Messages in this thread | | | From | Andrey Smirnov <> | Date | Tue, 19 Jul 2016 11:36:01 -0700 | Subject | Re: [PATCH 1/2] mtd: nand: BUG_ON in case of no select_chip and cmd_ctrl |
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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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