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 [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 > > > >> --- > >> mm/vmalloc.c | 9 ++++++++- > >> 1 file changed, 8 insertions(+), 1 deletion(-) > >> > >> diff --git a/mm/vmalloc.c b/mm/vmalloc.c > >> index 43f0608..d8813963 100644 > >> --- a/mm/vmalloc.c > >> +++ b/mm/vmalloc.c > >> @@ -1498,7 +1498,14 @@ static void __vunmap(const void *addr, int > >> deallocate_pages) > >> > >> static inline void __vfree_deferred(const void *addr) > >> { > >> - struct vfree_deferred *p = this_cpu_ptr(&vfree_deferred); > >> + /* > >> + * Use raw_cpu_ptr() because this can be called from preemptible > >> + * context. Preemption is absolutely fine here, because llist_add() > >> + * implementation is lockless, so it works even if we adding to list > >> + * of the other cpu. > >> + * schedule_work() should be fine with this too. > >> + */ > >> + struct vfree_deferred *p = raw_cpu_ptr(&vfree_deferred); > >> > >> if (llist_add((struct llist_node *)addr, &p->list)) > >> schedule_work(&p->wq); > >> -- > >> 2.7.3 > > > > -- > > Michal Hocko > > SUSE Labs > > > > -- > Andy Lutomirski > AMA Capital Management, LLC -- Michal Hocko SUSE Labs