Re: [PATCH V2 0/7] cpufreq: governors: Fix ABBA lockups

[Viresh Kumar <viresh.kumar@linaro.org>]

On 03-02-16, 21:40, Viresh Kumar wrote:
> On 03-02-16, 15:54, Juri Lelli wrote:
> > Ouch, I've just got this executing -f basic on Juno. :(
> > It happens with the hotplug_1_by_1 test.
> > 
> > 
> > [ 1086.531252] IRQ1 no longer affine to CPU1
> > [ 1086.531495] CPU1: shutdown
> > [ 1086.538199] psci: CPU1 killed.
> > [ 1086.583396]
> > [ 1086.584881] ======================================================
> > [ 1086.590999] [ INFO: possible circular locking dependency detected ]
> > [ 1086.597205] 4.5.0-rc2+ #37 Not tainted
> > [ 1086.600914] -------------------------------------------------------
> > [ 1086.607118] runme.sh/1052 is trying to acquire lock:
> > [ 1086.612031]  (sb_writers#7){.+.+.+}, at: [<ffffffc000249500>] __sb_start_write+0xcc/0xe0
> > [ 1086.620090]
> > [ 1086.620090] but task is already holding lock:
> > [ 1086.625865]  (&policy->rwsem){+++++.}, at: [<ffffffc0005c8ee4>] cpufreq_offline+0x7c/0x278
> > [ 1086.634081]
> > [ 1086.634081] which lock already depends on the new lock.
> > [ 1086.634081]
> > [ 1086.642180]
> > [ 1086.642180] the existing dependency chain (in reverse order) is:
> > [ 1086.649589]
> > -> #1 (&policy->rwsem){+++++.}:
> > [ 1086.653929]        [<ffffffc00011d9a4>] check_prev_add+0x670/0x754
> > [ 1086.660060]        [<ffffffc00011e1ac>] validate_chain.isra.36+0x724/0xa0c
> > [ 1086.666876]        [<ffffffc00011f904>] __lock_acquire+0x4e4/0xba0
> > [ 1086.673001]        [<ffffffc000120b58>] lock_release+0x244/0x570
> > [ 1086.678955]        [<ffffffc0007351d0>] __mutex_unlock_slowpath+0xa0/0x18c
> > [ 1086.685771]        [<ffffffc0007352dc>] mutex_unlock+0x20/0x2c
> > [ 1086.691553]        [<ffffffc0002ccd24>] kernfs_fop_write+0xb0/0x194
> > [ 1086.697768]        [<ffffffc00024478c>] __vfs_write+0x48/0x104
> > [ 1086.703550]        [<ffffffc0002457a4>] vfs_write+0x98/0x198
> > [ 1086.709161]        [<ffffffc0002465e4>] SyS_write+0x54/0xb0
> > [ 1086.714684]        [<ffffffc000085d30>] el0_svc_naked+0x24/0x28
> > [ 1086.720555]
> > -> #0 (sb_writers#7){.+.+.+}:
> > [ 1086.724730]        [<ffffffc00011c574>] print_circular_bug+0x80/0x2e4
> > [ 1086.731116]        [<ffffffc00011d470>] check_prev_add+0x13c/0x754
> > [ 1086.737243]        [<ffffffc00011e1ac>] validate_chain.isra.36+0x724/0xa0c
> > [ 1086.744059]        [<ffffffc00011f904>] __lock_acquire+0x4e4/0xba0
> > [ 1086.750184]        [<ffffffc0001207f4>] lock_acquire+0xe4/0x204
> > [ 1086.756052]        [<ffffffc000118da0>] percpu_down_read+0x50/0xe4
> > [ 1086.762180]        [<ffffffc000249500>] __sb_start_write+0xcc/0xe0
> > [ 1086.768306]        [<ffffffc00026ae90>] mnt_want_write+0x28/0x54
> > [ 1086.774263]        [<ffffffc0002555f8>] do_last+0x660/0xcb8
> > [ 1086.779788]        [<ffffffc000255cdc>] path_openat+0x8c/0x2b0
> > [ 1086.785570]        [<ffffffc000256fbc>] do_filp_open+0x78/0xf0
> > [ 1086.791353]        [<ffffffc000244058>] do_sys_open+0x150/0x214
> > [ 1086.797222]        [<ffffffc0002441a0>] SyS_openat+0x3c/0x48
> > [ 1086.802831]        [<ffffffc000085d30>] el0_svc_naked+0x24/0x28
> > [ 1086.808700]
> > [ 1086.808700] other info that might help us debug this:
> > [ 1086.808700]
> > [ 1086.816627]  Possible unsafe locking scenario:
> > [ 1086.816627]
> > [ 1086.822488]        CPU0                    CPU1
> > [ 1086.826971]        ----                    ----
> > [ 1086.831453]   lock(&policy->rwsem);
> > [ 1086.834918]                                lock(sb_writers#7);
> > [ 1086.840713]                                lock(&policy->rwsem);
> > [ 1086.846671]   lock(sb_writers#7);
> > [ 1086.849972]
> > [ 1086.849972]  *** DEADLOCK ***
> > [ 1086.849972]
> > [ 1086.855836] 1 lock held by runme.sh/1052:
> > [ 1086.859802]  #0:  (&policy->rwsem){+++++.}, at: [<ffffffc0005c8ee4>] cpufreq_offline+0x7c/0x278
> > [ 1086.868453]
> > [ 1086.868453] stack backtrace:
> > [ 1086.872769] CPU: 5 PID: 1052 Comm: runme.sh Not tainted 4.5.0-rc2+ #37
> > [ 1086.879229] Hardware name: ARM Juno development board (r2) (DT)
> > [ 1086.885089] Call trace:
> > [ 1086.887511] [<ffffffc00008a788>] dump_backtrace+0x0/0x1f4
> > [ 1086.892858] [<ffffffc00008a99c>] show_stack+0x20/0x28
> > [ 1086.897861] [<ffffffc00041a380>] dump_stack+0x84/0xc0
> > [ 1086.902863] [<ffffffc00011c6c8>] print_circular_bug+0x1d4/0x2e4
> > [ 1086.908725] [<ffffffc00011d470>] check_prev_add+0x13c/0x754
> > [ 1086.914244] [<ffffffc00011e1ac>] validate_chain.isra.36+0x724/0xa0c
> > [ 1086.920448] [<ffffffc00011f904>] __lock_acquire+0x4e4/0xba0
> > [ 1086.925965] [<ffffffc0001207f4>] lock_acquire+0xe4/0x204
> > [ 1086.931224] [<ffffffc000118da0>] percpu_down_read+0x50/0xe4
> > [ 1086.936742] [<ffffffc000249500>] __sb_start_write+0xcc/0xe0
> > [ 1086.942260] [<ffffffc00026ae90>] mnt_want_write+0x28/0x54
> > [ 1086.947605] [<ffffffc0002555f8>] do_last+0x660/0xcb8
> > [ 1086.952520] [<ffffffc000255cdc>] path_openat+0x8c/0x2b0
> > [ 1086.957693] [<ffffffc000256fbc>] do_filp_open+0x78/0xf0
> > [ 1086.962865] [<ffffffc000244058>] do_sys_open+0x150/0x214
> > [ 1086.968123] [<ffffffc0002441a0>] SyS_openat+0x3c/0x48
> > [ 1086.973124] [<ffffffc000085d30>] el0_svc_naked+0x24/0x28
> > [ 1087.019315] Detected PIPT I-cache on CPU1
> > [ 1087.019373] CPU1: Booted secondary processor [410fd080]
> 
> Urg..

Urg square :(

> I failed to understand it for now though. Please test only the first 4
> patches and leave the bottom three. AFAICT, this is caused by the 6th
> patch.

>From the code I still failed to understand this since sometime back
and I something just caught my eyes and the 6th patch needs this
fixup:

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index 7bc8a5ed97e5..ac3348ecde7b 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -1351,7 +1351,7 @@ static void cpufreq_offline(unsigned int cpu)
                                pr_err("%s: Failed to start governor\n", __func__);
                }
 
-               return;
+               goto unlock;
        }
 
        if (cpufreq_driver->stop_cpu)
@@ -1373,6 +1373,8 @@ static void cpufreq_offline(unsigned int cpu)
                cpufreq_driver->exit(policy);
                policy->freq_table = NULL;
        }
+
+unlock:
        up_write(&policy->rwsem);
 }

I tried the basic tests using './runme' and they aren't reporting the
same lockdep now. And yes, your lockdep occurred on my exynos board as
well :)

I have re-pushed my patches again to the same branch. All 7 look fine
to me now :)

-- 
viresh