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Date: Tue, 16 Jun 2009 17:39:25 -0700 From: "Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com> To: Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca> Cc: Simon Holm Thøgersen <odie@...aau.dk>, Dave Jones <davej@...hat.com>, Pekka Enberg <penberg@...helsinki.fi>, Dave Young <hidave.darkstar@...il.com>, "Rafael J. Wysocki" <rjw@...k.pl>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, Kernel Testers List <kernel-testers@...r.kernel.org>, "cpufreq@...r.kernel.org" <cpufreq@...r.kernel.org>, Rusty Russell <rusty@...tcorp.com.au>, "trenn@...e.de" <trenn@...e.de>, "sven.wegener@...aler.net" <sven.wegener@...aler.net>, "Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com> Subject: Re: [Bug #13475] suspend/hibernate lockdep warning On Thu, Jun 11, 2009 at 08:23:29AM -0700, Mathieu Desnoyers wrote: > * Simon Holm Thøgersen (odie@...aau.dk) wrote: > > man, 08 06 2009 kl. 10:32 -0400, skrev Dave Jones: > > > On Mon, Jun 08, 2009 at 08:48:45AM -0400, Mathieu Desnoyers wrote: > > > > > > > > > >> Bug-Entry : http://bugzilla.kernel.org/show_bug.cgi?id=13475 > > > > > > >> Subject : suspend/hibernate lockdep warning > > > > > > >> References : http://marc.info/?l=linux-kernel&m=124393723321241&w=4 > > > > > > > > > > > > I suspect the following commit, after revert this patch I test 5 times > > > > > > without lockdep warnings. > > > > > > > > > > > > commit b14893a62c73af0eca414cfed505b8c09efc613c > > > > > > Author: Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca> > > > > > > Date: Sun May 17 10:30:45 2009 -0400 > > > > > > > > > > > > [CPUFREQ] fix timer teardown in ondemand governor > > > > > > > > > > The patch is probably not at fault here. I suspect it's some latent bug > > > > > that simply got exposed by the change to cancel_delayed_work_sync(). In > > > > > any case, Mathieu, can you take a look at this please? > > > > > > > > Yes, it's been looked at and discussed on the cpufreq ML. The short > > > > answer is that they plan to re-engineer cpufreq and remove the policy > > > > rwlock taken around almost every operations at the cpufreq level. > > > > > > > > The short-term solution, which is recognised as ugly, would be do to the > > > > following before doing the cancel_delayed_work_sync() : > > > > > > > > unlock policy rwlock write lock > > > > > > > > lock policy rwlock write lock > > > > > > > > It basically works because this rwlock is unneeded for teardown, hence > > > > the future re-work planned. > > > > > > > > I'm sorry I cannot prepare a patch current... I've got quite a few pages > > > > of Ph.D. thesis due for the beginning of July. > > > > > > I'm kinda scared to touch this code at all for .30 due to the number of > > > unexpected gotchas we seem to run into every time we touch something > > > locking related. So I'm inclined to just live with the lockdep warning > > > for .30, and see how the real fixes look for .31, and push them back > > > as -stable updates if they work out. > > > > Unfortunately I don't think it is just theoretical, I've actually hit > > the following (that haven't got anything to do with suspend/hibernate) > > > > INFO: task cpufreqd:4676 blocked for more than 120 seconds. > > "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. > > cpufreqd D eee2ac60 0 4676 1 > > ee01bd68 00000086 eee2aad0 eee2ac60 00000533 eee2aad0 eee2ac60 0002b16f > > 00000000 eee2ac60 7fffffff 7fffffff eee2ac60 7fffffff 7fffffff 00000000 > > ee01bd70 c03117ee ee01bdbc c0311c0c eee2aad0 eecf6900 eee2aad0 eecf6900 > > Call Trace: > > [<c03117ee>] schedule+0x12/0x24 > > [<c0311c0c>] schedule_timeout+0x17/0x170 > > [<c011a4f7>] ? __wake_up+0x2b/0x51 > > [<c0311afd>] wait_for_common+0xc4/0x135 > > [<c011a694>] ? default_wake_function+0x0/0xd > > [<c0311be0>] wait_for_completion+0x12/0x14 > > [<c012bc6a>] __cancel_work_timer+0xfe/0x129 > > [<c012b635>] ? wq_barrier_func+0x0/0xd > > [<c012bca0>] cancel_delayed_work_sync+0xb/0xd > > [<f20948f9>] cpufreq_governor_dbs+0x22e/0x291 [cpufreq_ondemand] > > [<c02af857>] __cpufreq_governor+0x65/0x9d > > [<c02af960>] __cpufreq_set_policy+0xd1/0x11f > > [<c02b02ae>] store_scaling_governor+0x18a/0x1b2 > > [<c02b09a5>] ? handle_update+0x0/0xd > > [<c02b0124>] ? store_scaling_governor+0x0/0x1b2 > > [<c02b08c9>] store+0x48/0x61 > > [<c01acbf4>] sysfs_write_file+0xb4/0xdf > > [<c01acb40>] ? sysfs_write_file+0x0/0xdf > > [<c0175535>] vfs_write+0x8a/0x104 > > [<c0175648>] sys_write+0x3b/0x60 > > [<c0103110>] sysenter_do_call+0x12/0x2c > > INFO: task kondemand/0:4956 blocked for more than 120 seconds. > > "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. > > kondemand/0 D 00000533 0 4956 2 > > ee1d9efc 00000046 c011815f 00000533 071148de ee1e0080 ee1e0210 00000000 > > c03ff478 9189e633 00000082 c03ff478 ee1e0210 c04159f4 c04159f0 00000000 > > ee1d9f04 c03117ee ee1d9f28 c0313104 ee1d9f30 c04159f4 ee1e0080 c01183be > > Call Trace: > > [<c011815f>] ? update_curr+0x6c/0x14b > > [<c03117ee>] schedule+0x12/0x24 > > [<c0313104>] rwsem_down_failed_common+0x150/0x16e > > [<c01183be>] ? dequeue_task_fair+0x51/0x56 > > [<c031313d>] rwsem_down_write_failed+0x1b/0x23 > > [<c031317e>] call_rwsem_down_write_failed+0x6/0x8 > > [<c03125dd>] ? down_write+0x14/0x16 > > [<c02b0460>] lock_policy_rwsem_write+0x1d/0x33 > > [<f20944aa>] do_dbs_timer+0x45/0x266 [cpufreq_ondemand] > > [<c012b8f7>] worker_thread+0x165/0x212 > > [<f2094465>] ? do_dbs_timer+0x0/0x266 [cpufreq_ondemand] > > [<c012e639>] ? autoremove_wake_function+0x0/0x33 > > [<c012b792>] ? worker_thread+0x0/0x212 > > [<c012e278>] kthread+0x42/0x67 > > [<c012e236>] ? kthread+0x0/0x67 > > [<c01038eb>] kernel_thread_helper+0x7/0x10 > > > > I've only seen it once in 5 boots and CONFIG_PROVELOCKING does not give any > > warnings about this, though it does yell when switching governor as reported > > by others in bug #13493. > > > > Let's hope Mathieu nails it, though I know he's busy with his thesis. > > > > Thanks for the lockdep reports, > > I'm currently looking into it, and it's not pretty. Basically we have : > > A > B > (means B nested in A) > > work > read rwlock policy > > dbs_mutex > work > read rwlock policy > > write rwlock policy > dbs_mutex > > So the added dbs_mutex <- work <- rwlock policy dependency (for proper > teardown) is firing the reverse dependency between policy rwlock and > dbs_mutex. > > The real way to fix this is to do not take the rwlock policy around > non-policy-related actions, like governor START/STOP doing worker > creation/teardown. > > One simple short-term solution would be to take a mutex outside of the > policy rwlock write lock in cpufreq.c. This mutex would be the > equivalent of dbs_mutex "lifted" outside of the rwlock write lock. For > teardown, we only need to hold this mutex, not the rwlock write lock. > Then we can remove the dbs_mutex from the governors. > > But looking at cpufreq.c's cpufreq_add_dev() is very much like kicking a > wasp nest: a lot of error paths are not handled properly, and I fear > someone will have to go through the code, fix the currently incorrect > code paths, and then add the lifted mutex. > > I currently have no time for implementation due to my thesis, but I'll > be happy to review a patch. > How about below patch on top of Mathieu's patch here http://marc.info/?l=linux-kernel&m=124448150529838&w=2 [PATCH] cpufreq: Eliminate lockdep issue with dbs_mutex and policy_rwsem This removes the unneeded dependency of write rwlock policy dbs_mutex dbs_mutex does not have anything to do with timer_init and timer_exit. It is just to protect dbs tunables in sysfs cpufreq/ondemand and is not needed to be held during timer init, exit as well as during governor limit changes. Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@...el.com> --- drivers/cpufreq/cpufreq_ondemand.c | 8 +++----- 1 files changed, 3 insertions(+), 5 deletions(-) diff --git a/drivers/cpufreq/cpufreq_ondemand.c b/drivers/cpufreq/cpufreq_ondemand.c index e741c33..1c94ff5 100644 --- a/drivers/cpufreq/cpufreq_ondemand.c +++ b/drivers/cpufreq/cpufreq_ondemand.c @@ -352,8 +352,8 @@ static ssize_t store_powersave_bias(struct cpufreq_policy *unused, mutex_lock(&dbs_mutex); dbs_tuners_ins.powersave_bias = input; - ondemand_powersave_bias_init(); mutex_unlock(&dbs_mutex); + ondemand_powersave_bias_init(); return count; } @@ -626,14 +626,14 @@ static int cpufreq_governor_dbs(struct cpufreq_policy *policy, dbs_tuners_ins.sampling_rate = def_sampling_rate; } + mutex_unlock(&dbs_mutex); dbs_timer_init(this_dbs_info); - mutex_unlock(&dbs_mutex); break; case CPUFREQ_GOV_STOP: - mutex_lock(&dbs_mutex); dbs_timer_exit(this_dbs_info); + mutex_lock(&dbs_mutex); sysfs_remove_group(&policy->kobj, &dbs_attr_group); dbs_enable--; mutex_unlock(&dbs_mutex); @@ -641,14 +641,12 @@ static int cpufreq_governor_dbs(struct cpufreq_policy *policy, break; case CPUFREQ_GOV_LIMITS: - mutex_lock(&dbs_mutex); if (policy->max < this_dbs_info->cur_policy->cur) __cpufreq_driver_target(this_dbs_info->cur_policy, policy->max, CPUFREQ_RELATION_H); else if (policy->min > this_dbs_info->cur_policy->cur) __cpufreq_driver_target(this_dbs_info->cur_policy, policy->min, CPUFREQ_RELATION_L); - mutex_unlock(&dbs_mutex); break; } return 0; -- 1.6.0.6 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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