CPU hotplug hang due to "swap: make each swap partition have oneaddress_space"

[Stephen Warren]

Shaohua,

In next-20130128, commit 174f064 "swap: make each swap partition have
one address_space" (from the mm/akpm tree) appears causes a hang/RCU
stall for me when hot-unplugging a CPU.

I'm running on a quad-core ARM system, and hot-unplugging a CPU using:

echo 0 > /sys/devices/system/cpu/cpu2/online

CONFIG_SWAP is enabled, but I don't have any swap devices activated.

If I either disable CONFIG_SWAP, or revert commit 174f064, then CPU
hotplug works fine for me.

I read through the patch and didn't see anything obvious, but I'm not
remotely familiar with the code in question.

Do you have any idea what might be wrong? Thanks.

The RCU stall kernel log is:

> [   36.152471] CPU2: shutdown
> [   57.151682] INFO: rcu_sched self-detected stall on CPU { 1}  (t=2100 jiffies g=4294966997 c=4294966996 q=1)
> [   57.164730] [<c0014658>] (unwind_backtrace+0x0/0xf8) from [<c0080c4c>] (rcu_check_callbacks+0x360/0x81c)
> [   57.177468] [<c0080c4c>] (rcu_check_callbacks+0x360/0x81c) from [<c002f4b0>] (update_process_times+0x38/0x64)
> [   57.182152] INFO: rcu_sched detected stalls on CPUs/tasks: { 1} (detected by 3, t=2103 jiffies, g=4294966997, c=4294966996, q=1)
> [   57.182154] Task dump for CPU 1:
> [   57.182162] sh              R running      0   569    568 0x00000002
> [   57.182200] [<c04d9bdc>] (__schedule+0x33c/0x6ac) from [<c000df40>] (__irq_svc+0x40/0x70)
> [   57.182211] [<c000df40>] (__irq_svc+0x40/0x70) from [<c04dae04>] (_raw_spin_unlock_irqrestore+0x28/0x50)
> [   57.182221] [<c04dae04>] (_raw_spin_unlock_irqrestore+0x28/0x50) from [<c04d4660>] (percpu_counter_hotcpu_callback+0x68/0x9c)
> [   57.182235] [<c04d4660>] (percpu_counter_hotcpu_callback+0x68/0x9c) from [<c00430f8>] (notifier_call_chain+0x44/0x84)
> [   57.182246] [<c00430f8>] (notifier_call_chain+0x44/0x84) from [<c0025fa8>] (__cpu_notify+0x28/0x44)
> [   57.182255] [<c0025fa8>] (__cpu_notify+0x28/0x44) from [<c0026104>] (cpu_notify_nofail+0x8/0x14)
> [   57.182276] [<c0026104>] (cpu_notify_nofail+0x8/0x14) from [<c04cf134>] (_cpu_down+0xf8/0x25c)
> [   57.182286] [<c04cf134>] (_cpu_down+0xf8/0x25c) from [<c04cf2bc>] (cpu_down+0x24/0x40)
> [   57.182296] [<c04cf2bc>] (cpu_down+0x24/0x40) from [<c04d0958>] (store_online+0x30/0x78)
> [   57.182317] [<c04d0958>] (store_online+0x30/0x78) from [<c027367c>] (dev_attr_store+0x18/0x24)
> [   57.182332] [<c027367c>] (dev_attr_store+0x18/0x24) from [<c0115770>] (sysfs_write_file+0x168/0x198)
> [   57.182354] [<c0115770>] (sysfs_write_file+0x168/0x198) from [<c00c4414>] (vfs_write+0x9c/0x140)
> [   57.182364] [<c00c4414>] (vfs_write+0x9c/0x140) from [<c00c46a0>] (sys_write+0x3c/0x70)
> [   57.182374] [<c00c46a0>] (sys_write+0x3c/0x70) from [<c000e2c0>] (ret_fast_syscall+0x0/0x30)
> [   57.404633] [<c002f4b0>] (update_process_times+0x38/0x64) from [<c0064798>] (tick_sched_timer+0x44/0x74)
> [   57.418340] [<c0064798>] (tick_sched_timer+0x44/0x74) from [<c0041440>] (__run_hrtimer.isra.15+0x58/0x114)
> [   57.432362] [<c0041440>] (__run_hrtimer.isra.15+0x58/0x114) from [<c0041d94>] (hrtimer_interrupt+0x100/0x290)
> [   57.446620] [<c0041d94>] (hrtimer_interrupt+0x100/0x290) from [<c0013bfc>] (twd_handler+0x2c/0x40)
> [   57.459981] [<c0013bfc>] (twd_handler+0x2c/0x40) from [<c007bdb4>] (handle_percpu_devid_irq+0x64/0x80)
> [   57.473749] [<c007bdb4>] (handle_percpu_devid_irq+0x64/0x80) from [<c007887c>] (generic_handle_irq+0x20/0x30)
> [   57.488197] [<c007887c>] (generic_handle_irq+0x20/0x30) from [<c000eb74>] (handle_IRQ+0x38/0x94)
> [   57.501559] [<c000eb74>] (handle_IRQ+0x38/0x94) from [<c00086d8>] (gic_handle_irq+0x28/0x5c)
> [   57.514610] [<c00086d8>] (gic_handle_irq+0x28/0x5c) from [<c000df40>] (__irq_svc+0x40/0x70)
> [   57.527606] Exception stack(0xed57be58 to 0xed57bea0)
> [   57.537292] be40:                                                       c06e5c50 20000113
> [   57.550216] be60: 00000000 55ec55ec 00000000 00000000 00000002 c06ea074 c06daf08 c06e5c50
> [   57.563134] be80: 00000000 00015ef8 00000000 ed57bea0 c04d4660 c04dae04 40000113 ffffffff
> [   57.576119] [<c000df40>] (__irq_svc+0x40/0x70) from [<c04dae04>] (_raw_spin_unlock_irqrestore+0x28/0x50)
> [   57.590515] [<c04dae04>] (_raw_spin_unlock_irqrestore+0x28/0x50) from [<c04d4660>] (percpu_counter_hotcpu_callback+0x68/0x9c)
> [   57.606765] [<c04d4660>] (percpu_counter_hotcpu_callback+0x68/0x9c) from [<c00430f8>] (notifier_call_chain+0x44/0x84)
> [   57.622320] [<c00430f8>] (notifier_call_chain+0x44/0x84) from [<c0025fa8>] (__cpu_notify+0x28/0x44)
> [   57.636338] [<c0025fa8>] (__cpu_notify+0x28/0x44) from [<c0026104>] (cpu_notify_nofail+0x8/0x14)
> [   57.650161] [<c0026104>] (cpu_notify_nofail+0x8/0x14) from [<c04cf134>] (_cpu_down+0xf8/0x25c)
> [   57.663859] [<c04cf134>] (_cpu_down+0xf8/0x25c) from [<c04cf2bc>] (cpu_down+0x24/0x40)
> [   57.676850] [<c04cf2bc>] (cpu_down+0x24/0x40) from [<c04d0958>] (store_online+0x30/0x78)
> [   57.690010] [<c04d0958>] (store_online+0x30/0x78) from [<c027367c>] (dev_attr_store+0x18/0x24)
> [   57.703767] [<c027367c>] (dev_attr_store+0x18/0x24) from [<c0115770>] (sysfs_write_file+0x168/0x198)
> [   57.717948] [<c0115770>] (sysfs_write_file+0x168/0x198) from [<c00c4414>] (vfs_write+0x9c/0x140)
> [   57.731866] [<c00c4414>] (vfs_write+0x9c/0x140) from [<c00c46a0>] (sys_write+0x3c/0x70)
> [   57.744841] [<c00c46a0>] (sys_write+0x3c/0x70) from [<c000e2c0>] (ret_fast_syscall+0x0/0x30)
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