[PATCH v2 2/3] mm, thp: fix possible circular locking dependency caused by sum_vm_event()
From: Ebru Akagunduz
Date: Fri May 27 2016 - 03:59:54 EST
Nested circular locking dependency detected by kernel robot (udevadm).
udevadm/221 is trying to acquire lock:
(&mm->mmap_sem){++++++}, at: [<ffffffff81262543>] __might_fault+0x83/0x150
but task is already holding lock:
(s_active#12){++++.+}, at: [<ffffffff813315ee>] kernfs_fop_write+0x8e/0x250
which lock already depends on the new lock.
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
lock(s_active);
lock(cpu_hotplug.lock);
lock(s_active);
lock(&mm->mmap_sem);
the existing dependency chain (in reverse order) is:
-> #2 (s_active#12){++++.+}:
[<ffffffff8117da2c>] lock_acquire+0xac/0x180
[<ffffffff8132f50a>] __kernfs_remove+0x2da/0x410
[<ffffffff81330630>] kernfs_remove_by_name_ns+0x40/0x90
[<ffffffff813339fb>] sysfs_remove_file_ns+0x2b/0x70
[<ffffffff81ba8a16>] device_del+0x166/0x320
[<ffffffff81ba943c>] device_destroy+0x3c/0x50
[<ffffffff8105aa61>] cpuid_class_cpu_callback+0x51/0x70
[<ffffffff81131ce9>] notifier_call_chain+0x59/0x190
[<ffffffff81132749>] __raw_notifier_call_chain+0x9/0x10
[<ffffffff810fe6b0>] __cpu_notify+0x40/0x90
[<ffffffff810fe890>] cpu_notify_nofail+0x10/0x30
[<ffffffff810fe8d7>] notify_dead+0x27/0x1e0
[<ffffffff810fe273>] cpuhp_down_callbacks+0x93/0x190
[<ffffffff82096062>] _cpu_down+0xc2/0x1e0
[<ffffffff810ff727>] do_cpu_down+0x37/0x50
[<ffffffff8110003b>] cpu_down+0xb/0x10
[<ffffffff81038e4d>] _debug_hotplug_cpu+0x7d/0xd0
[<ffffffff8435d6bb>] debug_hotplug_cpu+0xd/0x11
[<ffffffff84352426>] do_one_initcall+0x138/0x1cf
[<ffffffff8435270a>] kernel_init_freeable+0x24d/0x2de
[<ffffffff8209533a>] kernel_init+0xa/0x120
[<ffffffff820a7972>] ret_from_fork+0x22/0x50
-> #1 (cpu_hotplug.lock#2){+.+.+.}:
[<ffffffff8117da2c>] lock_acquire+0xac/0x180
[<ffffffff820a20d1>] mutex_lock_nested+0x71/0x4c0
[<ffffffff810ff526>] get_online_cpus+0x66/0x80
[<ffffffff81246fb3>] sum_vm_event+0x23/0x1b0
[<ffffffff81293768>] collapse_huge_page+0x118/0x10b0
[<ffffffff81294c5d>] khugepaged+0x55d/0xe80
[<ffffffff81130304>] kthread+0x134/0x1a0
[<ffffffff820a7972>] ret_from_fork+0x22/0x50
-> #0 (&mm->mmap_sem){++++++}:
[<ffffffff8117bf61>] __lock_acquire+0x2861/0x31f0
[<ffffffff8117da2c>] lock_acquire+0xac/0x180
[<ffffffff8126257e>] __might_fault+0xbe/0x150
[<ffffffff8133160f>] kernfs_fop_write+0xaf/0x250
[<ffffffff812a8933>] __vfs_write+0x43/0x1a0
[<ffffffff812a8d3a>] vfs_write+0xda/0x240
[<ffffffff812a8f84>] SyS_write+0x44/0xa0
[<ffffffff820a773c>] entry_SYSCALL_64_fastpath+0x1f/0xbd
This patch moves sum_vm_event() before taking down_write(&mm->mmap_sem)
to solve dependency lock.
Signed-off-by: Ebru Akagunduz <ebru.akagunduz@xxxxxxxxx>
---
Changes in v2:
- Nothing changed
mm/huge_memory.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 5e71d7a..9adf1c7 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2452,6 +2452,9 @@ static void collapse_huge_page(struct mm_struct *mm,
goto out_nolock;
}
+ swap = get_mm_counter(mm, MM_SWAPENTS);
+ curr_allocstall = sum_vm_event(ALLOCSTALL);
+
/*
* Prevent all access to pagetables with the exception of
* gup_fast later hanlded by the ptep_clear_flush and the VM
@@ -2484,8 +2487,6 @@ static void collapse_huge_page(struct mm_struct *mm,
goto out;
}
- swap = get_mm_counter(mm, MM_SWAPENTS);
- curr_allocstall = sum_vm_event(ALLOCSTALL);
/*
* Don't perform swapin readahead when the system is under pressure,
* to avoid unnecessary resource consumption.
--
1.9.1