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