON.
https://lwn.net/Articles/769365/
"Greg Kroah-Hartman raised the problem of core kernel API code that will
use WARN_ON_ONCE() to complain about bad usage; that will not generate
the desired result if WARN_ON_ONCE() is configured to crash the machine.
He was told that the code should just call pr_warn() instead, and that
the called function should return an error in such situations. It was
generally agreed that any WARN_ON() or WARN_ON_ONCE() calls that can be
triggered from user space need to be fixed."

Thanks

>
> Regards,
> Santosh

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