WARNING in con_is_bound

[Jens Remus <jremus@linux.ibm.com>]

Hello!

Our CI on s390x constantly triggers the following warning in function con_is_bound() when reading the SysFS attribute /sys/class/vtconsole/vtcon0/bind.
I verified this to be the case since WARN_CONSOLE_UNLOCKED() was introduced in function con_is_bound() with commit ddde3c18b700 ("vt: More locking checks"), which has recently been merged into Linus' master branch.


From CI with recent Linus' master branch built with arch/s390/configs/defconfig. dump2tar is a utility we use to collect the whole SysFS as tar archive for problem determination.

WARNING: CPU: 7 PID: 47758 at drivers/tty/vt/vt.c:3825 con_is_bound+0x8e/0x98
Kernel panic - not syncing: panic_on_warn set ...
CPU: 7 PID: 47758 Comm: dump2tar Tainted: G           OE     5.3.0-20190715.rc0.git0.1d039859330b.301.fc30.s390x+git #1
Hardware name: IBM ... (z/VM 7.1.0)
Call Trace:
([<00000000291b7b46>] show_stack+0x8e/0xd0)
 [<0000000029b82242>] dump_stack+0x7a/0xa8
 [<00000000291e9aea>] panic+0x112/0x308
 [<00000000291e991a>] __warn+0xc2/0x118
 [<0000000029b81312>] report_bug+0xfa/0x158
 [<00000000291a534c>] do_report_trap+0xc4/0xe0
 [<00000000291a5522>] illegal_op+0x13a/0x150
 [<0000000029ba2a1c>] pgm_check_handler+0x1c8/0x220
 [<0000000029877626>] con_is_bound+0x8e/0x98
([<000000008fed2820>] 0x8fed2820)
 [<0000000029878502>] show_bind+0x32/0x58
 [<00000000298f46f4>] dev_attr_show+0x2c/0x70
 [<00000000294d57ac>] sysfs_kf_seq_show+0xac/0x158
 [<00000000294565a0>] seq_read+0xe0/0x478
 [<000000002942774c>] vfs_read+0x94/0x150
 [<0000000029427b10>] ksys_read+0x68/0xf8
 [<0000000029ba2624>] system_call+0xd8/0x2c8


From verification with Kernel based on commit ddde3c18b700 ("vt: More locking checks") built with arch/s390/configs/performance_defconfig. I used cat /sys/class/vtconsole/vtcon0/bind to trigger the warning.

WARNING: CPU: 0 PID: 923 at drivers/tty/vt/vt.c:3825 con_is_bound+0x8e/0x98
Modules linked in: ...
CPU: 0 PID: 923 Comm: cat Not tainted 5.2.0-rc4-00004-gddde3c18b700 #2
Hardware name: IBM 3906 M03 703 (z/VM 7.1.0)
Krnl PSW : 0704c00180000000 0000000041418856 (con_is_bound+0x8e/0x98)
           R:0 T:1 IO:1 EX:1 Key:0 M:1 W:0 P:0 AS:3 CC:0 PM:0 RI:0 EA:3
Krnl GPRS: 000000003d6a4000 0000000000000000 0000000000000000 0000000041b3cd88
           000000007aba3000 0000000041493378 000000007b52b428 0000000000000000
           000003e000abfef8 0000000078dc6540 0000000041bbe310 0000000041bbbf10
           000000007ac4a000 000000007b52b440 0000000041418842 000003e000abfca8
Krnl Code: 000000004141884c: 1612                or      %r1,%r2
           000000004141884e: a774ffd5            brc     7,414187f8
          #0000000041418852: a7f40001            brc     15,41418854
          >0000000041418856: a7f4ffd1            brc     15,414187f8
           000000004141885a: 0707                bcr     0,%r7
           000000004141885c: 0707                bcr     0,%r7
           000000004141885e: 0707                bcr     0,%r7
           0000000041418860: c00400000000        brcl    0,41418860
Call Trace:
([<000003e000abfca0>] 0x3e000abfca0)
 [<0000000041419732>] show_bind+0x32/0x58
 [<00000000414933a8>] dev_attr_show+0x30/0x70
 [<00000000410798e8>] sysfs_kf_seq_show+0xb0/0x158
 [<0000000040ffa95c>] seq_read+0xe4/0x478
 [<0000000040fcbe84>] vfs_read+0x94/0x150
 [<0000000040fcc248>] ksys_read+0x68/0xf8
 [<0000000041733530>] system_call+0xdc/0x2c8
Last Breaking-Event-Address:
 [<0000000041418852>] con_is_bound+0x8a/0x98
---[ end trace 80e05e05ec2ee660 ]---


Thanks and regards,
Jens Remus
-- 
Linux on Z and z/VSE Development & Service (D3229)
IBM Systems & Technology Group, Pure Systems & Modular Software Development

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