On 12/13/2016 08:24 PM, Michal Hocko wrote: > On Tue 13-12-16 08:57:34, Andy Lutomirski wrote: >> On Tue, Dec 13, 2016 at 2:12 AM, Michal Hocko <mho...@kernel.org> wrote: >>> [CC Andy] >>> >>> I've noticed the same >>> http://lkml.kernel.org/r/20161209142820.ga4...@dhcp22.suse.cz >>> and also concluded same as you >>> >>> On Mon 12-12-16 17:46:21, Andrey Ryabinin wrote: >>>> DEBUG_PREEMPT complains about using this_cpu_ptr() in preemptible: >>>> BUG: using smp_processor_id() in preemptible [00000000] code: >>>> iperf-300s-cs-l/277 >>>> caller is debug_smp_processor_id+0x17/0x19 >>>> CPU: 1 PID: 277 Comm: iperf-300s-cs-l Not tainted >>>> 4.9.0-rc8-00140-gcc639db #2 >>>> ffffc900003f3cf0 ffffffff8123ae6f 0000000000000001 ffffffff818181da >>>> ffffc900003f3d20 ffffffff81252f41 0000000000012de0 00000000fffffdff >>>> ffff880009328f40 ffff88000592c400 ffffc900003f3d30 ffffffff81252f6a >>>> Call Trace: >>>> [<ffffffff8123ae6f>] dump_stack+0x9a/0xd0 >>>> [<ffffffff81252f41>] check_preemption_disabled+0xdd/0xef >>>> [<ffffffff81252f6a>] debug_smp_processor_id+0x17/0x19 >>>> [<ffffffff811796df>] __vfree_deferred+0x16/0x4c >>>> [<ffffffff8117b584>] vfree_atomic+0x22/0x24 >>>> [<ffffffff81094f5d>] free_thread_stack+0xc2/0x106 >>>> [<ffffffff810951be>] put_task_stack+0x4c/0x62 >>>> [<ffffffff81095f81>] copy_process+0x7e0/0x16e8 >>>> [<ffffffff8109702d>] _do_fork+0xbb/0x2d3 >>>> [<ffffffff810465e8>] ? __do_page_fault+0x2e1/0x384 >>>> [<ffffffff8112633f>] ? trace_hardirqs_off_caller+0x12/0x24 >>>> [<ffffffff810972cb>] SyS_clone+0x19/0x1b >>>> [<ffffffff81003800>] do_syscall_64+0x143/0x173 >>>> [<ffffffff81507289>] entry_SYSCALL64_slow_path+0x25/0x25 >>>> >>>> Use raw_cpu_ptr() instead of this_cpu_ptr() to hide this warning. >>>> It's fine because llist_add() implementation is lock-less, so it works even >>>> if we adding to the list of some other cpu. schedule_work() is also >>>> preempt-safe. >>>> >>>> Reported-by: kernel test robot <ying.hu...@linux.intel.com> >>>> Signed-off-by: Andrey Ryabinin <aryabi...@virtuozzo.com> >>> >>> Acked-by: Michal Hocko <mho...@suse.com> >> >> But not quite acked by me. What happened to the vfree code that >> causes vfree_deferred to be called in a preemptable context? That >> sounds like a bug. > > Not sure I understand but the above stack points to a preemptible > context (copy_process). My stack was different and it looks preemptible as > well. > free_thread_stack calls vfree_atomic unconditionally. So I am not sure > why do you think this is a bug? > >> (This code doesn't exist in Linus' tree. What tree does this apply to.) > > Anyway, now that I am looking at Andrew's tree I can see [1] which > doesn't have this_cpu_ptr. So I am not sure where this this_cpu_ptr came > from. Maybe the previous version of the patch which has shown up in the > linux-next and Andrew has picked up [2] in the meantime. /me confused >
this_cpu_ptr() comes from the original patch http://lkml.kernel.org/r/1479474236-4139-5-git-send-email-...@lst.de Andrew picked up [2] and folded-merged it into original patch and sent it to Linus. Now it in Linus tree, commit bf22e37a641327e34681b7b6959d9646e3886 > [1] http://www.ozlabs.org/~akpm/mmotm/broken-out/mm-add-vfree_atomic.patch > [2] > http://lkml.kernel.org/r/1481553981-3856-1-git-send-email-aryabi...@virtuozzo.com >
