Query: Regarding crash in n_tty_receive_buf_common during boot

From: Kohli, Gaurav
Date: Tue Dec 26 2017 - 07:29:17 EST

Hi ,
We have seen lot of crashes in 4.9 during boot in n_tty_receive_buf_common, when tty->disc_data
becomes NULL, Below is the call stack for same
29.710969] PC is at n_tty_receive_buf_common+0x68/0xa3c
[ÂÂ 29.716425] LR is at n_tty_receive_buf_common+0x58/0xa3c
[ÂÂ 29.721882] pc : [<ffffff80085a7450>] lr : [<ffffff80085a7440>] pstate: 80c00145
[ÂÂ 29.721885] sp : ffffffc0a2b83c30
[ÂÂ 29.721889] x29: ffffffc0a2b83c30 x28: ffffffc093c00080
[ÂÂ 29.723875] x27: ffffff8009b7c0e8 x26: ffffff8009145000
[ÂÂ 29.729218] x25: ffffff8009cdd748 x24: ffffffc0ee040028
[ÂÂ 29.729225] x23: ffffffc093c7f280 x22: 0000000000000000
[ÂÂ 29.729231] x21: ffffffc0e3a5cf62 x20: 0000000000000032
[ÂÂ 29.729238] x19: 0000000000000000 x18: 0000000000000000
[ÂÂ 29.729245] x17: 0000000000000000 x16: 0000000000000000
[ÂÂ 29.729252] x15: 0000000000000000 x14: ffffffc0fb3de310
[ÂÂ 29.729259] x13: ffffffc0fb3de308 x12: 0000000000000000
[ÂÂ 29.729265] x11: ffffffc0f641aa80 x10: 0000000000000b10
[ÂÂ 29.729272] x9 : ffffffc0a2b83ce0 x8 : ffffffc0a2b91cf0
[ÂÂ 29.729279] x7 : 7aa17304d29fd900 x6 : ffffff8009bef778
[ÂÂ 29.729285] x5 : ffffff80085a7e24 x4 : 0000000000000001
[ÂÂ 29.729292] x3 : 0000000000000032 x2 : 0000000000000000
[ÂÂ 29.729581] x1 : 0000000000000000 x0 : 0000000000002260
[ÂÂ 29.732927]
[ÂÂ 29.732927] PC: 0xffffff80085a7410:
[ÂÂ 29.738025] 7410Â 9104e381 aa0103f6 aa0203f3 2a0303f4 b9009ba4 f90033a1 d503201f aa1603e0
[ÂÂ 29.740517] 7430Â b9009fbf f941af96 d0005cfa 942acb7f 91174340 f90047a0 d2844c00 8b160000
[ÂÂ 29.743892] 7450Â c8dffc03 f94002c2 52820000 b941eb81 4b020000 0b030000 361800e1 528aaac1
[ÂÂ 29.749003] 7470Â 11000800 72aaaaa1 9b217c01 d360fc21 4b807c20 51000400 52800001 6b1f001f
[ÂÂ 29.753967]
[ÂÂ 29.753967] LR: 0xffffff80085a7400:
[ÂÂ 29.759068] 7400Â a90573fb aa0003fc aa0103f5 aa1e03e0 9104e381 aa0103f6 aa0203f3 2a0303f4
[ÂÂ 29.760110] 7420Â b9009ba4 f90033a1 d503201f aa1603e0 b9009fbf f941af96 d0005cfa 942acb7f
[ÂÂ 29.766051] 7440Â 91174340 f90047a0 d2844c00 8b160000 c8dffc03 f94002c2 52820000 b941eb81
[ÂÂ 29.773012] 7460Â 4b020000 0b030000 361800e1 528aaac1 11000800 72aaaaa1 9b217c01 d360fc21
[ÂÂ 29.779088]
[ÂÂ 29.779088] SP: 0xffffffc0a2b83bf0:
[ÂÂ 29.779092] 3bf0Â 085a7440 ffffff80 a2b83c30 ffffffc0 085a7450 ffffff80 80c00145 00000000
[ÂÂ 29.779113] 3c10Â a2b83c30 ffffffc0 085a7440 ffffff80 ffffffff ffffffff 09059d28 ffffff80
[ÂÂ 29.779134] 3c30Â a2b83cd0 ffffffc0 085a7e60 ffffff80 93c00080 ffffffc0 e3a5ce80 ffffffc0
[ÂÂ 29.779155] 3c50Â ee040008 ffffffc0 ee040000 ffffffc0 93c7f280 ffffffc0 ee040028 ffffffc0
[ÂÂ 29.779177] Process kworker/u16:10 (pid: 1216, stack limit = 0xffffffc0a2b80000)
[ÂÂ 29.779181] Call trace:
[ÂÂ 29.779186] Exception stack(0xffffffc0a2b83a40 to 0xffffffc0a2b83b70)
[ÂÂ 29.779191] 3a40: 0000000000000000 0000008000000000 ffffffc0a2b83c30 ffffff80085a7450
[ÂÂ 29.779195] 3a60: 0000000080c00145 ffffffc0a2b83ba0 ffffffc0a2b91180 ffffffc0a2b91180
[ÂÂ 29.787281] 3a80: ffffff8009cdd6d0 ffffff80080f6ff8 ffffffc0a2b83aa0 ffffff8008088e88
[ÂÂ 29.787285] 3aa0: ffffffc0a2b83ab0 ffffff8008155758 ffffffc0a2b83ae0 ffffff8008183760
[ÂÂ 29.787289] 3ac0: ffffffc0a2b91180 ffffffc0f66781b0 ffffffc0f41be520 ffffffc0f41be540
[ÂÂ 29.787293] 3ae0: ffffffc0a2b83b10 ffffff800818cd50 ffffffc0f41be480 7aa17304d29fd900
[ÂÂ 29.795323] 3b00: 0000000000002260 0000000000000000 0000000000000000 0000000000000032
[ÂÂ 29.795327] 3b20: 0000000000000001 ffffff80085a7e24 ffffff8009bef778 7aa17304d29fd900
[ÂÂ 29.803361] 3b40: ffffffc0a2b91cf0 ffffffc0a2b83ce0 0000000000000b10 ffffffc0f641aa80
[ÂÂ 29.803364] 3b60: 0000000000000000 ffffffc0fb3de308
[ÂÂ 29.808376] [<ffffff80085a7450>] n_tty_receive_buf_common+0x68/0xa3c
[ÂÂ 29.814893] [<ffffff80085a7e60>] n_tty_receive_buf2+0x3c/0x48
[ÂÂ 29.820791] [<ffffff80085ab1f8>] flush_to_ldisc+0xe4/0x124
[ÂÂ 29.820798] [<ffffff80080c7f78>] process_one_work+0x184/0x480
[ÂÂ 29.826696] [<ffffff80080c83b4>] worker_thread+0x140/0x4b4
[ÂÂ 29.826701] [<ffffff80080cf2cc>] kthread+0xf4/0x108
I have seen some earlier patch which is fixing the same
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=71472fa9c52b1da27663c275d416d8654b905f05
but it is reverted finally in below commit:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=71472fa9c52b1da27663c275d416d8654b905f05.
Do we have any fix available for above bug, please revert me for any further information.

Regards
Gaurav

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