Date:   Wed, 15 Jul 2020 15:13:56 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Saravana Kannan <saravanak@...gle.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        linux-kernel@...r.kernel.org, John Stultz <john.stultz@...aro.org>,
        kernel-team@...roid.com
Subject: Re: [PATCH v3 1/3] driver core: Expose device link details in sysfs

Hi,

On Thu, May 21, 2020 at 12:17:58PM -0700, Saravana Kannan wrote:
> It's helpful to be able to look at device link details from sysfs. So,
> expose it in sysfs.
> 
> Say device-A is supplier of device-B. These are the additional files
> this patch would create:
> 
> /sys/class/devlink/device-A:device-B/
> 	auto_remove_on
> 	consumer/ -> .../device-B/
> 	runtime_pm
> 	status
> 	supplier/ -> .../device-A/
> 	sync_state_only
> 
> /sys/devices/.../device-A/
> 	consumer:device-B/ -> /sys/class/devlink/device-A:device-B/
> 
> /sys/devices/.../device-B/
> 	supplier:device-A/ -> /sys/class/devlink/device-A:device-B/
> 
> That way:
> To get a list of all the device link in the system:
> ls /sys/class/devlink/
> 
> To get the consumer names and links of a device:
> ls -d /sys/devices/.../device-X/consumer:*
> 
> To get the supplier names and links of a device:
> ls -d /sys/devices/.../device-X/supplier:*
> 
> Signed-off-by: Saravana Kannan <saravanak@...gle.com>

This patch creates a lot of noise in linux-next when booting various
qemu images. Example log output as well as bisect results below.
Reverting the patch fixes the problem.

Guenter

---
BUG: sleeping function called from invalid context at kernel/locking/mutex.c:935
in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 13, name: kworker/0:1
2 locks held by kworker/0:1/13:
 #0: c78048a4 ((wq_completion)rcu_gp){+.+.}-{0:0}, at: process_one_work+0x1a0/0x728
 #1: c78ebf18 ((work_completion)(&sdp->work)){+.+.}-{0:0}, at: process_one_work+0x1a0/0x728
Preemption disabled at:
[<c0085bb4>] srcu_invoke_callbacks+0xc0/0x158
CPU: 0 PID: 13 Comm: kworker/0:1 Not tainted 5.8.0-rc5-next-20200715 #1
Hardware name: Freescale i.MX25 (Device Tree Support)
Workqueue: rcu_gp srcu_invoke_callbacks
[<c0010fe4>] (unwind_backtrace) from [<c000e740>] (show_stack+0x10/0x18)
[<c000e740>] (show_stack) from [<c050985c>] (dump_stack+0x20/0x2c)
[<c050985c>] (dump_stack) from [<c00496e4>] (___might_sleep+0x1d0/0x2cc)
[<c00496e4>] (___might_sleep) from [<c09105e8>] (__mutex_lock+0x38/0x654)
[<c09105e8>] (__mutex_lock) from [<c0910c20>] (mutex_lock_nested+0x1c/0x28)
[<c0910c20>] (mutex_lock_nested) from [<c05b25dc>] (device_del+0x2c/0x3f0)
[<c05b25dc>] (device_del) from [<c05b2a10>] (__device_link_free_srcu+0x50/0x64)
[<c05b2a10>] (__device_link_free_srcu) from [<c0085bc4>] (srcu_invoke_callbacks+0xd0/0x158)
[<c0085bc4>] (srcu_invoke_callbacks) from [<c003ad2c>] (process_one_work+0x284/0x728)
[<c003ad2c>] (process_one_work) from [<c003b1fc>] (worker_thread+0x2c/0x52c)
[<c003b1fc>] (worker_thread) from [<c0042df8>] (kthread+0x154/0x180)
[<c0042df8>] (kthread) from [<c0008530>] (ret_from_fork+0x14/0x24)
Exception stack(0xc78ebfb0 to 0xc78ebff8)
bfa0:                                     00000000 00000000 00000000 00000000
bfc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
bfe0: 00000000 00000000 00000000 00000000 00000013 00000000
BUG: scheduling while atomic: kworker/0:1/13/0x00000201
3 locks held by kworker/0:1/13:
 #0: c78048a4 ((wq_completion)rcu_gp){+.+.}-{0:0}, at: process_one_work+0x1a0/0x728
 #1: c78ebf18 ((work_completion)(&sdp->work)){+.+.}-{0:0}, at: process_one_work+0x1a0/0x728
 #2: c0cf5710 (gdp_mutex){+.+.}-{3:3}, at: cleanup_glue_dir.part.14+0x14/0xa0
Modules linked in:
Preemption disabled at:
[<c0085bb4>] srcu_invoke_callbacks+0xc0/0x158
CPU: 0 PID: 13 Comm: kworker/0:1 Tainted: G        W         5.8.0-rc5-next-20200715 #1
Hardware name: Freescale i.MX25 (Device Tree Support)
Workqueue: rcu_gp srcu_invoke_callbacks
[<c0010fe4>] (unwind_backtrace) from [<c000e740>] (show_stack+0x10/0x18)
[<c000e740>] (show_stack) from [<c050985c>] (dump_stack+0x20/0x2c)
[<c050985c>] (dump_stack) from [<c0049910>] (__schedule_bug+0x88/0xf0)
[<c0049910>] (__schedule_bug) from [<c090e148>] (__schedule+0x5f0/0x824)
[<c090e148>] (__schedule) from [<c090e3d0>] (schedule+0x54/0x128)
[<c090e3d0>] (schedule) from [<c090e838>] (schedule_preempt_disabled+0x14/0x28)
[<c090e838>] (schedule_preempt_disabled) from [<c0910744>] (__mutex_lock+0x194/0x654)
[<c0910744>] (__mutex_lock) from [<c0910c20>] (mutex_lock_nested+0x1c/0x28)
[<c0910c20>] (mutex_lock_nested) from [<c05b1d5c>] (cleanup_glue_dir.part.14+0x14/0xa0)
[<c05b1d5c>] (cleanup_glue_dir.part.14) from [<c05b296c>] (device_del+0x3bc/0x3f0)
[<c05b296c>] (device_del) from [<c05b2a10>] (__device_link_free_srcu+0x50/0x64)
[<c05b2a10>] (__device_link_free_srcu) from [<c0085bc4>] (srcu_invoke_callbacks+0xd0/0x158)
[<c0085bc4>] (srcu_invoke_callbacks) from [<c003ad2c>] (process_one_work+0x284/0x728)
[<c003ad2c>] (process_one_work) from [<c003b1fc>] (worker_thread+0x2c/0x52c)
[<c003b1fc>] (worker_thread) from [<c0042df8>] (kthread+0x154/0x180)
[<c0042df8>] (kthread) from [<c0008530>] (ret_from_fork+0x14/0x24)
Exception stack(0xc78ebfb0 to 0xc78ebff8)
bfa0:                                     00000000 00000000 00000000 00000000
bfc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
bfe0: 00000000 00000000 00000000 00000000 00000013 00000000
------------[ cut here ]------------

---
# bad: [ca0e494af5edb59002665bf12871e94b4163a257] Add linux-next specific files for 20200715
# good: [11ba468877bb23f28956a35e896356252d63c983] Linux 5.8-rc5
git bisect start 'HEAD' 'v5.8-rc5'
# good: [8a21074e4724ce86b4e1a8fdc271081a86303014] Merge remote-tracking branch 'crypto/master'
git bisect good 8a21074e4724ce86b4e1a8fdc271081a86303014
# good: [71f459b5cd96681f615e5c920b3a38ab89e8b5f1] Merge remote-tracking branch 'audit/next'
git bisect good 71f459b5cd96681f615e5c920b3a38ab89e8b5f1
# bad: [5a310f73f874211ee7aa570b308d50def85aff1c] Merge remote-tracking branch 'thunderbolt/next'
git bisect bad 5a310f73f874211ee7aa570b308d50def85aff1c
# good: [db01f1b1e840f46bdd64c6c846e7b3246bdff55a] Merge remote-tracking branch 'kvm/linux-next'
git bisect good db01f1b1e840f46bdd64c6c846e7b3246bdff55a
# bad: [89947fbc4b34bfdef7ade2b26274e78b32d4e39f] Merge remote-tracking branch 'usb/usb-next'
git bisect bad 89947fbc4b34bfdef7ade2b26274e78b32d4e39f
# bad: [c845fc08689b52c05c0201614ac89f7978caa169] Merge remote-tracking branch 'driver-core/driver-core-next'
git bisect bad c845fc08689b52c05c0201614ac89f7978caa169
# good: [4621ddca720ceb9b45725acd428e0389e3c0b59b] Merge remote-tracking branch 'drivers-x86/for-next'
git bisect good 4621ddca720ceb9b45725acd428e0389e3c0b59b
# good: [fac3dee864e971dff81dd4969c361b2b373109c0] Merge remote-tracking branch 'leds/for-next'
git bisect good fac3dee864e971dff81dd4969c361b2b373109c0
# good: [55c7549819e438f40a3ef1d8ac5c38b73390bcb7] scripts: add dummy report mode to add_namespace.cocci
git bisect good 55c7549819e438f40a3ef1d8ac5c38b73390bcb7
# good: [fe940d7362e6d7a5e5086581d0462e00ba766992] driver core: Drop mention of obsolete bus rwsem from kernel-doc
git bisect good fe940d7362e6d7a5e5086581d0462e00ba766992
# bad: [da6d647598a6d182eb6a0344a7b14ae005244399] driver core: Add waiting_for_supplier sysfs file for devices
git bisect bad da6d647598a6d182eb6a0344a7b14ae005244399
# bad: [8fd456ec0cf03875908d6b67c1cd20cf0a7b4474] driver core: Add state_synced sysfs file for devices that support it
git bisect bad 8fd456ec0cf03875908d6b67c1cd20cf0a7b4474
# bad: [287905e68dd29873bcb7986a8290cd1e4cfde600] driver core: Expose device link details in sysfs
git bisect bad 287905e68dd29873bcb7986a8290cd1e4cfde600
# first bad commit: [287905e68dd29873bcb7986a8290cd1e4cfde600] driver core: Expose device link details in sysfs

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