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. I'm afraid "harder to trigger than you think" is not true. It is nearly trivial to trigger it now. I just tried the following on a freshly installed Fedora 21 machine: $ git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git $ cd linux $ make defconfig $ sed '/SCSI_FC_ATTRS/d;/SCSI_LOWLEVEL/d' -i .config $ make oldconfig # answer "yes" to everything $ nice make -j22 $ objdump -dr drivers/scsi/qla2xxx/qla_attr.o | grep -A10 qla2x00_get_host_fabric_name 0000000000001540 <qla2x00_get_host_fabric_name>: 1540: 55 push %rbp 1541: 48 89 e5 mov %rsp,%rbp 1544: 66 66 66 2e 0f 1f 84 data32 data32 nopw %cs:0x0(%rax,%rax,1) 154b: 00 00 00 00 00 0000000000001550 <qla2x00_fw_state_show>: 1550: 55 push %rbp 1551: 48 89 e5 mov %rsp,%rbp 1554: 53 push %rbx 1555: 48 89 d3 mov %rdx,%rbx See? I'm sure Fedora 22, 23 and 24 will also do that. -- 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
