Subject: Re: [PATCH] i2c_powermac: shut up lockdep warning

From: Benjamin Herrenschmidt <[email-masked]>
Date: Tue, 27 Sep 2016 07:03:40 +1000

On Mon, 2016-09-26 at 14:00 +0300, Denis Kirjanov wrote:
> 
> 
> On Wednesday, September 21, 2016, Denis Kirjanov <[email-masked]
> rg> wrote:
> > That's unclear why lockdep shows the following warning but adding a
> > lockdep class to struct pmac_i2c_bus solves it
> 
> HI 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!
> > 
> > [   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 <[email-masked]>
> > ---
> >  arch/powerpc/platforms/powermac/low_i2c.c | 4 ++++
> >  1 file changed, 4 insertions(+)
> > 
> > diff --git a/arch/powerpc/platforms/powermac/low_i2c.c
> > b/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_bus
> >         int                     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(struct
> > pmac_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
> > 
> >