<br><br>On Wednesday, September 21, 2016, Denis Kirjanov <<a href="mailto:kda@linux-powerpc.org">kda@linux-powerpc.org</a>> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">That's unclear why lockdep shows the following warning but adding a<br>
lockdep class to struct pmac_i2c_bus solves it</blockquote><div><br></div><div>HI Ben, </div><div><br></div><div>could you give any comments on this? </div><div><br></div><div>Thanks!</div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<br>
[ 20.507795] ==============================<wbr>========================<br>
[ 20.507796] [ INFO: possible circular locking dependency detected ]<br>
[ 20.507800] 4.8.0-rc7-00037-gd2ffb01 #21 Not tainted<br>
[ 20.507801] ------------------------------<wbr>-------------------------<br>
[ 20.507803] swapper/0/1 is trying to acquire lock:<br>
[ 20.507818] (&bus->mutex){+.+.+.}, at: [<c000000000052830>] .pmac_i2c_open+0x30/0x100<br>
[ 20.507819]<br>
[ 20.507819] but task is already holding lock:<br>
[ 20.507829] (&policy->rwsem){+.+.+.}, at: [<c00000000068adcc>] .cpufreq_online+0x1ac/0x9d0<br>
[ 20.507830]<br>
[ 20.507830] which lock already depends on the new lock.<br>
[ 20.507830]<br>
[ 20.507832]<br>
[ 20.507832] the existing dependency chain (in reverse order) is:<br>
[ 20.507837]<br>
[ 20.507837] -> #4 (&policy->rwsem){+.+.+.}:<br>
[ 20.507844] [<c00000000082385c>] .down_write+0x6c/0x110<br>
[ 20.507849] [<c00000000068adcc>] .cpufreq_online+0x1ac/0x9d0<br>
[ 20.507855] [<c0000000004d76d8>] .subsys_interface_register+<wbr>0xb8/0x110<br>
[ 20.507860] [<c000000000689bb0>] .cpufreq_register_driver+<wbr>0x1d0/0x250<br>
[ 20.507866] [<c000000000b4f8f4>] .g5_cpufreq_init+0x9cc/0xa28<br>
[ 20.507872] [<c00000000000a98c>] .do_one_initcall+0x5c/0x1d0<br>
[ 20.507878] [<c000000000b0f86c>] .kernel_init_freeable+0x1ac/<wbr>0x28c<br>
[ 20.507883] [<c00000000000b3bc>] .kernel_init+0x1c/0x140<br>
[ 20.507887] [<c0000000000098f4>] .ret_from_kernel_thread+0x58/<wbr>0x64<br>
[ 20.507894]<br>
[ 20.507894] -> #3 (subsys mutex#2){+.+.+.}:<br>
[ 20.507899] [<c000000000820448>] .mutex_lock_nested+0xa8/0x590<br>
[ 20.507903] [<c0000000004d7f24>] .bus_probe_device+0x44/0xe0<br>
[ 20.507907] [<c0000000004d5208>] .device_add+0x508/0x730<br>
[ 20.507911] [<c0000000004dd528>] .register_cpu+0x118/0x190<br>
[ 20.507916] [<c000000000b14450>] .topology_init+0x148/0x248<br>
[ 20.507921] [<c00000000000a98c>] .do_one_initcall+0x5c/0x1d0<br>
[ 20.507925] [<c000000000b0f86c>] .kernel_init_freeable+0x1ac/<wbr>0x28c<br>
[ 20.507929] [<c00000000000b3bc>] .kernel_init+0x1c/0x140<br>
[ 20.507934] [<c0000000000098f4>] .ret_from_kernel_thread+0x58/<wbr>0x64<br>
[ 20.507939]<br>
[ 20.507939] -> #2 (cpu_add_remove_lock){+.+.+.}:<br>
[ 20.507944] [<c000000000820448>] .mutex_lock_nested+0xa8/0x590<br>
[ 20.507950] [<c000000000087a9c>] .register_cpu_notifier+0x2c/<wbr>0x70<br>
[ 20.507955] [<c000000000b267e0>] .spawn_ksoftirqd+0x18/0x4c<br>
[ 20.507959] [<c00000000000a98c>] .do_one_initcall+0x5c/0x1d0<br>
[ 20.507964] [<c000000000b0f770>] .kernel_init_freeable+0xb0/<wbr>0x28c<br>
[ 20.507968] [<c00000000000b3bc>] .kernel_init+0x1c/0x140<br>
[ 20.507972] [<c0000000000098f4>] .ret_from_kernel_thread+0x58/<wbr>0x64<br>
[ 20.507978]<br>
[ 20.507978] -> #1 (&host->mutex){+.+.+.}:<br>
[ 20.507982] [<c000000000820448>] .mutex_lock_nested+0xa8/0x590<br>
[ 20.507987] [<c0000000000527e8>] .kw_i2c_open+0x18/0x30<br>
[ 20.507991] [<c000000000052894>] .pmac_i2c_open+0x94/0x100<br>
[ 20.507995] [<c000000000b220a0>] .smp_core99_probe+0x260/0x410<br>
[ 20.507999] [<c000000000b185bc>] .smp_prepare_cpus+0x280/0x2ac<br>
[ 20.508003] [<c000000000b0f748>] .kernel_init_freeable+0x88/<wbr>0x28c<br>
[ 20.508008] [<c00000000000b3bc>] .kernel_init+0x1c/0x140<br>
[ 20.508012] [<c0000000000098f4>] .ret_from_kernel_thread+0x58/<wbr>0x64<br>
[ 20.508018]<br>
[ 20.508018] -> #0 (&bus->mutex){+.+.+.}:<br>
[ 20.508023] [<c0000000000ed5b4>] .lock_acquire+0x84/0x100<br>
[ 20.508027] [<c000000000820448>] .mutex_lock_nested+0xa8/0x590<br>
[ 20.508032] [<c000000000052830>] .pmac_i2c_open+0x30/0x100<br>
[ 20.508037] [<c000000000052e14>] .pmac_i2c_do_begin+0x34/0x120<br>
[ 20.508040] [<c000000000056bc0>] .pmf_call_one+0x50/0xd0<br>
[ 20.508045] [<c00000000068ff1c>] .g5_pfunc_switch_volt+0x2c/<wbr>0xc0<br>
[ 20.508050] [<c00000000068fecc>] .g5_pfunc_switch_freq+0x1cc/<wbr>0x1f0<br>
[ 20.508054] [<c00000000068fc2c>] .g5_cpufreq_target+0x2c/0x40<br>
[ 20.508058] [<c0000000006873ec>] .__cpufreq_driver_target+<wbr>0x23c/0x840<br>
[ 20.508062] [<c00000000068c798>] .cpufreq_gov_performance_<wbr>limits+0x18/0x30<br>
[ 20.508067] [<c00000000068915c>] .cpufreq_start_governor+0xac/<wbr>0x100<br>
[ 20.508071] [<c00000000068a788>] .cpufreq_set_policy+0x208/<wbr>0x260<br>
[ 20.508076] [<c00000000068abdc>] .cpufreq_init_policy+0x6c/0xb0<br>
[ 20.508081] [<c00000000068ae70>] .cpufreq_online+0x250/0x9d0<br>
[ 20.508085] [<c0000000004d76d8>] .subsys_interface_register+<wbr>0xb8/0x110<br>
[ 20.508090] [<c000000000689bb0>] .cpufreq_register_driver+<wbr>0x1d0/0x250<br>
[ 20.508094] [<c000000000b4f8f4>] .g5_cpufreq_init+0x9cc/0xa28<br>
[ 20.508099] [<c00000000000a98c>] .do_one_initcall+0x5c/0x1d0<br>
[ 20.508103] [<c000000000b0f86c>] .kernel_init_freeable+0x1ac/<wbr>0x28c<br>
[ 20.508107] [<c00000000000b3bc>] .kernel_init+0x1c/0x140<br>
[ 20.508112] [<c0000000000098f4>] .ret_from_kernel_thread+0x58/<wbr>0x64<br>
[ 20.508113]<br>
[ 20.508113] other info that might help us debug this:<br>
[ 20.508113]<br>
[ 20.508121] Chain exists of:<br>
[ 20.508121] &bus->mutex --> subsys mutex#2 --> &policy->rwsem<br>
[ 20.508121]<br>
[ 20.508123] Possible unsafe locking scenario:<br>
[ 20.508123]<br>
[ 20.508124] CPU0 CPU1<br>
[ 20.508125] ---- ----<br>
[ 20.508128] lock(&policy->rwsem);<br>
[ 20.508132] lock(subsys mutex#2);<br>
[ 20.508135] lock(&policy->rwsem);<br>
[ 20.508138] lock(&bus->mutex);<br>
[ 20.508139]<br>
[ 20.508139] *** DEADLOCK ***<br>
[ 20.508139]<br>
[ 20.508141] 3 locks held by swapper/0/1:<br>
[ 20.508150] #0: (cpu_hotplug.lock){++++++}, at: [<c000000000087838>] .get_online_cpus+0x48/0xc0<br>
[ 20.508159] #1: (subsys mutex#2){+.+.+.}, at: [<c0000000004d7670>] .subsys_interface_register+<wbr>0x50/0x110<br>
[ 20.508168] #2: (&policy->rwsem){+.+.+.}, at: [<c00000000068adcc>] .cpufreq_online+0x1ac/0x9d0<br>
[ 20.508169]<br>
[ 20.508169] stack backtrace:<br>
[ 20.508173] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.8.0-rc7-00037-gd2ffb01 #21<br>
[ 20.508175] Call Trace:<br>
[ 20.508180] [c0000000790c2b90] [c00000000082cc70] .dump_stack+0xe0/0x14c (unreliable)<br>
[ 20.508184] [c0000000790c2c20] [c000000000828c88] .print_circular_bug+0x350/<wbr>0x388<br>
[ 20.508188] [c0000000790c2cd0] [c0000000000ecb0c] .__lock_acquire+0x196c/0x1d30<br>
[ 20.508192] [c0000000790c2e50] [c0000000000ed5b4] .lock_acquire+0x84/0x100<br>
[ 20.508196] [c0000000790c2f20] [c000000000820448] .mutex_lock_nested+0xa8/0x590<br>
[ 20.508201] [c0000000790c3030] [c000000000052830] .pmac_i2c_open+0x30/0x100<br>
[ 20.508206] [c0000000790c30c0] [c000000000052e14] .pmac_i2c_do_begin+0x34/0x120<br>
[ 20.508209] [c0000000790c3150] [c000000000056bc0] .pmf_call_one+0x50/0xd0<br>
[ 20.508213] [c0000000790c31e0] [c00000000068ff1c] .g5_pfunc_switch_volt+0x2c/<wbr>0xc0<br>
[ 20.508217] [c0000000790c3250] [c00000000068fecc] .g5_pfunc_switch_freq+0x1cc/<wbr>0x1f0<br>
[ 20.508221] [c0000000790c3320] [c00000000068fc2c] .g5_cpufreq_target+0x2c/0x40<br>
[ 20.508226] [c0000000790c3390] [c0000000006873ec] .__cpufreq_driver_target+<wbr>0x23c/0x840<br>
[ 20.508230] [c0000000790c3440] [c00000000068c798] .cpufreq_gov_performance_<wbr>limits+0x18/0x30<br>
[ 20.508235] [c0000000790c34b0] [c00000000068915c] .cpufreq_start_governor+0xac/<wbr>0x100<br>
[ 20.508239] [c0000000790c3530] [c00000000068a788] .cpufreq_set_policy+0x208/<wbr>0x260<br>
[ 20.508244] [c0000000790c35d0] [c00000000068abdc] .cpufreq_init_policy+0x6c/0xb0<br>
[ 20.508249] [c0000000790c3940] [c00000000068ae70] .cpufreq_online+0x250/0x9d0<br>
[ 20.508253] [c0000000790c3a30] [c0000000004d76d8] .subsys_interface_register+<wbr>0xb8/0x110<br>
[ 20.508258] [c0000000790c3ad0] [c000000000689bb0] .cpufreq_register_driver+<wbr>0x1d0/0x250<br>
[ 20.508262] [c0000000790c3b60] [c000000000b4f8f4] .g5_cpufreq_init+0x9cc/0xa28<br>
[ 20.508267] [c0000000790c3c20] [c00000000000a98c] .do_one_initcall+0x5c/0x1d0<br>
[ 20.508271] [c0000000790c3d00] [c000000000b0f86c] .kernel_init_freeable+0x1ac/<wbr>0x28c<br>
[ 20.508276] [c0000000790c3db0] [c00000000000b3bc] .kernel_init+0x1c/0x140<br>
[ 20.508280] [c0000000790c3e30] [c0000000000098f4] .ret_from_kernel_thread+0x58/<wbr>0x64<br>
<br>
Signed-off-by: Denis Kirjanov <<a href="javascript:;" onclick="_e(event, 'cvml', 'kda@linux-powerpc.org')">kda@linux-powerpc.org</a>><br>
---<br>
arch/powerpc/platforms/<wbr>powermac/low_i2c.c | 4 ++++<br>
1 file changed, 4 insertions(+)<br>
<br>
diff --git a/arch/powerpc/platforms/<wbr>powermac/low_i2c.c b/arch/powerpc/platforms/<wbr>powermac/low_i2c.c<br>
index 6d6f277..0159363 100644<br>
--- a/arch/powerpc/platforms/<wbr>powermac/low_i2c.c<br>
+++ b/arch/powerpc/platforms/<wbr>powermac/low_i2c.c<br>
@@ -90,6 +90,7 @@ struct pmac_i2c_bus<br>
int opened;<br>
int polled; /* open mode */<br>
struct platform_device *platform_dev;<br>
+ struct lock_class_key lock_key;<br>
<br>
/* ops */<br>
int (*open)(struct pmac_i2c_bus *bus);<br>
@@ -587,6 +588,7 @@ static void __init kw_i2c_add(struct pmac_i2c_host_kw *host,<br>
bus->close = kw_i2c_close;<br>
bus->xfer = kw_i2c_xfer;<br>
mutex_init(&bus->mutex);<br>
+ lockdep_set_class(&bus->mutex, &bus->lock_key);<br>
if (controller == busnode)<br>
bus->flags = pmac_i2c_multibus;<br>
list_add(&bus->link, &pmac_i2c_busses);<br>
@@ -815,6 +817,7 @@ static void __init pmu_i2c_probe(void)<br>
bus->hostdata = bus + 1;<br>
bus->xfer = pmu_i2c_xfer;<br>
mutex_init(&bus->mutex);<br>
+ lockdep_set_class(&bus->mutex, &bus->lock_key);<br>
bus->flags = pmac_i2c_multibus;<br>
list_add(&bus->link, &pmac_i2c_busses);<br>
<br>
@@ -938,6 +941,7 @@ static void __init smu_i2c_probe(void)<br>
bus->hostdata = bus + 1;<br>
bus->xfer = smu_i2c_xfer;<br>
mutex_init(&bus->mutex);<br>
+ lockdep_set_class(&bus->mutex, &bus->lock_key);<br>
bus->flags = 0;<br>
list_add(&bus->link, &pmac_i2c_busses);<br>
<br>
--<br>
2.4.0<br>
<br>
</blockquote>