Hi all,
Apologies for the large Cc list, but wasn't really sure who to send this to.
I've seen this once on a Power8 box, with next-20170807.
I think it happened while I was running the memory hoptlug selftests.
cheers
[ 3532.474435] ======================================================
[ 3532.474440] WARNING: possible circular locking dependency detected
[ 3532.474446] 4.13.0-rc3-gcc6-next-20170807-g4751f76 #1 Not tainted
[ 3532.474450] ------------------------------------------------------
[ 3532.474454] ksmd/1459 is trying to acquire lock:
[ 3532.474460] (cpu_hotplug_lock.rw_sem){++++++}, at: [<c0000000002b06b0>] lru_add_drain_all+0x20/0x40
[ 3532.474476]
but task is already holding lock:
[ 3532.474480] (ksm_thread_mutex){+.+...}, at: [<c000000000330778>] ksm_scan_thread+0xd8/0x1a30
[ 3532.474493]
which lock already depends on the new lock.
[ 3532.474499]
the existing dependency chain (in reverse order) is:
[ 3532.474504]
-> #3 (ksm_thread_mutex){+.+...}:
[ 3532.474517] __mutex_lock+0x8c/0xa80
[ 3532.474522] ksm_memory_callback+0xa4/0x390
[ 3532.474529] notifier_call_chain+0xa4/0x110
[ 3532.474533] __blocking_notifier_call_chain+0x74/0xb0
[ 3532.474540] memory_notify+0x30/0x50
[ 3532.474544] __offline_pages.constprop.6+0x1c0/0xa50
[ 3532.474549] memory_subsys_offline+0x68/0xf0
[ 3532.474555] device_offline+0x104/0x140
[ 3532.474560] store_mem_state+0x178/0x190
[ 3532.474566] dev_attr_store+0x3c/0x60
[ 3532.474572] sysfs_kf_write+0x9c/0xc0
[ 3532.474576] kernfs_fop_write+0x190/0x260
[ 3532.474582] __vfs_write+0x44/0x1a0
[ 3532.474586] vfs_write+0xd4/0x240
[ 3532.474591] SyS_write+0x68/0x110
[ 3532.474597] system_call+0x58/0x6c
[ 3532.474600]
-> #2 ((memory_chain).rwsem){++++..}:
[ 3532.474609] down_read+0x44/0xa0
[ 3532.474613] __blocking_notifier_call_chain+0x58/0xb0
[ 3532.474618] memory_notify+0x30/0x50
[ 3532.474622] __offline_pages.constprop.6+0x1c0/0xa50
[ 3532.474627] memory_subsys_offline+0x68/0xf0
[ 3532.474631] device_offline+0x104/0x140
[ 3532.474636] store_mem_state+0x178/0x190
[ 3532.474641] dev_attr_store+0x3c/0x60
[ 3532.474645] sysfs_kf_write+0x9c/0xc0
[ 3532.474649] kernfs_fop_write+0x190/0x260
[ 3532.474654] __vfs_write+0x44/0x1a0
[ 3532.474659] vfs_write+0xd4/0x240
[ 3532.474663] SyS_write+0x68/0x110
[ 3532.474668] system_call+0x58/0x6c
[ 3532.474671]
-> #1 (mem_hotplug_lock.rw_sem){++++++}:
[ 3532.474680] get_online_mems+0x4c/0xd0
[ 3532.474685] kmem_cache_create+0x6c/0x2a0
[ 3532.474691] ptlock_cache_init+0x38/0x54
[ 3532.474696] start_kernel+0x2ac/0x558
[ 3532.474700] start_here_common+0x1c/0x4ac
[ 3532.474704]
-> #0 (cpu_hotplug_lock.rw_sem){++++++}:
[ 3532.474713] lock_acquire+0xec/0x2e0
[ 3532.474718] cpus_read_lock+0x4c/0xd0
[ 3532.474723] lru_add_drain_all+0x20/0x40
[ 3532.474728] ksm_scan_thread+0xba4/0x1a30
[ 3532.474734] kthread+0x164/0x1b0
[ 3532.474739] ret_from_kernel_thread+0x5c/0x74
[ 3532.474742]
other info that might help us debug this:
[ 3532.474748] Chain exists of:
cpu_hotplug_lock.rw_sem --> (memory_chain).rwsem --> ksm_thread_mutex
[ 3532.474760] Possible unsafe locking scenario:
[ 3532.474764] CPU0 CPU1
[ 3532.474768] ---- ----
[ 3532.474771] lock(ksm_thread_mutex);
[ 3532.474775] lock((memory_chain).rwsem);
[ 3532.474781] lock(ksm_thread_mutex);
[ 3532.474786] lock(cpu_hotplug_lock.rw_sem);
[ 3532.474791]
*** DEADLOCK ***
[ 3532.474797] 1 lock held by ksmd/1459:
[ 3532.474800] #0: (ksm_thread_mutex){+.+...}, at: [<c000000000330778>] ksm_scan_thread+0xd8/0x1a30
[ 3532.474810]
stack backtrace:
[ 3532.474816] CPU: 0 PID: 1459 Comm: ksmd Not tainted 4.13.0-rc3-gcc6-next-20170807-g4751f76 #1
[ 3532.474822] Call Trace:
[ 3532.474827] [c000001e54d13930] [c000000000b57c38] dump_stack+0xe8/0x160 (unreliable)
[ 3532.474835] [c000001e54d13970] [c000000000157968] print_circular_bug+0x288/0x3d0
[ 3532.474842] [c000001e54d13a10] [c00000000015b9c8] __lock_acquire+0x1858/0x1a20
[ 3532.474849] [c000001e54d13b80] [c00000000015c6fc] lock_acquire+0xec/0x2e0
[ 3532.474855] [c000001e54d13c50] [c0000000000d85cc] cpus_read_lock+0x4c/0xd0
[ 3532.474862] [c000001e54d13c80] [c0000000002b06b0] lru_add_drain_all+0x20/0x40
[ 3532.474869] [c000001e54d13ca0] [c000000000331244] ksm_scan_thread+0xba4/0x1a30
[ 3532.474876] [c000001e54d13dc0] [c00000000010b614] kthread+0x164/0x1b0
[ 3532.474883] [c000001e54d13e30] [c00000000000b6e8] ret_from_kernel_thread+0x5c/0x74
cheers
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