Adding many more people and lkml to the cc list. Please don't poke people in private, but always cc a relevant mailing list.
On Sat, Feb 8, 2014 at 6:24 AM, Jane Li <[email protected]> wrote: > Hi Danial Vetter, > > I found you had added console_lock_dep_map in commit daee7797 (console: > implement lockdep support for console_lock). I encounter another circular > lock warning related to it. > > Sequence: > > enter suspend -> resume -> plug-out CPUx (echo 0 > cpux/online) > > Then, lockdep will show warning as following: > > ====================================================== > [ INFO: possible circular locking dependency detected ] > 3.10.0 #2 Tainted: G O > ------------------------------------------------------- > sh/1271 is trying to acquire lock: > (console_lock){+.+.+.}, at: [<c06ebf7c>] console_cpu_notify+0x20/0x2c > but task is already holding lock: > (cpu_hotplug.lock){+.+.+.}, at: [<c012b4e8>] cpu_hotplug_begin+0x2c/0x58 > which lock already depends on the new lock. > > the existing dependency chain (in reverse order) is: > -> #2 (cpu_hotplug.lock){+.+.+.}: > [<c017bb7c>] lock_acquire+0x98/0x12c > [<c06f5014>] mutex_lock_nested+0x50/0x3d8 > [<c012b4e8>] cpu_hotplug_begin+0x2c/0x58 > [<c06ebfac>] _cpu_up+0x24/0x154 > [<c06ec140>] cpu_up+0x64/0x84 > [<c0981834>] smp_init+0x9c/0xd4 > [<c0973880>] kernel_init_freeable+0x78/0x1c8 > [<c06e7f40>] kernel_init+0x8/0xe4 > [<c010eec8>] ret_from_fork+0x14/0x2c > > -> #1 (cpu_add_remove_lock){+.+.+.}: > [<c017bb7c>] lock_acquire+0x98/0x12c > [<c06f5014>] mutex_lock_nested+0x50/0x3d8 > [<c012b758>] disable_nonboot_cpus+0x8/0xe8 > [<c016b83c>] suspend_devices_and_enter+0x214/0x448 > [<c016bc54>] pm_suspend+0x1e4/0x284 > [<c016bdcc>] try_to_suspend+0xa4/0xbc > [<c0143848>] process_one_work+0x1c4/0x4fc > [<c0143f80>] worker_thread+0x138/0x37c > [<c014aaf8>] kthread+0xa4/0xb0 > [<c010eec8>] ret_from_fork+0x14/0x2c > > -> #0 (console_lock){+.+.+.}: > [<c017b5d0>] __lock_acquire+0x1b38/0x1b80 > [<c017bb7c>] lock_acquire+0x98/0x12c > [<c01288c4>] console_lock+0x54/0x68 > [<c06ebf7c>] console_cpu_notify+0x20/0x2c > [<c01501d4>] notifier_call_chain+0x44/0x84 > [<c012b448>] __cpu_notify+0x2c/0x48 > [<c012b5b0>] cpu_notify_nofail+0x8/0x14 > [<c06e81bc>] _cpu_down+0xf4/0x258 > [<c06e8344>] cpu_down+0x24/0x40 > [<c06e921c>] store_online+0x30/0x74 > [<c03b7298>] dev_attr_store+0x18/0x24 > [<c025fc5c>] sysfs_write_file+0x16c/0x19c > [<c0207a98>] vfs_write+0xb4/0x190 > [<c0207e58>] SyS_write+0x3c/0x70 > [<c010ee00>] ret_fastChain exists of: > console_lock --> cpu_add_remove_lock --> cpu_hotplug.lock > > Possible unsafe locking scenario: > CPU0 CPU1 > ---- ---- > lock(cpu_hotplug.lock); > lock(cpu_add_remove_lock); > lock(cpu_hotplug.lock); > lock(console_lock); > *** DEADLOCK *** > > > > Analyze this information, there are three locks involved in two sequence: > > pm suspend: console_lock (@suspend_console()) -> cpu_add_remove_lock > (@disable_nonboot_cpus()) -> cpu_hotplug.lock (@_cpu_down()) > > Plug-out CPUx: cpu_add_remove_lock (@(cpu_down()) -> > cpu_hotplug.lock (@_cpu_down()) -> console_lock (@console_cpu_notify()) => > Lockdeps prints warning log. > > > I check code and there should be not real deadlock, as flag of > console_suspended can protect this. > > Do you know how to avoid this warning? I think the right approach here is to add a new function to do the console flushing: /** * console_flush - flush dmesg if console isn't suspended * * console_unlock always flushes the dmesg buffer, so just try to * grab&drop the console lock. If that fails we know that the current * holder will eventually drop the console lock and so flush the dmesg * buffers at the earliest possible time. */ void console_flush(void) { if (console_trylock()) console_unlock(); } Then use that instead of the unconditional console_lock/unlock pair int the console_cpu_notitifier. Since that's practically the patch already feel free to smash a Signed-off-by: Daniel Vetter <[email protected]> on top if it works. Cheers, Daniel -- Daniel Vetter Software Engineer, Intel Corporation +41 (0) 79 365 57 48 - http://blog.ffwll.ch -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
