From: Michal Hocko <mhocko@xxxxxxxx> Subject: mm, memory_hotplug: add scheduling point to __add_pages Patch series "mm, memory_hotplug: fix few soft lockups in memory hotadd". Johannes has noticed few soft lockups when adding a large nvdimm device. All of them were caused by a long loop without any explicit cond_resched which is a problem for !PREEMPT kernels. The fix is quite straightforward. Just make sure that cond_resched gets called from time to time. This patch (of 3): __add_pages gets a pfn range to add and there is no upper bound for a single call. This is usually a memory block aligned size for the regular memory hotplug - smaller sizes are usual for memory balloning drivers, or the whole NUMA node for physical memory online. There is no explicit scheduling point in that code path though. This can lead to long latencies while __add_pages is executed and we have even seen a soft lockup report during nvdimm initialization with !PREEMPT kernel [ 33.588806] NMI watchdog: BUG: soft lockup - CPU#11 stuck for 23s! [kworker/u641:3:832] [...] [ 33.588875] Workqueue: events_unbound async_run_entry_fn [ 33.588876] task: ffff881809270f40 ti: ffff881809274000 task.ti: ffff881809274000 [ 33.588878] RIP: 0010:[<ffffffff81608c01>] [<ffffffff81608c01>] _raw_spin_unlock_irqrestore+0x11/0x20 [ 33.588883] RSP: 0018:ffff881809277b10 EFLAGS: 00000286 [...] [ 33.588900] Call Trace: [ 33.588906] [<ffffffff81603a45>] sparse_add_one_section+0x13d/0x18e [ 33.588909] [<ffffffff815fde8a>] __add_pages+0x10a/0x1d0 [ 33.588916] [<ffffffff810634ca>] arch_add_memory+0x4a/0xc0 [ 33.588920] [<ffffffff8118b22d>] devm_memremap_pages+0x29d/0x430 [ 33.588931] [<ffffffffa042e50d>] pmem_attach_disk+0x2fd/0x3f0 [nd_pmem] [ 33.589001] [<ffffffffa14ad984>] nvdimm_bus_probe+0x64/0x110 [libnvdimm] [ 33.589008] [<ffffffff8146a337>] driver_probe_device+0x1f7/0x420 [ 33.589012] [<ffffffff814682f2>] bus_for_each_drv+0x52/0x80 [ 33.589014] [<ffffffff8146a020>] __device_attach+0xb0/0x130 [ 33.589017] [<ffffffff81469447>] bus_probe_device+0x87/0xa0 [ 33.589020] [<ffffffff8146741c>] device_add+0x3fc/0x5f0 [ 33.589029] [<ffffffffa14acffe>] nd_async_device_register+0xe/0x40 [libnvdimm] [ 33.589047] [<ffffffff8109e1c3>] async_run_entry_fn+0x43/0x150 [ 33.589073] [<ffffffff8109594e>] process_one_work+0x14e/0x410 [ 33.589086] [<ffffffff810961a6>] worker_thread+0x116/0x490 [ 33.589089] [<ffffffff8109b677>] kthread+0xc7/0xe0 [ 33.589119] [<ffffffff816094bf>] ret_from_fork+0x3f/0x70 [ 33.590756] DWARF2 unwinder stuck at ret_from_fork+0x3f/0x70 Fix this by adding cond_resched once per each memory section in the given pfn range. Each section is constant amount of work which itself is not too expensive but many of them will just add up. Link: http://lkml.kernel.org/r/20170918121410.24466-2-mhocko@xxxxxxxxxx Signed-off-by: Michal Hocko <mhocko@xxxxxxxx> Reported-by: Johannes Thumshirn <jthumshirn@xxxxxxx> Tested-by: Johannes Thumshirn <jthumshirn@xxxxxxx> Cc: Dan Williams <dan.j.williams@xxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/memory_hotplug.c | 1 + 1 file changed, 1 insertion(+) diff -puN mm/memory_hotplug.c~mm-memory_hotplug-add-scheduling-point-to-__add_pages mm/memory_hotplug.c --- a/mm/memory_hotplug.c~mm-memory_hotplug-add-scheduling-point-to-__add_pages +++ a/mm/memory_hotplug.c @@ -328,6 +328,7 @@ int __ref __add_pages(int nid, unsigned if (err && (err != -EEXIST)) break; err = 0; + cond_resched(); } vmemmap_populate_print_last(); out: _ -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
