linux-kernel - Query: Regarding crash in n_tty_receive_buf

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Date:   Tue, 26 Dec 2017 17:58:55 +0530
From:   "Kohli, Gaurav" <gkohli@...eaurora.org>
To:     jslaby@...e.com, gregkh@...uxfoundation.org, mikey@...ling.org
Cc:     linux-kernel@...r.kernel.org
Subject: Query: Regarding crash in n_tty_receive_buf_common during boot

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
[   29.716425] LR is at n_tty_receive_buf_common+0x58/0xa3c
[   29.721882] pc : [<ffffff80085a7450>] lr : [<ffffff80085a7440>] 
pstate: 80c00145
[   29.721885] sp : ffffffc0a2b83c30
[   29.721889] x29: ffffffc0a2b83c30 x28: ffffffc093c00080
[   29.723875] x27: ffffff8009b7c0e8 x26: ffffff8009145000
[   29.729218] x25: ffffff8009cdd748 x24: ffffffc0ee040028
[   29.729225] x23: ffffffc093c7f280 x22: 0000000000000000
[   29.729231] x21: ffffffc0e3a5cf62 x20: 0000000000000032
[   29.729238] x19: 0000000000000000 x18: 0000000000000000
[   29.729245] x17: 0000000000000000 x16: 0000000000000000
[   29.729252] x15: 0000000000000000 x14: ffffffc0fb3de310
[   29.729259] x13: ffffffc0fb3de308 x12: 0000000000000000
[   29.729265] x11: ffffffc0f641aa80 x10: 0000000000000b10
[   29.729272] x9 : ffffffc0a2b83ce0 x8 : ffffffc0a2b91cf0
[   29.729279] x7 : 7aa17304d29fd900 x6 : ffffff8009bef778
[   29.729285] x5 : ffffff80085a7e24 x4 : 0000000000000001
[   29.729292] x3 : 0000000000000032 x2 : 0000000000000000
[   29.729581] x1 : 0000000000000000 x0 : 0000000000002260
[   29.732927]
[   29.732927] PC: 0xffffff80085a7410:
[   29.738025] 7410  9104e381 aa0103f6 aa0203f3 2a0303f4 b9009ba4 
f90033a1 d503201f aa1603e0
[   29.740517] 7430  b9009fbf f941af96 d0005cfa 942acb7f 91174340 
f90047a0 d2844c00 8b160000
[   29.743892] 7450  c8dffc03 f94002c2 52820000 b941eb81 4b020000 
0b030000 361800e1 528aaac1
[   29.749003] 7470  11000800 72aaaaa1 9b217c01 d360fc21 4b807c20 
51000400 52800001 6b1f001f
[   29.753967]
[   29.753967] LR: 0xffffff80085a7400:
[   29.759068] 7400  a90573fb aa0003fc aa0103f5 aa1e03e0 9104e381 
aa0103f6 aa0203f3 2a0303f4
[   29.760110] 7420  b9009ba4 f90033a1 d503201f aa1603e0 b9009fbf 
f941af96 d0005cfa 942acb7f
[   29.766051] 7440  91174340 f90047a0 d2844c00 8b160000 c8dffc03 
f94002c2 52820000 b941eb81
[   29.773012] 7460  4b020000 0b030000 361800e1 528aaac1 11000800 
72aaaaa1 9b217c01 d360fc21
[   29.779088]
[   29.779088] SP: 0xffffffc0a2b83bf0:
[   29.779092] 3bf0  085a7440 ffffff80 a2b83c30 ffffffc0 085a7450 
ffffff80 80c00145 00000000
[   29.779113] 3c10  a2b83c30 ffffffc0 085a7440 ffffff80 ffffffff 
ffffffff 09059d28 ffffff80
[   29.779134] 3c30  a2b83cd0 ffffffc0 085a7e60 ffffff80 93c00080 
ffffffc0 e3a5ce80 ffffffc0
[   29.779155] 3c50  ee040008 ffffffc0 ee040000 ffffffc0 93c7f280 
ffffffc0 ee040028 ffffffc0
[   29.779177] Process kworker/u16:10 (pid: 1216, stack limit = 
0xffffffc0a2b80000)
[   29.779181] Call trace:
[   29.779186] Exception stack(0xffffffc0a2b83a40 to 0xffffffc0a2b83b70)
[   29.779191] 3a40: 0000000000000000 0000008000000000 ffffffc0a2b83c30 
ffffff80085a7450
[   29.779195] 3a60: 0000000080c00145 ffffffc0a2b83ba0 ffffffc0a2b91180 
ffffffc0a2b91180
[   29.787281] 3a80: ffffff8009cdd6d0 ffffff80080f6ff8 ffffffc0a2b83aa0 
ffffff8008088e88
[   29.787285] 3aa0: ffffffc0a2b83ab0 ffffff8008155758 ffffffc0a2b83ae0 
ffffff8008183760
[   29.787289] 3ac0: ffffffc0a2b91180 ffffffc0f66781b0 ffffffc0f41be520 
ffffffc0f41be540
[   29.787293] 3ae0: ffffffc0a2b83b10 ffffff800818cd50 ffffffc0f41be480 
7aa17304d29fd900
[   29.795323] 3b00: 0000000000002260 0000000000000000 0000000000000000 
0000000000000032
[   29.795327] 3b20: 0000000000000001 ffffff80085a7e24 ffffff8009bef778 
7aa17304d29fd900
[   29.803361] 3b40: ffffffc0a2b91cf0 ffffffc0a2b83ce0 0000000000000b10 
ffffffc0f641aa80
[   29.803364] 3b60: 0000000000000000 ffffffc0fb3de308
[   29.808376] [<ffffff80085a7450>] n_tty_receive_buf_common+0x68/0xa3c
[   29.814893] [<ffffff80085a7e60>] n_tty_receive_buf2+0x3c/0x48
[   29.820791] [<ffffff80085ab1f8>] flush_to_ldisc+0xe4/0x124
[   29.820798] [<ffffff80080c7f78>] process_one_work+0x184/0x480
[   29.826696] [<ffffff80080c83b4>] worker_thread+0x140/0x4b4
[   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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