From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from gate.crashing.org (gate.crashing.org [63.228.1.57]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 3sjbzz61cWzDrM1 for ; Tue, 27 Sep 2016 07:03:59 +1000 (AEST) Message-ID: <1474923820.2857.253.camel@kernel.crashing.org> Subject: Re: [PATCH] i2c_powermac: shut up lockdep warning From: Benjamin Herrenschmidt To: Denis Kirjanov , "linuxppc-dev@lists.ozlabs.org" Date: Tue, 27 Sep 2016 07:03:40 +1000 In-Reply-To: References: <1474457698-3855-1-git-send-email-kda@linux-powerpc.org> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Mon, 2016-09-26 at 14:00 +0300, Denis Kirjanov wrote: > > > On Wednesday, September 21, 2016, Denis Kirjanov 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: [] > > .pmac_i2c_open+0x30/0x100 > > [   20.507819] > > [   20.507819] but task is already holding lock: > > [   20.507829]  (&policy->rwsem){+.+.+.}, at: [] > > .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]        [] .down_write+0x6c/0x110 > > [   20.507849]        [] > > .cpufreq_online+0x1ac/0x9d0 > > [   20.507855]        [] > > .subsys_interface_register+0xb8/0x110 > > [   20.507860]        [] > > .cpufreq_register_driver+0x1d0/0x250 > > [   20.507866]        [] > > .g5_cpufreq_init+0x9cc/0xa28 > > [   20.507872]        [] > > .do_one_initcall+0x5c/0x1d0 > > [   20.507878]        [] > > .kernel_init_freeable+0x1ac/0x28c > > [   20.507883]        [] .kernel_init+0x1c/0x140 > > [   20.507887]        [] > > .ret_from_kernel_thread+0x58/0x64 > > [   20.507894] > > [   20.507894] -> #3 (subsys mutex#2){+.+.+.}: > > [   20.507899]        [] > > .mutex_lock_nested+0xa8/0x590 > > [   20.507903]        [] > > .bus_probe_device+0x44/0xe0 > > [   20.507907]        [] .device_add+0x508/0x730 > > [   20.507911]        [] > > .register_cpu+0x118/0x190 > > [   20.507916]        [] > > .topology_init+0x148/0x248 > > [   20.507921]        [] > > .do_one_initcall+0x5c/0x1d0 > > [   20.507925]        [] > > .kernel_init_freeable+0x1ac/0x28c > > [   20.507929]        [] .kernel_init+0x1c/0x140 > > [   20.507934]        [] > > .ret_from_kernel_thread+0x58/0x64 > > [   20.507939] > > [   20.507939] -> #2 (cpu_add_remove_lock){+.+.+.}: > > [   20.507944]        [] > > .mutex_lock_nested+0xa8/0x590 > > [   20.507950]        [] > > .register_cpu_notifier+0x2c/0x70 > > [   20.507955]        [] > > .spawn_ksoftirqd+0x18/0x4c > > [   20.507959]        [] > > .do_one_initcall+0x5c/0x1d0 > > [   20.507964]        [] > > .kernel_init_freeable+0xb0/0x28c > > [   20.507968]        [] .kernel_init+0x1c/0x140 > > [   20.507972]        [] > > .ret_from_kernel_thread+0x58/0x64 > > [   20.507978] > > [   20.507978] -> #1 (&host->mutex){+.+.+.}: > > [   20.507982]        [] > > .mutex_lock_nested+0xa8/0x590 > > [   20.507987]        [] .kw_i2c_open+0x18/0x30 > > [   20.507991]        [] > > .pmac_i2c_open+0x94/0x100 > > [   20.507995]        [] > > .smp_core99_probe+0x260/0x410 > > [   20.507999]        [] > > .smp_prepare_cpus+0x280/0x2ac > > [   20.508003]        [] > > .kernel_init_freeable+0x88/0x28c > > [   20.508008]        [] .kernel_init+0x1c/0x140 > > [   20.508012]        [] > > .ret_from_kernel_thread+0x58/0x64 > > [   20.508018] > > [   20.508018] -> #0 (&bus->mutex){+.+.+.}: > > [   20.508023]        [] .lock_acquire+0x84/0x100 > > [   20.508027]        [] > > .mutex_lock_nested+0xa8/0x590 > > [   20.508032]        [] > > .pmac_i2c_open+0x30/0x100 > > [   20.508037]        [] > > .pmac_i2c_do_begin+0x34/0x120 > > [   20.508040]        [] .pmf_call_one+0x50/0xd0 > > [   20.508045]        [] > > .g5_pfunc_switch_volt+0x2c/0xc0 > > [   20.508050]        [] > > .g5_pfunc_switch_freq+0x1cc/0x1f0 > > [   20.508054]        [] > > .g5_cpufreq_target+0x2c/0x40 > > [   20.508058]        [] > > .__cpufreq_driver_target+0x23c/0x840 > > [   20.508062]        [] > > .cpufreq_gov_performance_limits+0x18/0x30 > > [   20.508067]        [] > > .cpufreq_start_governor+0xac/0x100 > > [   20.508071]        [] > > .cpufreq_set_policy+0x208/0x260 > > [   20.508076]        [] > > .cpufreq_init_policy+0x6c/0xb0 > > [   20.508081]        [] > > .cpufreq_online+0x250/0x9d0 > > [   20.508085]        [] > > .subsys_interface_register+0xb8/0x110 > > [   20.508090]        [] > > .cpufreq_register_driver+0x1d0/0x250 > > [   20.508094]        [] > > .g5_cpufreq_init+0x9cc/0xa28 > > [   20.508099]        [] > > .do_one_initcall+0x5c/0x1d0 > > [   20.508103]        [] > > .kernel_init_freeable+0x1ac/0x28c > > [   20.508107]        [] .kernel_init+0x1c/0x140 > > [   20.508112]        [] > > .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: > > [] .get_online_cpus+0x48/0xc0 > > [   20.508159]  #1:  (subsys mutex#2){+.+.+.}, at: > > [] .subsys_interface_register+0x50/0x110 > > [   20.508168]  #2:  (&policy->rwsem){+.+.+.}, at: > > [] .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 > > --- > >  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 > > > >