quoted

quoted

[   17.080644] ------------[ cut here ]------------
[   17.081342] kernel BUG at mm/pgtable-generic.c:164!
[   17.082091] Internal error: Oops - BUG: 0 [#1] PREEMPT SMP
[   17.082977] Modules linked in:
[   17.083481] CPU: 79 PID: 1 Comm: swapper/0 Tainted: G        W         5.9.0-rc2-00105-g740e72cd6717 #14
[   17.084998] Hardware name: linux,dummy-virt (DT)
[   17.085745] pstate: 60400005 (nZCv daif +PAN -UAO BTYPE=--)
[   17.086645] pc : pgtable_trans_huge_deposit+0x58/0x60
[   17.087462] lr : debug_vm_pgtable+0x4dc/0x8f0
[   17.088168] sp : ffff80001219bcf0
[   17.088710] x29: ffff80001219bcf0 x28: ffff8000114ac000
[   17.089574] x27: ffff8000114ac000 x26: 0020000000000fd3
[   17.090431] x25: 0020000081400fd3 x24: fffffe00175c12c0
[   17.091286] x23: ffff0005df04d1a8 x22: 0000f18d6e035000
[   17.092143] x21: ffff0005dd790000 x20: ffff0005df18e1a8
[   17.093003] x19: ffff0005df04cb80 x18: 0000000000000014
[   17.093859] x17: 00000000b76667d0 x16: 00000000fd4e6611
[   17.094716] x15: 0000000000000001 x14: 0000000000000002
[   17.095572] x13: 000000000055d966 x12: fffffe001755e400
[   17.096429] x11: 0000000000000008 x10: ffff0005fcb6e210
[   17.097292] x9 : ffff0005fcb6e210 x8 : 0020000081590fd3
[   17.098149] x7 : ffff0005dd71e0c0 x6 : ffff0005df18e1a8
[   17.099006] x5 : 0020000081590fd3 x4 : 0020000081590fd3
[   17.099862] x3 : ffff0005df18e1a8 x2 : fffffe00175c12c0
[   17.100718] x1 : fffffe00175c1300 x0 : 0000000000000000
[   17.101583] Call trace:
[   17.101993]  pgtable_trans_huge_deposit+0x58/0x60
[   17.102754]  do_one_initcall+0x74/0x1cc
[   17.103381]  kernel_init_freeable+0x1d0/0x238
[   17.104089]  kernel_init+0x14/0x118
[   17.104658]  ret_from_fork+0x10/0x34
[   17.105251] Code: f9000443 f9000843 f9000822 d65f03c0 (d4210000)
[   17.106303] ---[ end trace e63471e00f8c147f ]---

IIUC, this should happen even without the series right? This is

     assert_spin_locked(pmd_lockptr(mm, pmdp));

Crash does not happen without this series. A previous patch [PATCH v3 08/13]
added pgtable_trans_huge_deposit/withdraw() in pmd_advanced_tests(). arm64
does not define __HAVE_ARCH_PGTABLE_DEPOSIT and hence falls back on generic
pgtable_trans_huge_deposit() which the asserts the lock.

I fixed that by moving the pgtable deposit after adding the pmd locks 
correctly.

mm/debug_vm_pgtable/locks: Move non page table modifying test together
mm/debug_vm_pgtable/locks: Take correct page table lock
mm/debug_vm_pgtable/thp: Use page table depost/withdraw with THP

-aneesh



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