Commits
Michal Hocko committed f64ac5e6e30
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
NMI watchdog: BUG: soft lockup - CPU#11 stuck for 23s! [kworker/u641:3:832]
[...]
Workqueue: events_unbound async_run_entry_fn
task: ffff881809270f40 ti: ffff881809274000 task.ti: ffff881809274000
RIP: _raw_spin_unlock_irqrestore+0x11/0x20
RSP: 0018:ffff881809277b10 EFLAGS: 00000286
[...]
Call Trace:
sparse_add_one_section+0x13d/0x18e
__add_pages+0x10a/0x1d0
arch_add_memory+0x4a/0xc0
devm_memremap_pages+0x29d/0x430
pmem_attach_disk+0x2fd/0x3f0 [nd_pmem]
nvdimm_bus_probe+0x64/0x110 [libnvdimm]
driver_probe_device+0x1f7/0x420
bus_for_each_drv+0x52/0x80
__device_attach+0xb0/0x130
bus_probe_device+0x87/0xa0
device_add+0x3fc/0x5f0
nd_async_device_register+0xe/0x40 [libnvdimm]
async_run_entry_fn+0x43/0x150
process_one_work+0x14e/0x410
worker_thread+0x116/0x490
kthread+0xc7/0xe0
ret_from_fork+0x3f/0x70
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@kernel.org
Signed-off-by: Michal Hocko <mhocko@suse.com>
Reported-by: Johannes Thumshirn <jthumshirn@suse.de>
Tested-by: Johannes Thumshirn <jthumshirn@suse.de>
Cc: Dan Williams <dan.j.williams@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>