Re: [PATCH] i2c_powermac: shut up lockdep warning
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Date: 2016-09-26 21:03:59
On Mon, 2016-09-26 at 14:00 +0300, Denis Kirjanov wrote:
On Wednesday, September 21, 2016, Denis Kirjanov <kda@linux-powerpc.o rg> wrote:quoted
That's unclear why lockdep shows the following warning but adding a lockdep class to struct pmac_i2c_bus solves itHI Ben, could you give any comments on this?
I haven't quite figured out real reason for lockdep complaint, the output is as usual terribly hard to parse, but adding a lock class doesn't sound like something wrong to do so ... Ben.
Thanks!quoted
[ 20.507795] ====================================================== [ 20.507796] [ INFO: possible circular locking dependency detected ] [ 20.507800] 4.8.0-rc7-00037-gd2ffb01 #21 Not tainted [ 20.507801] ---------------------------------------------------- --- [ 20.507803] swapper/0/1 is trying to acquire lock: [ 20.507818] (&bus->mutex){+.+.+.}, at: [<c000000000052830>] .pmac_i2c_open+0x30/0x100 [ 20.507819] [ 20.507819] but task is already holding lock: [ 20.507829] (&policy->rwsem){+.+.+.}, at: [<c00000000068adcc>] .cpufreq_online+0x1ac/0x9d0 [ 20.507830] [ 20.507830] which lock already depends on the new lock. [ 20.507830] [ 20.507832] [ 20.507832] the existing dependency chain (in reverse order) is: [ 20.507837] [ 20.507837] -> #4 (&policy->rwsem){+.+.+.}: [ 20.507844] [<c00000000082385c>] .down_write+0x6c/0x110 [ 20.507849] [<c00000000068adcc>] .cpufreq_online+0x1ac/0x9d0 [ 20.507855] [<c0000000004d76d8>] .subsys_interface_register+0xb8/0x110 [ 20.507860] [<c000000000689bb0>] .cpufreq_register_driver+0x1d0/0x250 [ 20.507866] [<c000000000b4f8f4>] .g5_cpufreq_init+0x9cc/0xa28 [ 20.507872] [<c00000000000a98c>] .do_one_initcall+0x5c/0x1d0 [ 20.507878] [<c000000000b0f86c>] .kernel_init_freeable+0x1ac/0x28c [ 20.507883] [<c00000000000b3bc>] .kernel_init+0x1c/0x140 [ 20.507887] [<c0000000000098f4>] .ret_from_kernel_thread+0x58/0x64 [ 20.507894] [ 20.507894] -> #3 (subsys mutex#2){+.+.+.}: [ 20.507899] [<c000000000820448>] .mutex_lock_nested+0xa8/0x590 [ 20.507903] [<c0000000004d7f24>] .bus_probe_device+0x44/0xe0 [ 20.507907] [<c0000000004d5208>] .device_add+0x508/0x730 [ 20.507911] [<c0000000004dd528>] .register_cpu+0x118/0x190 [ 20.507916] [<c000000000b14450>] .topology_init+0x148/0x248 [ 20.507921] [<c00000000000a98c>] .do_one_initcall+0x5c/0x1d0 [ 20.507925] [<c000000000b0f86c>] .kernel_init_freeable+0x1ac/0x28c [ 20.507929] [<c00000000000b3bc>] .kernel_init+0x1c/0x140 [ 20.507934] [<c0000000000098f4>] .ret_from_kernel_thread+0x58/0x64 [ 20.507939] [ 20.507939] -> #2 (cpu_add_remove_lock){+.+.+.}: [ 20.507944] [<c000000000820448>] .mutex_lock_nested+0xa8/0x590 [ 20.507950] [<c000000000087a9c>] .register_cpu_notifier+0x2c/0x70 [ 20.507955] [<c000000000b267e0>] .spawn_ksoftirqd+0x18/0x4c [ 20.507959] [<c00000000000a98c>] .do_one_initcall+0x5c/0x1d0 [ 20.507964] [<c000000000b0f770>] .kernel_init_freeable+0xb0/0x28c [ 20.507968] [<c00000000000b3bc>] .kernel_init+0x1c/0x140 [ 20.507972] [<c0000000000098f4>] .ret_from_kernel_thread+0x58/0x64 [ 20.507978] [ 20.507978] -> #1 (&host->mutex){+.+.+.}: [ 20.507982] [<c000000000820448>] .mutex_lock_nested+0xa8/0x590 [ 20.507987] [<c0000000000527e8>] .kw_i2c_open+0x18/0x30 [ 20.507991] [<c000000000052894>] .pmac_i2c_open+0x94/0x100 [ 20.507995] [<c000000000b220a0>] .smp_core99_probe+0x260/0x410 [ 20.507999] [<c000000000b185bc>] .smp_prepare_cpus+0x280/0x2ac [ 20.508003] [<c000000000b0f748>] .kernel_init_freeable+0x88/0x28c [ 20.508008] [<c00000000000b3bc>] .kernel_init+0x1c/0x140 [ 20.508012] [<c0000000000098f4>] .ret_from_kernel_thread+0x58/0x64 [ 20.508018] [ 20.508018] -> #0 (&bus->mutex){+.+.+.}: [ 20.508023] [<c0000000000ed5b4>] .lock_acquire+0x84/0x100 [ 20.508027] [<c000000000820448>] .mutex_lock_nested+0xa8/0x590 [ 20.508032] [<c000000000052830>] .pmac_i2c_open+0x30/0x100 [ 20.508037] [<c000000000052e14>] .pmac_i2c_do_begin+0x34/0x120 [ 20.508040] [<c000000000056bc0>] .pmf_call_one+0x50/0xd0 [ 20.508045] [<c00000000068ff1c>] .g5_pfunc_switch_volt+0x2c/0xc0 [ 20.508050] [<c00000000068fecc>] .g5_pfunc_switch_freq+0x1cc/0x1f0 [ 20.508054] [<c00000000068fc2c>] .g5_cpufreq_target+0x2c/0x40 [ 20.508058] [<c0000000006873ec>] .__cpufreq_driver_target+0x23c/0x840 [ 20.508062] [<c00000000068c798>] .cpufreq_gov_performance_limits+0x18/0x30 [ 20.508067] [<c00000000068915c>] .cpufreq_start_governor+0xac/0x100 [ 20.508071] [<c00000000068a788>] .cpufreq_set_policy+0x208/0x260 [ 20.508076] [<c00000000068abdc>] .cpufreq_init_policy+0x6c/0xb0 [ 20.508081] [<c00000000068ae70>] .cpufreq_online+0x250/0x9d0 [ 20.508085] [<c0000000004d76d8>] .subsys_interface_register+0xb8/0x110 [ 20.508090] [<c000000000689bb0>] .cpufreq_register_driver+0x1d0/0x250 [ 20.508094] [<c000000000b4f8f4>] .g5_cpufreq_init+0x9cc/0xa28 [ 20.508099] [<c00000000000a98c>] .do_one_initcall+0x5c/0x1d0 [ 20.508103] [<c000000000b0f86c>] .kernel_init_freeable+0x1ac/0x28c [ 20.508107] [<c00000000000b3bc>] .kernel_init+0x1c/0x140 [ 20.508112] [<c0000000000098f4>] .ret_from_kernel_thread+0x58/0x64 [ 20.508113] [ 20.508113] other info that might help us debug this: [ 20.508113] [ 20.508121] Chain exists of: [ 20.508121] &bus->mutex --> subsys mutex#2 --> &policy->rwsem [ 20.508121] [ 20.508123] Possible unsafe locking scenario: [ 20.508123] [ 20.508124] CPU0 CPU1 [ 20.508125] ---- ---- [ 20.508128] lock(&policy->rwsem); [ 20.508132] lock(subsys mutex#2); [ 20.508135] lock(&policy->rwsem); [ 20.508138] lock(&bus->mutex); [ 20.508139] [ 20.508139] *** DEADLOCK *** [ 20.508139] [ 20.508141] 3 locks held by swapper/0/1: [ 20.508150] #0: (cpu_hotplug.lock){++++++}, at: [<c000000000087838>] .get_online_cpus+0x48/0xc0 [ 20.508159] #1: (subsys mutex#2){+.+.+.}, at: [<c0000000004d7670>] .subsys_interface_register+0x50/0x110 [ 20.508168] #2: (&policy->rwsem){+.+.+.}, at: [<c00000000068adcc>] .cpufreq_online+0x1ac/0x9d0 [ 20.508169] [ 20.508169] stack backtrace: [ 20.508173] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.8.0-rc7- 00037-gd2ffb01 #21 [ 20.508175] Call Trace: [ 20.508180] [c0000000790c2b90] [c00000000082cc70] .dump_stack+0xe0/0x14c (unreliable) [ 20.508184] [c0000000790c2c20] [c000000000828c88] .print_circular_bug+0x350/0x388 [ 20.508188] [c0000000790c2cd0] [c0000000000ecb0c] .__lock_acquire+0x196c/0x1d30 [ 20.508192] [c0000000790c2e50] [c0000000000ed5b4] .lock_acquire+0x84/0x100 [ 20.508196] [c0000000790c2f20] [c000000000820448] .mutex_lock_nested+0xa8/0x590 [ 20.508201] [c0000000790c3030] [c000000000052830] .pmac_i2c_open+0x30/0x100 [ 20.508206] [c0000000790c30c0] [c000000000052e14] .pmac_i2c_do_begin+0x34/0x120 [ 20.508209] [c0000000790c3150] [c000000000056bc0] .pmf_call_one+0x50/0xd0 [ 20.508213] [c0000000790c31e0] [c00000000068ff1c] .g5_pfunc_switch_volt+0x2c/0xc0 [ 20.508217] [c0000000790c3250] [c00000000068fecc] .g5_pfunc_switch_freq+0x1cc/0x1f0 [ 20.508221] [c0000000790c3320] [c00000000068fc2c] .g5_cpufreq_target+0x2c/0x40 [ 20.508226] [c0000000790c3390] [c0000000006873ec] .__cpufreq_driver_target+0x23c/0x840 [ 20.508230] [c0000000790c3440] [c00000000068c798] .cpufreq_gov_performance_limits+0x18/0x30 [ 20.508235] [c0000000790c34b0] [c00000000068915c] .cpufreq_start_governor+0xac/0x100 [ 20.508239] [c0000000790c3530] [c00000000068a788] .cpufreq_set_policy+0x208/0x260 [ 20.508244] [c0000000790c35d0] [c00000000068abdc] .cpufreq_init_policy+0x6c/0xb0 [ 20.508249] [c0000000790c3940] [c00000000068ae70] .cpufreq_online+0x250/0x9d0 [ 20.508253] [c0000000790c3a30] [c0000000004d76d8] .subsys_interface_register+0xb8/0x110 [ 20.508258] [c0000000790c3ad0] [c000000000689bb0] .cpufreq_register_driver+0x1d0/0x250 [ 20.508262] [c0000000790c3b60] [c000000000b4f8f4] .g5_cpufreq_init+0x9cc/0xa28 [ 20.508267] [c0000000790c3c20] [c00000000000a98c] .do_one_initcall+0x5c/0x1d0 [ 20.508271] [c0000000790c3d00] [c000000000b0f86c] .kernel_init_freeable+0x1ac/0x28c [ 20.508276] [c0000000790c3db0] [c00000000000b3bc] .kernel_init+0x1c/0x140 [ 20.508280] [c0000000790c3e30] [c0000000000098f4] .ret_from_kernel_thread+0x58/0x64 Signed-off-by: Denis Kirjanov <redacted> --- arch/powerpc/platforms/powermac/low_i2c.c | 4 ++++ 1 file changed, 4 insertions(+)diff --git a/arch/powerpc/platforms/powermac/low_i2c.cb/arch/powerpc/platforms/powermac/low_i2c.c index 6d6f277..0159363 100644--- a/arch/powerpc/platforms/powermac/low_i2c.c +++ b/arch/powerpc/platforms/powermac/low_i2c.c@@ -90,6 +90,7 @@ struct pmac_i2c_busint opened; int polled; /* open mode */ struct platform_device *platform_dev; + struct lock_class_key lock_key; /* ops */ int (*open)(struct pmac_i2c_bus *bus);@@ -587,6 +588,7 @@ static void __init kw_i2c_add(structpmac_i2c_host_kw *host, bus->close = kw_i2c_close; bus->xfer = kw_i2c_xfer; mutex_init(&bus->mutex); + lockdep_set_class(&bus->mutex, &bus->lock_key); if (controller == busnode) bus->flags = pmac_i2c_multibus; list_add(&bus->link, &pmac_i2c_busses);@@ -815,6 +817,7 @@ static void __init pmu_i2c_probe(void)bus->hostdata = bus + 1; bus->xfer = pmu_i2c_xfer; mutex_init(&bus->mutex); + lockdep_set_class(&bus->mutex, &bus->lock_key); bus->flags = pmac_i2c_multibus; list_add(&bus->link, &pmac_i2c_busses);@@ -938,6 +941,7 @@ static void __init smu_i2c_probe(void)bus->hostdata = bus + 1; bus->xfer = smu_i2c_xfer; mutex_init(&bus->mutex); + lockdep_set_class(&bus->mutex, &bus->lock_key); bus->flags = 0; list_add(&bus->link, &pmac_i2c_busses); -- 2.4.0