* [LTP] [bug] hard lockup on read of /sys/kernel/debug/regmap/dummy-csw@7e200000/registers
[not found] <2122098936.3785405.1570402459950.JavaMail.zimbra@redhat.com>
@ 2019-10-06 23:20 ` Jan Stancek
0 siblings, 0 replies; only message in thread
From: Jan Stancek @ 2019-10-06 23:20 UTC (permalink / raw)
To: ltp
Hi,
This started with recent CKI reports of LTP read_all_sys sometimes running into
hard lockups [1] on arm64 system [2].
It comes down to reading /sys/kernel/debug/regmap/dummy-csw@7e200000/registers,
which completely locks up the system. Can be reproduced with 5.3.0, 5.3.4
upstream kernels and also Fedora's 5.0.9-301.fc30.aarch64.
# cat /sys/kernel/debug/regmap/dummy-csw@7e200000/name
nodev
# cat /sys/kernel/debug/regmap/dummy-csw@7e200000/range
0-ffc
# cat /sys/kernel/debug/regmap/dummy-csw@7e200000/registers
<hangs>
Adding extra output to regmap_read_debugfs [3] shows [4]: first 3 iterations
of for loop complete OK, but 4th one never returns from regmap_read(),
and system becomes unresponsive (ssh, serial console, ping).
Regards,
Jan
[1]
[17552.810666] LTP: starting read_all_sys (read_all -d /sys -q -r 10 -e /sys/power/wakeup_count)
[17626.529140] rcu: INFO: rcu_sched detected stalls on CPUs/tasks:
[17626.535046] rcu: 1-...0: (0 ticks this GP) idle=05a/1/0x4000000000000000 softirq=746561/746561 fqs=2042
[17626.544568] (detected by 7, t=6003 jiffies, g=1380217, q=747)
[17626.550372] Task dump for CPU 1:
[17626.553582] read_all R running task 0 12363 12356 0x00000202
[17626.560598] Call trace:
[17626.563037] __switch_to+0x104/0x1f8
[17626.566596] kmem_cache_alloc_trace+0x1f0/0x278
[17626.571104] debugfs_file_get+0x64/0x108
[17626.575007] 0x0
[2]
apm-mustang-b0-03
description: System
product: APM X-Gene Mustang board
vendor: AmpereComputing(R)
version: 1.0
serial: 3PCC-A00000
width: 64 bits
capabilities: smbios-3.1.1 dmi-3.1.1 smp
configuration: boot=normal chassis=server family=eMAG sku=EV-883208-X1-MB2-2 uuid=00020003-0004-0005-0006-0001730237A0
*-core
description: Motherboard
product: Mustang
vendor: AmpereComputing(R)
physical id: 0
version: 1.0
serial: 3PCC-A00000
slot: Part Component
*-firmware
description: BIOS
vendor: American Megatrends Inc.
physical id: 0
version: 0ACDY027
date: 12/12/2018
size: 64KiB
capacity: 13MiB
capabilities: pci upgrade cdboot bootselect acpi uefi
*-cpu:0
description: CPU
product: ARM (883208X1-SA24T)
vendor: AmpereComputing(R)
physical id: 4
bus info: cpu@0
version: B0
serial: 883208X1-SA24T
slot: eMAG
size: 2400MHz
capacity: 2400MHz
clock: 2400MHz
capabilities: lm
configuration: cores=8 enabledcores=8
*-memory
description: System Memory
physical id: 1c
slot: System board or motherboard
size: 13GiB
capabilities: ecc
configuration: errordetection=multi-bit-ecc
[3]
diff --git a/drivers/base/regmap/regmap-debugfs.c b/drivers/base/regmap/regmap-debugfs.c
index e5e1b3a01b1a..a6e144015406 100644
--- a/drivers/base/regmap/regmap-debugfs.c
+++ b/drivers/base/regmap/regmap-debugfs.c
+ printk("regmap_read_debugfs2\n");
buf = kmalloc(count, GFP_KERNEL);
if (!buf)
return -ENOMEM;
regmap_calc_tot_len(map, buf, count);
+ printk("regmap_read_debugfs3\n");
/* Work out which register we're starting at */
start_reg = regmap_debugfs_get_dump_start(map, from, *ppos, &p);
for (i = start_reg; i >= 0 && i <= to;
i = regmap_next_readable_reg(map, i)) {
+ printk("regmap_read_debugfs4 %d\n", i);
/* If we're in the region the user is trying to read */
if (p >= *ppos) {
/* ...but not beyond it */
if (buf_pos + map->debugfs_tot_len > count)
break;
+ printk("regmap_read_debugfs5 %llu\n", p);
/* Format the register */
snprintf(buf + buf_pos, count - buf_pos, "%.*x: ",
map->debugfs_reg_len, i - from);
buf_pos += map->debugfs_reg_len + 2;
/* Format the value, write all X if we can't read */
+ printk("regmap_read_debugfs6 map: %px, i: %d, val: %u\n", map, i, val);
ret = regmap_read(map, i, &val);
+ printk("regmap_read_debugfs6b\n");
if (ret == 0)
snprintf(buf + buf_pos, count - buf_pos,
"%.*x", map->debugfs_val_len, val);
[4]
[ 1150.122251] regmap_read_debugfs2
[ 1150.125547] regmap_read_debugfs3
[ 1150.128798] regmap_read_debugfs4 0
[ 1150.132291] regmap_read_debugfs5 0
[ 1150.135718] regmap_read_debugfs6 map: ffff80035ad63600, i: 0, val: 1461156912
[ 1150.142951] (NULL device *): map: ffff80035ad63600, map->dev: 0000000000000000, ret: 0, 0 => 7
[ 1150.151647] regmap_read_debugfs6b
[ 1150.161527] regmap_read_debugfs4 4
[ 1150.164947] regmap_read_debugfs5 14
[ 1150.168452] regmap_read_debugfs6 map: ffff80035ad63600, i: 4, val: 7
[ 1150.174886] (NULL device *): map: ffff80035ad63600, map->dev: 0000000000000000, ret: 0, 4 => 50001
[ 1150.183937] regmap_read_debugfs6b
[ 1150.193967] regmap_read_debugfs4 8
[ 1150.197383] regmap_read_debugfs5 28
[ 1150.200944] regmap_read_debugfs6 map: ffff80035ad63600, i: 8, val: 327681
[ 1150.207759] (NULL device *): map: ffff80035ad63600, map->dev: 0000000000000000, ret: 0, 8 => 85000f
[ 1150.216889] regmap_read_debugfs6b
[ 1150.226771] regmap_read_debugfs4 12
[ 1150.230336] regmap_read_debugfs5 42
[ 1150.233846] regmap_read_debugfs6 map: ffff80035ad63600, i: 12, val: 8716303
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