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Date:   Thu, 21 Jan 2021 17:07:04 -0800
From:   Saravana Kannan <saravanak@...gle.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Marc Zyngier <maz@...nel.org>,
        Android Kernel Team <kernel-team@...roid.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [TEST PATCH v1] driver: core: Make fw_devlink=on more forgiving

On Thu, Jan 21, 2021 at 2:38 AM Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
>
> Hi Saravana,
>
> On Thu, Jan 21, 2021 at 9:28 AM Saravana Kannan <saravanak@...gle.com> wrote:
> > On Thu, Jan 21, 2021 at 12:22 AM Saravana Kannan <saravanak@...gle.com> wrote:
> > > This patch is for test purposes only and pretty experimental. Code might
> > > not be optimized, clean, formatted properly, etc.
> > >
> > > Please review it only for functional bugs like locking bugs, wrong
> > > logic, etc.
> > >
> > > It's basically trying to figure out which devices will never probe and
> > > ignore them. Might not always work.
> > >
> > > Marek, Geert, Marc,
> > >
> > > Can you please try this patch INSTEAD of the other workarounds we found?
>
> Thanks for your patch!
>
> > Oh and can you please also try with the CONFIG_MODULES enabled vs
> > disabled? Or have it disabled but fix the patch so the condition
> > always evaluates to true.
>
> With CONFIG_MODULES=y, it fails in the same way as before (no "Deleting
> {fwnode,dev} link" messages seen), with a new lockdep warning:
>
> +======================================================
> +WARNING: possible circular locking dependency detected
> +5.11.0-rc2-salvator-x-00009-gdf1dd3208a90 #941 Not tainted
> +------------------------------------------------------
> +swapper/0/1 is trying to acquire lock:
> +ffffffc0110da488 (fwnode_link_lock){+.+.}-{4:4}, at: fw_devlink_unblock_probe+0
> x50/0x158
> +
> +but task is already holding lock:
> +ffffffc0110da988 (deferred_probe_mutex){+.+.}-{4:4}, at: deferred_probe_initcal
> l+0xe4/0x12c
> +
> +which lock already depends on the new lock.
> +
> +
> +the existing dependency chain (in reverse order) is:
> +
> +-> #2 (deferred_probe_mutex){+.+.}-{4:4}:
> +       lock_acquire+0x344/0x390
> +       __mutex_lock+0xc0/0x37c
> +       mutex_lock_nested+0x34/0x48
> +       driver_deferred_probe_add+0x2c/0x88
> +       device_links_driver_bound+0x11c/0x1ac
> +       driver_bound+0x64/0xac
> +       really_probe+0x304/0x338
> +       driver_probe_device+0x98/0xa8
> +       device_driver_attach+0x40/0x68
> +       __driver_attach+0xa8/0xac
> +       bus_for_each_dev+0x6c/0xb8
> +       driver_attach+0x20/0x28
> +       bus_add_driver+0x16c/0x1b0
> +       driver_register+0xac/0xe4
> +       __platform_driver_probe+0x88/0xe0
> +       cpg_mssr_init+0x20/0x28
> +       do_one_initcall+0xf0/0x280
> +       kernel_init_freeable+0x1e0/0x1e4
> +       kernel_init+0x10/0x108
> +       ret_from_fork+0x10/0x18
> +
> +-> #1 (device_links_lock){+.+.}-{4:4}:
> +       lock_acquire+0x344/0x390
> +       __mutex_lock+0xc0/0x37c
> +       mutex_lock_nested+0x34/0x48
> +       device_links_write_lock+0x18/0x20
> +       device_link_add+0xfc/0x3e4
> +       fw_devlink_create_devlink+0x40/0xec
> +       device_add+0x640/0x6ac
> +       of_device_add+0x38/0x40
> +       of_platform_device_create_pdata+0xb0/0xcc
> +       of_platform_bus_create+0x2b8/0x364
> +       of_platform_bus_create+0x300/0x364
> +       of_platform_populate+0x7c/0xd8
> +       of_platform_default_populate+0x20/0x28
> +       of_platform_default_populate_init+0x80/0xb8
> +       do_one_initcall+0xf0/0x280
> +       kernel_init_freeable+0x1e0/0x1e4
> +       kernel_init+0x10/0x108
> +       ret_from_fork+0x10/0x18
> +
> +-> #0 (fwnode_link_lock){+.+.}-{4:4}:
> +       check_noncircular+0x74/0xa4
> +       __lock_acquire+0xdd0/0x10a8
> +       lock_acquire+0x344/0x390
> +       __mutex_lock+0xc0/0x37c
> +       mutex_lock_nested+0x34/0x48
> +       fw_devlink_unblock_probe+0x50/0x158
> +       deferred_probe_initcall+0x11c/0x12c
> +       do_one_initcall+0xf0/0x280
> +       kernel_init_freeable+0x1e0/0x1e4
> +       kernel_init+0x10/0x108
> +       ret_from_fork+0x10/0x18
> +
> +other info that might help us debug this:
> +
> +Chain exists of:
> +  fwnode_link_lock --> device_links_lock --> deferred_probe_mutex
> +
> + Possible unsafe locking scenario:
> +
> +       CPU0                    CPU1
> +       ----                    ----
> +  lock(deferred_probe_mutex);
> +                               lock(device_links_lock);
> +                               lock(deferred_probe_mutex);
> +  lock(fwnode_link_lock);
> +
> + *** DEADLOCK ***
> +
> +1 lock held by swapper/0/1:
> + #0: ffffffc0110da988 (deferred_probe_mutex){+.+.}-{4:4}, at:
> deferred_probe_initcall+0xe4/0x12c
> +
> +stack backtrace:
> +CPU: 2 PID: 1 Comm: swapper/0 Not tainted
> 5.11.0-rc2-salvator-x-00009-gdf1dd3208a90 #941
> +Hardware name: Renesas Salvator-X 2nd version board based on r8a77951 (DT)
> +Call trace:
> + dump_backtrace+0x0/0x188
> + show_stack+0x14/0x28
> + dump_stack+0xf0/0x140
> + print_circular_bug.isra.0+0x1b0/0x1e8
> + check_noncircular+0x74/0xa4
> + __lock_acquire+0xdd0/0x10a8
> + lock_acquire+0x344/0x390
> + __mutex_lock+0xc0/0x37c
> + mutex_lock_nested+0x34/0x48
> + fw_devlink_unblock_probe+0x50/0x158
> + deferred_probe_initcall+0x11c/0x12c
> + do_one_initcall+0xf0/0x280
> + kernel_init_freeable+0x1e0/0x1e4
> + kernel_init+0x10/0x108
> + ret_from_fork+0x10/0x18
>
> With CONFIG_MODULES disabled, it deletes one link, and hangs:
>
> +platform e61c0000.interrupt-controller: Deleting dev link to
> e6180000.system-controller
> +INFO: task swapper/0:1 blocked for more than 120 seconds.
> +      Not tainted 5.11.0-rc2-salvator-x-00009-gdf1dd3208a90-dirty #944
> +"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> +task:swapper/0       state:D stack:    0 pid:    1 ppid:     0 flags:0x00000008
> +Call trace:
> + __switch_to+0xa8/0x10c
> + __schedule+0x54c/0x728
> + schedule+0x7c/0xc0
> + schedule_preempt_disabled+0x10/0x1c
> + __mutex_lock+0x1e8/0x37c
> + mutex_lock_nested+0x34/0x48
> + driver_deferred_probe_del+0x28/0x8c
> + device_del+0x198/0x30c
> + device_unregister+0x14/0x28
> + __device_link_del+0x4c/0x5c
> + device_link_drop_managed+0x44/0x50
> + fw_devlink_unblock_probe+0x1e8/0x230
> + deferred_probe_initcall+0x11c/0x12c
> + do_one_initcall+0xf0/0x240
> + kernel_init_freeable+0x1e0/0x1e4
> + kernel_init+0x10/0x108
> + ret_from_fork+0x10/0x18
> +INFO: lockdep is turned off.
>
> Gr{oetje,eeting}s,
>
>                         Geert

Thanks for the tests Marek and Geert! I'll probably scrap this and redo it.

-Saravana

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