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SubjectRe: [PATCH] cpufreq: remove dbs_mutex

* Ingo Molnar <mingo@elte.hu> wrote:

> * Thomas Renninger <trenn@suse.de> wrote:
>
> > > Note, this bug warning still triggers rather frequently with
> > > latest -git (fb20871) during bootup on two test-systems -
> > > relevant portion of the bootlog attached below. As usual i can
> > > test any fix for this.
> >
> > Best rip out the dbs_mutex in drivers/cpufreq/cpufreq_ondemand.c
> > totally. I can provide several locking cleanups for cpufreq for
> > .31 the next days, including dbs_mutex removal, which I think is
> > not needed. The dbs_mutex removal which should fix this could then
> > be marked: CC: stable@kernel.org
>
> drivers/cpufreq/cpufreq_conservative.c too i guess?
>
> Something like the patch below?
>
> Utterly untested and such.

i tested it and this blatant blind ripping out of a layer of locking
uncovered the next layer:

[ 144.961483] =======================================================
[ 144.961685] [ INFO: possible circular locking dependency detected ]
[ 144.961785] 2.6.30-tip-08973-gb747c8d-dirty #6295
[ 144.961878] -------------------------------------------------------
[ 144.961974] S99local/8461 is trying to acquire lock:
[ 144.962016] (&(&dbs_info->work)->work){+.+...}, at: [<c109962a>] wait_on_work+0x0/0xba
[ 144.962016]
[ 144.962016] but task is already holding lock:
[ 144.962016] (&per_cpu(cpu_policy_rwsem, cpu)){+++++.}, at: [<c1f5dd3f>] lock_policy_rwsem_write+0x73/0xec
[ 144.962016]
[ 144.962016] which lock already depends on the new lock.

(see below for the full details)

I guess someone who knows the cpufreq code will have to fix the
locking in this code for real.

Ingo

[ 144.767335] CPUFREQ: ondemand sampling_rate_max sysfs file is deprecated - used by: cat
[ 144.961480]
[ 144.961483] =======================================================
[ 144.961685] [ INFO: possible circular locking dependency detected ]
[ 144.961785] 2.6.30-tip-08973-gb747c8d-dirty #6295
[ 144.961878] -------------------------------------------------------
[ 144.961974] S99local/8461 is trying to acquire lock:
[ 144.962016] (&(&dbs_info->work)->work){+.+...}, at: [<c109962a>] wait_on_work+0x0/0xba
[ 144.962016]
[ 144.962016] but task is already holding lock:
[ 144.962016] (&per_cpu(cpu_policy_rwsem, cpu)){+++++.}, at: [<c1f5dd3f>] lock_policy_rwsem_write+0x73/0xec
[ 144.962016]
[ 144.962016] which lock already depends on the new lock.
[ 144.962016]
[ 144.962016]
[ 144.962016] the existing dependency chain (in reverse order) is:
[ 144.962016]
[ 144.962016] -> #1 (&per_cpu(cpu_policy_rwsem, cpu)){+++++.}:
[ 144.962016] [<c10bcd0d>] check_prev_add+0xf0/0x151
[ 144.962016] [<c10bcdd3>] check_prevs_add+0x65/0xbf
[ 144.962016] [<c10bce9e>] validate_chain+0x71/0x99
[ 144.962016] [<c10bd184>] __lock_acquire+0x2be/0x33d
[ 144.962016] [<c10bd27f>] lock_acquire+0x7c/0x9f
[ 144.962016] [<c23b1b36>] down_write+0x32/0x95
[ 144.962016] [<c1f5dd3f>] lock_policy_rwsem_write+0x73/0xec
[ 144.962016] [<c1f627cd>] do_dbs_timer+0x50/0x160
[ 144.962016] [<c1098de1>] run_workqueue+0xec/0x243
[ 144.962016] [<c109badf>] worker_thread+0x13b/0x14c
[ 144.962016] [<c10a05ed>] kthread+0x89/0x92
[ 144.962016] [<c10064a7>] kernel_thread_helper+0x7/0x10
[ 144.962016] [<ffffffff>] 0xffffffff
[ 144.962016]
[ 144.962016] -> #0 (&(&dbs_info->work)->work){+.+...}:
[ 144.962016] [<c10bcc50>] check_prev_add+0x33/0x151
[ 144.962016] [<c10bcdd3>] check_prevs_add+0x65/0xbf
[ 144.962016] [<c10bce9e>] validate_chain+0x71/0x99
[ 144.962016] [<c10bd184>] __lock_acquire+0x2be/0x33d
[ 144.962016] [<c10bd27f>] lock_acquire+0x7c/0x9f
[ 144.962016] [<c1099662>] wait_on_work+0x38/0xba
[ 144.962016] [<c109975c>] __cancel_work_timer+0x78/0x99
[ 144.962016] [<c109978d>] cancel_delayed_work_sync+0x10/0x12
[ 144.962016] [<c1f62710>] dbs_timer_exit+0x17/0x19
[ 144.962016] [<c1f62d68>] cpufreq_governor_dbs+0x23f/0x2df
[ 144.962016] [<c1f5e7cb>] __cpufreq_governor+0x9a/0xde
[ 144.962016] [<c1f5ea3c>] __cpufreq_set_policy+0x22d/0x2fa
[ 144.967630] [<c1f5ebce>] store_scaling_governor+0xc5/0x108
[ 144.967630] [<c1f5e11d>] store+0xa4/0xbd
[ 144.967630] [<c11fa00f>] flush_write_buffer+0x6d/0x81
[ 144.967630] [<c11fb23f>] sysfs_write_file+0x66/0xa6
[ 144.967630] [<c11814e0>] vfs_write+0x1ad/0x1f9
[ 144.967630] [<c1181fc6>] sys_write+0x5e/0x80
[ 144.967630] [<c100582b>] sysenter_do_call+0x12/0x38
[ 144.967630] [<ffffffff>] 0xffffffff
[ 144.967630]
[ 144.967630] other info that might help us debug this:
[ 144.967630]
[ 144.967630] 2 locks held by S99local/8461:
[ 144.967630] #0: (&buffer->mutex){+.+.+.}, at: [<c11fb201>] sysfs_write_file+0x28/0xa6
[ 144.967630] #1: (&per_cpu(cpu_policy_rwsem, cpu)){+++++.}, at: [<c1f5dd3f>] lock_policy_rwsem_write+0x73/0xec
[ 144.967630]
[ 144.967630] stack backtrace:
[ 144.967630] Pid: 8461, comm: S99local Tainted: G W 2.6.30-tip-08973-gb747c8d-dirty #6295
[ 144.967630] Call Trace:
[ 144.967630] [<c10bb9d8>] print_circular_bug_tail+0x5d/0x68
[ 144.967630] [<c10bcc50>] check_prev_add+0x33/0x151
[ 144.967630] [<c10b8974>] ? list_add_tail_rcu+0xd/0xf
[ 144.967630] [<c10bcdd3>] check_prevs_add+0x65/0xbf
[ 144.967630] [<c10bce9e>] validate_chain+0x71/0x99
[ 144.967630] [<c10bd184>] __lock_acquire+0x2be/0x33d
[ 144.967630] [<c10bd27f>] lock_acquire+0x7c/0x9f
[ 144.967630] [<c109962a>] ? wait_on_work+0x0/0xba
[ 144.967630] [<c1099662>] wait_on_work+0x38/0xba
[ 144.967630] [<c109962a>] ? wait_on_work+0x0/0xba
[ 144.967630] [<c110c292>] ? ftrace_likely_update+0x11/0x22
[ 144.967630] [<c109975c>] __cancel_work_timer+0x78/0x99
[ 144.967630] [<c109978d>] cancel_delayed_work_sync+0x10/0x12
[ 144.967630] [<c1f62710>] dbs_timer_exit+0x17/0x19
[ 144.967630] [<c1f62d68>] cpufreq_governor_dbs+0x23f/0x2df
[ 144.967630] [<c1f5e7cb>] __cpufreq_governor+0x9a/0xde
[ 144.967630] [<c1f5ea3c>] __cpufreq_set_policy+0x22d/0x2fa
[ 144.967630] [<c1f5ebce>] store_scaling_governor+0xc5/0x108
[ 144.967630] [<c1f60123>] ? handle_update+0x0/0x2d
[ 144.967630] [<c1f5dd6f>] ? lock_policy_rwsem_write+0xa3/0xec
[ 144.967630] [<c1f5e11d>] store+0xa4/0xbd
[ 144.967630] [<c11fa00f>] flush_write_buffer+0x6d/0x81
[ 144.967630] [<c11fb23f>] sysfs_write_file+0x66/0xa6
[ 144.967630] [<c11814e0>] vfs_write+0x1ad/0x1f9
[ 144.967630] [<c1181fc6>] sys_write+0x5e/0x80
[ 144.967630] [<c100582b>] sysenter_do_call+0x12/0x38
[ 146.085749] PM: Adding info for No Bus:vcs4
[ 146.085864] PM: Adding info for No Bus:vcsa4
[ 146.090924] PM: Adding info for No Bus:vcs9
[ 146.091077] PM: Adding info for No Bus:vcsa9
[ 146.092977] PM: Adding info for No Bus:vcs3


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