Re: [TEST PATCH v1] driver: core: Make fw_devlink=on more forgiving

[Geert Uytterhoeven <geert@linux-m68k.org>]

Hi Saravana,

On Thu, Jan 21, 2021 at 9:28 AM Saravana Kannan <saravanak@google.com> wrote:
> On Thu, Jan 21, 2021 at 12:22 AM Saravana Kannan <saravanak@google.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


--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds