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Subjectpossible circular locking dependency mmap_sem/cpu_hotplug_lock.rw_sem
Hello,

After commit fc8dffd "cpu/hotplug: Convert hotplug locking to percpu rwsem"
the following lockdep splat started showing up on some systems while running
ltp's madvise06 test (right after first dirty_pages call [1]).

[1] https://github.com/linux-test-project/ltp/blob/master/testcases/kernel/syscalls/madvise/madvise06.c#L136

[21002.630252] ======================================================
[21002.637148] WARNING: possible circular locking dependency detected
[21002.644045] 4.13.0-rc3-next-20170807 #12 Not tainted
[21002.649583] ------------------------------------------------------
[21002.656492] a.out/4771 is trying to acquire lock:
[21002.661742] (cpu_hotplug_lock.rw_sem){++++++}, at: [<ffffffff812b4668>] drain_all_stock.part.35+0x18/0x140
[21002.672629]
[21002.672629] but task is already holding lock:
[21002.679137] (&mm->mmap_sem){++++++}, at: [<ffffffff8106eb35>] __do_page_fault+0x175/0x530
[21002.688371]
[21002.688371] which lock already depends on the new lock.
[21002.688371]
[21002.697505]
[21002.697505] the existing dependency chain (in reverse order) is:
[21002.705856]
[21002.705856] -> #3 (&mm->mmap_sem){++++++}:
[21002.712080] lock_acquire+0xc9/0x230
[21002.716661] __might_fault+0x70/0xa0
[21002.721241] _copy_to_user+0x23/0x70
[21002.725814] filldir+0xa7/0x110
[21002.729988] xfs_dir2_sf_getdents.isra.10+0x20c/0x2c0 [xfs]
[21002.736840] xfs_readdir+0x1fa/0x2c0 [xfs]
[21002.742042] xfs_file_readdir+0x30/0x40 [xfs]
[21002.747485] iterate_dir+0x17a/0x1a0
[21002.752057] SyS_getdents+0xb0/0x160
[21002.756638] entry_SYSCALL_64_fastpath+0x1f/0xbe
[21002.762371]
[21002.762371] -> #2 (&type->i_mutex_dir_key#3){++++++}:
[21002.769661] lock_acquire+0xc9/0x230
[21002.774239] down_read+0x51/0xb0
[21002.778429] lookup_slow+0xde/0x210
[21002.782903] walk_component+0x160/0x250
[21002.787765] link_path_walk+0x1a6/0x610
[21002.792625] path_openat+0xe4/0xd50
[21002.797100] do_filp_open+0x91/0x100
[21002.801673] file_open_name+0xf5/0x130
[21002.806429] filp_open+0x33/0x50
[21002.810620] kernel_read_file_from_path+0x39/0x80
[21002.816459] _request_firmware+0x39f/0x880
[21002.821610] request_firmware_direct+0x37/0x50
[21002.827151] request_microcode_fw+0x64/0xe0
[21002.832401] reload_store+0xf7/0x180
[21002.836974] dev_attr_store+0x18/0x30
[21002.841641] sysfs_kf_write+0x44/0x60
[21002.846318] kernfs_fop_write+0x113/0x1a0
[21002.851374] __vfs_write+0x37/0x170
[21002.855849] vfs_write+0xc7/0x1c0
[21002.860128] SyS_write+0x58/0xc0
[21002.864313] do_syscall_64+0x6c/0x1f0
[21002.868973] return_from_SYSCALL_64+0x0/0x7a
[21002.874317]
[21002.874317] -> #1 (microcode_mutex){+.+.+.}:
[21002.880748] lock_acquire+0xc9/0x230
[21002.885322] __mutex_lock+0x88/0x960
[21002.889894] mutex_lock_nested+0x1b/0x20
[21002.894854] microcode_init+0xbb/0x208
[21002.899617] do_one_initcall+0x51/0x1a9
[21002.904481] kernel_init_freeable+0x208/0x2a7
[21002.909922] kernel_init+0xe/0x104
[21002.914298] ret_from_fork+0x2a/0x40
[21002.918867]
[21002.918867] -> #0 (cpu_hotplug_lock.rw_sem){++++++}:
[21002.926058] __lock_acquire+0x153c/0x1550
[21002.931112] lock_acquire+0xc9/0x230
[21002.935688] cpus_read_lock+0x4b/0x90
[21002.940353] drain_all_stock.part.35+0x18/0x140
[21002.945987] try_charge+0x3ab/0x6e0
[21002.950460] mem_cgroup_try_charge+0x7f/0x2c0
[21002.955902] shmem_getpage_gfp+0x25f/0x1050
[21002.961149] shmem_fault+0x96/0x200
[21002.965621] __do_fault+0x1e/0xa0
[21002.969905] __handle_mm_fault+0x9c3/0xe00
[21002.975056] handle_mm_fault+0x16e/0x380
[21002.980013] __do_page_fault+0x24a/0x530
[21002.984968] do_page_fault+0x30/0x80
[21002.989537] page_fault+0x28/0x30
[21002.993812]
[21002.993812] other info that might help us debug this:
[21002.993812]
[21003.002744] Chain exists of:
[21003.002744] cpu_hotplug_lock.rw_sem --> &type->i_mutex_dir_key#3 --> &mm->mmap_sem
[21003.002744]
[21003.016238] Possible unsafe locking scenario:
[21003.016238]
[21003.022843] CPU0 CPU1
[21003.027896] ---- ----
[21003.032948] lock(&mm->mmap_sem);
[21003.036741] lock(&type->i_mutex_dir_key#3);
[21003.044419] lock(&mm->mmap_sem);
[21003.051025] lock(cpu_hotplug_lock.rw_sem);
[21003.055788]
[21003.055788] *** DEADLOCK ***
[21003.055788]
[21003.062393] 2 locks held by a.out/4771:
[21003.066675] #0: (&mm->mmap_sem){++++++}, at: [<ffffffff8106eb35>] __do_page_fault+0x175/0x530
[21003.076391] #1: (percpu_charge_mutex){+.+...}, at: [<ffffffff812b4c97>] try_charge+0x397/0x6e0
[21003.086198]
[21003.086198] stack backtrace:
[21003.091059] CPU: 6 PID: 4771 Comm: a.out Not tainted 4.13.0-rc3-next-20170807 #12
[21003.099409] Hardware name: Dell Inc. PowerEdge M520/0DW6GX, BIOS 2.4.2 02/03/2015
[21003.107766] Call Trace:
[21003.110495] dump_stack+0x85/0xc9
[21003.114190] print_circular_bug+0x1f9/0x207
[21003.118854] __lock_acquire+0x153c/0x1550
[21003.123327] lock_acquire+0xc9/0x230
[21003.127313] ? drain_all_stock.part.35+0x18/0x140
[21003.132563] cpus_read_lock+0x4b/0x90
[21003.136652] ? drain_all_stock.part.35+0x18/0x140
[21003.141900] drain_all_stock.part.35+0x18/0x140
[21003.146954] try_charge+0x3ab/0x6e0
[21003.150846] mem_cgroup_try_charge+0x7f/0x2c0
[21003.155705] shmem_getpage_gfp+0x25f/0x1050
[21003.160374] shmem_fault+0x96/0x200
[21003.164263] ? __lock_acquire+0x2fb/0x1550
[21003.168832] ? __lock_acquire+0x2fb/0x1550
[21003.173402] __do_fault+0x1e/0xa0
[21003.177097] __handle_mm_fault+0x9c3/0xe00
[21003.181669] handle_mm_fault+0x16e/0x380
[21003.186045] ? handle_mm_fault+0x49/0x380
[21003.190518] __do_page_fault+0x24a/0x530
[21003.194895] do_page_fault+0x30/0x80
[21003.198883] page_fault+0x28/0x30
[21003.202593] RIP: 0033:0x400886
[21003.205998] RSP: 002b:00007fff81d84d20 EFLAGS: 00010206
[21003.211827] RAX: 00007fc763bb7000 RBX: 0000000000000000 RCX: 0000000000001000
[21003.219789] RDX: 0000000006362000 RSI: 0000000019000000 RDI: 00007fc75d855000
[21003.227751] RBP: 00007fff81d84d50 R08: ffffffffffffffff R09: 0000000000000000
[21003.235713] R10: 00007fff81d84a30 R11: 00007fc7769445d0 R12: 0000000000400750
[21003.243681] R13: 00007fff81d84f70 R14: 0000000000000000 R15: 0000000000000000

--
Regards,
Artem

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