Re: [PATCH v9 09/12] lib/vsprintf: Make use of fwnode API to obtain node names and separators

From: Guenter Roeck
Date: Thu Jan 02 2020 - 17:54:27 EST

Hi,

On Thu, Oct 03, 2019 at 03:32:16PM +0300, Sakari Ailus wrote:
> Instead of implementing our own means of discovering parent nodes, node
> names or counting how many parents a node has, use the newly added
> functions in the fwnode API to obtain that information.
>
> Signed-off-by: Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxx>
> Reviewed-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
> Reviewed-by: Petr Mladek <pmladek@xxxxxxxx>
> ---

This patch results in a lockdep splat when running one of my qemu
emulations. See below for log and bisect results. A complete log
is available at
https://kerneltests.org/builders/qemu-arm-master/builds/1408/steps/qemubuildcommand/logs/stdio

Guenter

---
======================================================
WARNING: possible circular locking dependency detected
5.5.0-rc4-00066-g738d2902773e #1 Not tainted
------------------------------------------------------
swapper/0/1 is trying to acquire lock:
c1313b00 (logbuf_lock){-.-.}, at: vprintk_emit+0x68/0x2d4

but task is already holding lock:
ef030b90 (&(&n->list_lock)->rlock){..-.}, at: free_debug_processing+0x38/0x418

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (&(&n->list_lock)->rlock){..-.}:
___slab_alloc.constprop.23+0x12c/0x798
__slab_alloc.constprop.22+0x44/0x70
__kmalloc+0x384/0x41c
of_populate_phandle_cache+0xcc/0x148
of_core_init+0x8/0xbc
driver_init+0x1c/0x2c
kernel_init_freeable+0xac/0x1b4
kernel_init+0x8/0x118
ret_from_fork+0x14/0x20
0x0

-> #1 (devtree_lock){....}:
of_get_parent+0x18/0x34
of_fwnode_get_parent+0x34/0x40
fwnode_count_parents+0x28/0x58
fwnode_full_name_string+0x18/0xa0
device_node_string+0x490/0x4f0
pointer+0x440/0x4d8
vsnprintf+0x1bc/0x3d8
vscnprintf+0xc/0x24
vprintk_store+0x34/0x204
vprintk_emit+0x94/0x2d4
vprintk_default+0x20/0x28
printk+0x30/0x54
exynos4_pm_init_power_domain+0x220/0x258
do_one_initcall+0x8c/0x440
kernel_init_freeable+0x150/0x1b4
kernel_init+0x8/0x118
ret_from_fork+0x14/0x20
0x0

-> #0 (logbuf_lock){-.-.}:
lock_acquire+0xec/0x290
_raw_spin_lock+0x38/0x48
vprintk_emit+0x68/0x2d4
vprintk_default+0x20/0x28
printk+0x30/0x54
unwind_frame+0x6a8/0x6fc
walk_stackframe+0x2c/0x38
__save_stack_trace+0x84/0x8c
stack_trace_save+0x3c/0x5c
set_track+0x40/0x9c
free_debug_processing+0x1a4/0x418
__slab_free+0x2d4/0x510
kmem_cache_free+0x44c/0x49c
rcu_core+0x348/0x994
__do_softirq+0x164/0x668
irq_exit+0x16c/0x170
__handle_domain_irq+0x80/0xec
gic_handle_irq+0x58/0x9c
__irq_svc+0x70/0xb0
raid6_neon8_gen_syndrome_real+0x264/0x39c
raid6_neon8_gen_syndrome_real+0x264/0x39c

other info that might help us debug this:

Chain exists of:
logbuf_lock --> devtree_lock --> &(&n->list_lock)->rlock

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(&(&n->list_lock)->rlock);
lock(devtree_lock);
lock(&(&n->list_lock)->rlock);
lock(logbuf_lock);

*** DEADLOCK ***

2 locks held by swapper/0/1:
#0: c131466c (rcu_callback){....}, at: rcu_core+0x304/0x994
#1: ef030b90 (&(&n->list_lock)->rlock){..-.}, at: free_debug_processing+0x38/0x418

stack backtrace:
CPU: 1 PID: 1 Comm: swapper/0 Not tainted 5.5.0-rc4-00066-g738d2902773e #1
Hardware name: SAMSUNG EXYNOS (Flattened Device Tree)
[<c0113264>] (unwind_backtrace) from [<c010e448>] (show_stack+0x10/0x14)
[<c010e448>] (show_stack) from [<c0c9b754>] (dump_stack+0xa4/0xd0)
[<c0c9b754>] (dump_stack) from [<c018cbd8>] (check_noncircular+0x258/0x274)
[<c018cbd8>] (check_noncircular) from [<c019043c>] (__lock_acquire+0x1870/0x2860)
[<c019043c>] (__lock_acquire) from [<c018e088>] (lock_acquire+0xec/0x290)
[<c018e088>] (lock_acquire) from [<c0cbf278>] (_raw_spin_lock+0x38/0x48)
[<c0cbf278>] (_raw_spin_lock) from [<c01a1f84>] (vprintk_emit+0x68/0x2d4)
[<c01a1f84>] (vprintk_emit) from [<c01a2210>] (vprintk_default+0x20/0x28)
[<c01a2210>] (vprintk_default) from [<c01a2844>] (printk+0x30/0x54)
[<c01a2844>] (printk) from [<c0113210>] (unwind_frame+0x6a8/0x6fc)
[<c0113210>] (unwind_frame) from [<c010ddf0>] (walk_stackframe+0x2c/0x38)
[<c010ddf0>] (walk_stackframe) from [<c010df54>] (__save_stack_trace+0x84/0x8c)
[<c010df54>] (__save_stack_trace) from [<c01c2d40>] (stack_trace_save+0x3c/0x5c)
[<c01c2d40>] (stack_trace_save) from [<c02ae258>] (set_track+0x40/0x9c)
[<c02ae258>] (set_track) from [<c02b06a8>] (free_debug_processing+0x1a4/0x418)
[<c02b06a8>] (free_debug_processing) from [<c02b0bf0>] (__slab_free+0x2d4/0x510)
[<c02b0bf0>] (__slab_free) from [<c02b17ac>] (kmem_cache_free+0x44c/0x49c)
[<c02b17ac>] (kmem_cache_free) from [<c01bd608>] (rcu_core+0x348/0x994)
[<c01bd608>] (rcu_core) from [<c010230c>] (__do_softirq+0x164/0x668)
[<c010230c>] (__do_softirq) from [<c0131310>] (irq_exit+0x16c/0x170)
[<c0131310>] (irq_exit) from [<c01a3740>] (__handle_domain_irq+0x80/0xec)
[<c01a3740>] (__handle_domain_irq) from [<c0630828>] (gic_handle_irq+0x58/0x9c)
[<c0630828>] (gic_handle_irq) from [<c0101a70>] (__irq_svc+0x70/0xb0)
Exception stack(0xef19bd30 to 0xef19bd78)
bd20: c0d43e50 c0d43e60 ef19bebc c0d43e70
bd40: c0d43e20 c0d43e10 00000400 00000430 00000440 00000450 00000460 00000470
bd60: c0d43e40 ef19bd80 c0d43e30 c0625c00 20000013 ffffffff
[<c0101a70>] (__irq_svc) from [<c0625c00>] (raid6_neon8_gen_syndrome_real+0x264/0x39c)

---
Bisect:

# bad: [738d2902773e30939a982c8df7a7f94293659810] Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net
# good: [219d54332a09e8d8741c1e1982f5eae56099de85] Linux 5.4
git bisect start 'HEAD' 'v5.4'
# bad: [8c39f71ee2019e77ee14f88b1321b2348db51820] Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net
git bisect bad 8c39f71ee2019e77ee14f88b1321b2348db51820
# good: [3b397c7ccafe0624018cb09fc96729f8f6165573] Merge tag 'regmap-v5.5' of git://git.kernel.org/pub/scm/linux/kernel/git/broonie/regmap
git bisect good 3b397c7ccafe0624018cb09fc96729f8f6165573
# bad: [89d57dddd7d319ded00415790a0bb3c954b7e386] Merge tag 'media/v5.5-1' of git://git.kernel.org/pub/scm/linux/kernel/git/mchehab/linux-media
git bisect bad 89d57dddd7d319ded00415790a0bb3c954b7e386
# good: [9e7a03233e02afd3ee061e373355f34d7254f1e6] Merge tag 'pm-5.5-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm
git bisect good 9e7a03233e02afd3ee061e373355f34d7254f1e6
# good: [09578eacaaa44149738267083ccc050990409f86] Merge tag 'asoc-v5.5-2' of https://git.kernel.org/pub/scm/linux/kernel/git/broonie/sound into for-linus
git bisect good 09578eacaaa44149738267083ccc050990409f86
# good: [1c7ae4a51298d52a21f63b2214657982036c7498] media: ad5820: Add support for of-autoload
git bisect good 1c7ae4a51298d52a21f63b2214657982036c7498
# good: [99cf8a7074c4ce3ff3685cd389f54e7bd4bbf510] media: dt-bindings: Fix building error for dt_binding_check
git bisect good 99cf8a7074c4ce3ff3685cd389f54e7bd4bbf510
# good: [782b59711e1561ee0da06bc478ca5e8249aa8d09] Merge branch 'acpi-mm'
git bisect good 782b59711e1561ee0da06bc478ca5e8249aa8d09
# good: [0ca40f41d795fd91811e44506bb73d0b9ca33bdd] Merge branch 'patchwork' into v4l_for_linus
git bisect good 0ca40f41d795fd91811e44506bb73d0b9ca33bdd
# bad: [a00351687f8a05773c1c57be80a5bbca68fa9ae8] software node: remove DEV_PROP_MAX
git bisect bad a00351687f8a05773c1c57be80a5bbca68fa9ae8
# good: [9af7706492f985867d070861fe39fee0fe41326f] lib/vsprintf: Remove support for %pF and %pf in favour of %pS and %ps
git bisect good 9af7706492f985867d070861fe39fee0fe41326f
# bad: [83abc5a77f3b028b8c845c39ce4053119e1de35b] lib/vsprintf: OF nodes are first and foremost, struct device_nodes
git bisect bad 83abc5a77f3b028b8c845c39ce4053119e1de35b
# bad: [a92eb7621b9fb2c28a588ce333d226f56fab6a85] lib/vsprintf: Make use of fwnode API to obtain node names and separators
git bisect bad a92eb7621b9fb2c28a588ce333d226f56fab6a85
# good: [1586c5ae2f9310235b5e70abe712c73fc32eb98f] lib/vsprintf: Add a note on re-using %pf or %pF
git bisect good 1586c5ae2f9310235b5e70abe712c73fc32eb98f
# first bad commit: [a92eb7621b9fb2c28a588ce333d226f56fab6a85] lib/vsprintf: Make use of fwnode API to obtain node names and separators