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    SubjectRe: [PATCH 1/2] mtd: nand: BUG_ON in case of no select_chip and cmd_ctrl
    On Tue, Jul 19, 2016 at 11:23 AM, Brian Norris
    <computersforpeace@gmail.com> wrote:
    > On Tue, Jul 19, 2016 at 08:16:11PM +0200, Boris Brezillon wrote:
    >> On Tue, 19 Jul 2016 11:11:54 -0700
    >> Andrey Smirnov <andrew.smirnov@gmail.com> wrote:
    >>
    >> > On Tue, Jul 19, 2016 at 9:22 AM, Richard Weinberger <richard@nod.at> wrote:
    >> > > Am 19.07.2016 um 18:12 schrieb Boris Brezillon:
    >> > >>>> Not sure a BUG_ON() is worst than a NULL-pointer exception ;-).
    >> > >>>
    >> > >>> When this really just triggers a NULL-pointer exception, we don't need a BUG_ON or WARN_ON at
    >> > >>> all since the kernel can tell anyway what went wrong.
    >> > >>
    >> > >> Hm, that's not entirely true, depending on your debug options you don't
    >> > >> have all the information to guess which line triggered the NULL pointer
    >> > >> exception, and this makes it harder to debug.
    >> > >> And I agree with Andrey here, it's better to complain at registration
    >> > >> time than letting the controller register all its NAND devices and
    >> > >> generate exceptions when the NAND is really used.
    >> > >>
    >> > >> BTW, I don't quite understand the rational behind BUG_ON() eradication.
    >> > >> I agree that they should not be used when the driver can recover from a
    >> > >> specific failure, but that's not really the case here (some NAND
    >> > >> controller drivers don't check nand_scan_tail() or nand_scan() return
    >> > >> code).
    >> > >
    >> > > I've been told that new code (except core code) should not BUG()/_ON().
    >> > >
    >> > >> The best solution would probably be to patch all those drivers and then
    >> > >> return an error when one of the mandatory hooks is missing, but in the
    >> > >> meantime I don't see any problem in adding BUG_ON() calls.
    >> > >
    >> > > Yes, definitely.
    >> >
    >> > I don't have any preferences as far BUG_ON/WARN_ON are concerned and
    >> > am more than happy to change one for another.
    >> >
    >> > The reason I came up with that patch is that I stumbled on that
    >> > segfault (by not providing custom select_chip() and not setting up
    >> > cmd_ctrl()) and it took me good 20 minutes to figure out the nature of
    >> > the problem, whereas, IMHO, having a BUG/WARN statement at the would
    >> > have been more self-documenting/explanatory.
    >
    > Would a normal print statement and error return have helped, like most
    > sane drivers? Like:
    >
    > if (!chip->cmd_ctrl) {
    > pr_err("No cmd_ctrl() provided\n");
    > return -EINVAL;
    > }

    Yes, that would've worked perfectly fine.

    >
    >> > What if I modify the patch to change nand_set_default's signature to
    >> > return a error code, add corresponding checking in
    >> > nand_get_flash_type()/nand_scan_ident() and replace BUG_ON with
    >> > WARN_ON? Would it be more agreeable solution?
    >
    > Sounds better to me, though I still don't see why even WARN_ON() is
    > necessary. I guess we are infected by plenty of those already anyway,
    > since I guess that's easier than writing a descriptive error message...

    It's not necessary, WARN_ON might be slightly more visible when
    skimming through dmesg, but pr_err should work as well. I'll use the
    latter in v2 then.

    Andrey

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