On Fri, 2016-04-15 at 23:09 +0200, Denys Vlasenko wrote: > On 04/15/2016 09:05 PM, James Bottomley wrote: > > On Fri, 2016-04-15 at 20:56 +0200, Denys Vlasenko wrote: > > > On 04/15/2016 04:40 PM, James Bottomley wrote: > > > > On Fri, 2016-04-15 at 12:36 +0200, Denys Vlasenko wrote: > > > > > More info here: > > > > > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70646 > > > > > > > > This bug is under investigation, so I'd rather not alter code > > > > for a > > > > gcc > > > > bug until we know if we can supply options to fix it rather > > > > than > > > > changing code. > > > > > > > > > Background. The bug exists in gcc for 2 years, but it is rather > > > hard to trigger, so nobody noticed. > > > > We know this ... linux-scsi is on the cc for the other thread on > > this. > > > > > Unfortunately for kernel, these two commits landed in Linus tree > > > in March 16 and 17: > > > > > > > > > On 04/13/2016 05:36 AM, Josh Poimboeuf wrote: > > > > It occurs with the combination of the following two recent > > > > commits: > > > > > > > > - bc27fb68aaad ("include/uapi/linux/byteorder, swab: force > > > > inlining > > > > of some byteswap operations") > > > > - ef3fb2422ffe ("scsi: fc: use get/put_unaligned64 for wwn > > > > access") > > > > > > > > > and now *many* users of qla2x00 and new-ish gcc are going to > > > very much notice it, as their kernels will start crashing > > > reliably. > > > > > > The commits can be reverted, sure, but they per se do not contain > > > anything unusual. They, together with not very typical construct > > > in qla2x00_get_host_fabric_name, one > > > which boils down to "swab64p(constant_array_of_8_bytes)", > > > just happen to nudge gcc in a right way to finally trigger the > > > bug. > > > > > > So I came with another idea how to forestall the imminent deluge > > > of > > > qla2x00 oops reports - this patch. > > > > There are actually a raft of checkers that run the upstream code > > which > > aren't seeing any problem; likely because the code is harder to > > trigger > > than you think. So, lets wait until the resolution of the other > > thread > > before we panic, especially since we're only at -rc3. > > I'm not panicking, James. > > By sending a workaround, I just want to make sure that *other people* > won't be forced to fix up a problem which surfaced because of *my* > patch. Look, if gcc really proves to be intractable, I think what should happen is revert the triggering patch, which is commit e3bde9568d992c5f985e6e30731a5f9f9bef7b13 Author: Denys Vlasenko <dvlasenk@xxxxxxxxxx> Date: Thu Mar 17 14:22:47 2016 -0700 include/linux/unaligned: force inlining of byteswap operations But, as I've said a couple of times now, there are no bug reports from the testers about qla2xxx (yet) so we can afford to wait a bit and see if there's some other resolution that doesn't involve changing kernel code to work around a local gcc bug. James -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
