2015-01-21 14:23 GMT+01:00 Michal Hocko <mhocko@xxxxxxx>: > Hi, > I am getting tons of splats like this: > [ 187.593291] BUG: using smp_processor_id() in preemptible [00000000] code: kworker/u4:1/24 > [ 187.593293] caller is debug_smp_processor_id+0x17/0x19 > [ 187.599127] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.7.5-20140531_083030-gandalf 04/01/2014 > [ 187.601997] ffffffff8181786e ffff8800068a3d78 ffffffff8151a4b8 ffffffff81078e0e > [ 187.604373] 0000000000000000 ffff8800068a3da8 ffffffff81280ac0 ffff8800068acac8 > [ 187.606619] 00000000000029b2 ffff880007401500 00000000000000d0 ffff8800068a3db8 > [ 187.608869] Call Trace: > [ 187.609602] [<ffffffff8151a4b8>] dump_stack+0x4f/0x7c > [ 187.615881] [<ffffffff81078e0e>] ? down_trylock+0x2d/0x37 > [ 187.617468] [<ffffffff81280ac0>] check_preemption_disabled+0xe7/0xf9 > [ 187.619295] [<ffffffff81280ae9>] debug_smp_processor_id+0x17/0x19 > [ 187.621055] [<ffffffff8113b2f6>] kmem_cache_alloc_trace+0x78/0x22e > [ 187.622854] [<ffffffff81088d36>] ? do_syslog+0xb2/0x452 > [ 187.624376] [<ffffffff81088d36>] do_syslog+0xb2/0x452 > [ 187.626030] [<ffffffff811675b4>] ? __fdget_pos+0x3d/0x43 > [ 187.627557] [<ffffffff810745ac>] ? wait_woken+0x5d/0x5d > [ 187.629073] [<ffffffff811675b4>] ? __fdget_pos+0x3d/0x43 > [ 187.630611] [<ffffffff811a787b>] kmsg_read+0x2d/0x54 > [ 187.632069] [<ffffffff8119c4ff>] proc_reg_read+0x4a/0x6c > [ 187.633775] [<ffffffff8114e4d8>] vfs_read+0xa5/0x141 > [ 187.635242] [<ffffffff8114ee35>] SyS_read+0x51/0x8f > [ 187.636666] [<ffffffff81522892>] system_call_fastpath+0x12/0x17 Same here :) [1] . So actually only ARM seems affected (both armv7 and armv8) because it is the only one which uses smp_processor_id() in my_cpu_offset. [1] https://lkml.org/lkml/2015/1/20/162 Best regards, Krzysztof > > $ grep "BUG: using smp_processor_id" mmap.qcow_serial.log | wc -l > 660 > after few minutes of runtime when running the current mmotm tree > (https://git.kernel.org/cgit/linux/kernel/git/mhocko/mm.git/log/?h=since-3.18). > > The warning seems to come from this_cpu_ptr which is using my_cpu_offset > which is > #define my_cpu_offset per_cpu_offset(smp_processor_id()) > if CONFIG_DEBUG_PREEMPT > > So it matches the following code in slab_alloc_node resp. slab_free: > do { > tid = this_cpu_read(s->cpu_slab->tid); > c = this_cpu_ptr(s->cpu_slab); <<< HERE > } while (IS_ENABLED(CONFIG_PREEMPT) && unlikely(tid != c->tid)); > > This is with: > CONFIG_PREEMPT=y > CONFIG_PREEMPT_COUNT=y > CONFIG_DEBUG_PREEMPT=y > > I am not sure how to fix this but it sounds like this_cpu_ptr should > offer the same preempt expectations as other this_cpu_* functions. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>