During a failed write to a virtual sysfs file (root fs is NFS), I got: Unable to handle kernel NULL pointer dereference at virtual address 00000020 pgd = c448bb15 [00000020] *pgd=69c9c003, *pmd=69d55003, *pte=00000000 Internal error: Oops: 207 [#1] SMP ARM Modules linked in: CPU: 0 PID: 1230 Comm: rs:main Q:Reg Not tainted 4.15.0-rc2-koelsch-01160-gd389a154c640caab-dirty #3752 Hardware name: Generic R-Car Gen2 (Flattened Device Tree) task: 4a3bb6d2 task.stack: fd0c00bd PC is at nfs_flush_incompatible+0x54/0xf8 LR is at _raw_spin_unlock+0x8/0x24 pc : [<c03bcf04>] lr : [<c074543c>] psr: 600c0013 sp : eab25e40 ip : 00000000 fp : eb9dc760 r10: ea4a1d94 r9 : 00000c20 r8 : eb9dc760 r7 : ea933840 r6 : eab24000 r5 : 00000000 r4 : 00000000 r3 : 00000000 r2 : ea933840 r1 : ea9d0900 r0 : e9d9fe40 Flags: nZCv IRQs on FIQs on Mode SVC_32 ISA ARM Segment user Control: 30c5387d Table: 6aa37440 DAC: fffffffd Process rs:main Q:Reg (pid: 1230, stack limit = 0xab6fd568) Stack: (0xeab25e40 to 0xeab26000) 5e40: 00000000 00000000 00000ab9 0000660a eaaaea00 c03b098c 00000000 00000000 5e60: eab25f10 ea4a1d94 00000167 00000547 eab24000 eab24000 c081536c c02a646c 5e80: 00000167 00000000 eab25ea0 eab25ea4 0660aab9 00000000 eaaaea00 00000ab9 5ea0: eb9dc760 c028662c 00000000 ea4a1c98 eab25f28 eaaaea00 e9c56000 eab25f10 5ec0: eab24000 00000000 b5a1c8d0 c03b0c74 00000001 00000001 0009a6f0 c02880f8 5ee0: ffffffff eaaaea00 00000002 00000000 eab25f88 00000167 eab24000 c02eb0e0 5f00: 00000167 00000000 b5a1c8d0 00000167 00000001 00000000 00000167 eab25f08 5f20: 00000001 40000002 eaaaea00 00000000 0660aab9 00000000 00000000 00000000 5f40: 00000002 00000000 00000167 eaaaea00 eab25f88 b5a1c8d0 c0207044 c02eb280 5f60: eaaaea00 b5a1c8d0 00000167 eaaaea00 eaaaea03 00000167 b5a1c8d0 c0207044 5f80: eab24000 c02eb400 0660aab9 00000000 00000167 00000167 00000000 b5a1c710 5fa0: 00000004 c0206e60 00000167 00000000 00000005 b5a1c8d0 00000167 0007d000 5fc0: 00000167 00000000 b5a1c710 00000004 b58fe91c 00069be4 000998a0 b5a1c8d0 5fe0: 00000000 b58fe4d0 b6f3c4e9 b6f3c4f0 800c0030 00000005 00000000 00000000 [<c03bcf04>] (nfs_flush_incompatible) from [<c03b098c>] (nfs_write_begin+0x50/0x208) [<c03b098c>] (nfs_write_begin) from [<c02a646c>] (generic_perform_write+0xc0/0x1ac) [<c02a646c>] (generic_perform_write) from [<c03b0c74>] (nfs_file_write+0x130/0x254) [<c03b0c74>] (nfs_file_write) from [<c02eb0e0>] (__vfs_write+0xf0/0x11c) [<c02eb0e0>] (__vfs_write) from [<c02eb280>] (vfs_write+0xb8/0x144) [<c02eb280>] (vfs_write) from [<c02eb400>] (SyS_write+0x40/0x80) [<c02eb400>] (SyS_write) from [<c0206e60>] (ret_fast_syscall+0x0/0x4c) Code: 13a04001 1a00000a e590300c e5971020 (e593c020) ---[ end trace 7dc43d92647b9bd9 ]--- Unfortunately, due to the%p hashing, I no longer know which values I can trust... Any clues? Thanks! Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html