linux-kernel - Re: scsi: BUG in scsi_init

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Date:   Tue, 31 Jan 2017 11:06:29 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Johannes Thumshirn <jthumshirn@...e.de>
Cc:     jejb@...ux.vnet.ibm.com,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        linux-scsi <linux-scsi@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        syzkaller <syzkaller@...glegroups.com>,
        Hannes Reinecke <hare@...e.de>
Subject: Re: scsi: BUG in scsi_init_io

On Tue, Jan 31, 2017 at 10:58 AM, Johannes Thumshirn <jthumshirn@...e.de> wrote:
>
> [...]
>
>> Please-please-please, let's not use WARN for something that is not a
>> kernel bug and is user-triggerable. This makes it impossible to
>> automate kernel testing and requires hiring an army of people doing
>> mechanical job of sorting out WARNING reports into kernel-bugs and
>> non-kernel-bugs.
>> If the message is absolutely necessary (while kernel does not
>> generally explain every EINVAL on console), the following will do:
>>
>>       if (!blk_rq_nr_phys_segments(rq)) {
>>               pr_err("you are doing something wrong\n");
>>               return -EINVAL;
>>       }
>
> Yes I understand that. OTOH having the WARN helps you finding the caller because
> of to the stack trace. But arguably that could be accomplished with function
> graph tracing as well. I'll re-send a v2 as a proper patch.


Thank you very much.
Stack trace can be done with dump_stack() if necessary, e.g.

               pr_err("you are doing something wrong here:\n");
               dump_stack();