[PATCH RFC] clk: use spinlock for clk_get_rate
Shawn Guo
shawn.guo at linaro.org
Fri Sep 7 04:03:17 EDT 2012
On Thu, Sep 06, 2012 at 04:12:26PM +0800, Shawn Guo wrote:
> A nested locking issue is seen on imx6q (CA9 Quad) as below when cpufreq
> driver is running. It looks like the issue is caused by a simultaneous
> call to clk_get_rate from two smp_twd threads.
>
Sorry. I was confused by the warning dump. Looking at it more closely,
I found it's a warning of sleeping (using mutex) in atomic context.
The function twd_update_frequency() gets called from an atomic context
while it calls clk_get_rate() where a mutex is held.
gic_handle_irq
handle_IPI
generic_smp_call_function_single_interrupt
twd_update_frequency
clk_get_rate
mutex_lock_nested
I just dug out the following patch from Mike which could be a solution
for this problem. Will post it for review shortly.
HACK: arm: reprogram twd based on clk notifier
Regards,
Shawn
> 1) cpu0_set_target
> cpufreq_notify_transition
> ...
> twd_cpufreq_transition
> twd_update_frequency
> clk_get_rate
>
> 2) do_exit
> kernel_init
> smp_prepare_cpus
> percpu_timer_setup
> twd_timer_setup
> clk_get_rate
>
> The patch "clk: new locking scheme for reentrancy" does not help the
> issue. I'm not sure if this is an issue that should be fixed in
> smp_twd driver or it's an use case which should be supported by clk API.
>
> Looking at clk_get_rate() API, it just reads a cached clock rate and
> should be fast enough to hold a spinlock than mutex. It's a quick
> fix to the issue, but I'm not really sure it's the correct one. That's
> why this is a RFC patch.
>
> root at freescale ~$ BUG: sleeping function called from invalid context at /home/r6
> 5073/repos/mxs/linux-2.6/kernel/mutex.c:269
> in_atomic(): 1, irqs_disabled(): 128, pid: 38, name: kworker/0:1
> 4 locks held by kworker/0:1/38:
> #0: (events){.+.+..}, at: [<80037e98>] process_one_work+0x114/0x478
> #1: ((&(&dbs_info->work)->work)){+.+...}, at: [<80037e98>] process_one_work+0x
> 114/0x478
> #2: (&this_dbs_info->timer_mutex){+.+...}, at: [<802e1bfc>] do_dbs_timer+0x38/
> 0x4ec
> #3: (&nh->srcu){......}, at: [<80043bf0>] __srcu_notifier_call_chain+0x0/0xac
> irq event stamp: 60956
> hardirqs last enabled at (60955): [<804012e8>] __mutex_unlock_slowpath+0xf4/0x1
> 6c
> hardirqs last disabled at (60956): [<800684ec>] smp_call_function_single+0x194/0
> x1ec
> softirqs last enabled at (59634): [<8032cca8>] neigh_periodic_work+0x170/0x1d4
> softirqs last disabled at (59630): [<8040346c>] _raw_write_lock_bh+0x1c/0x6c
> Backtrace:
> [<80011d64>] (dump_backtrace+0x0/0x10c) from [<803fc164>] (dump_stack+0x18/0x1c)
> r6:ffff9fd8 r5:805780c0 r4:bf252000 r3:bf9fd000
> [<803fc14c>] (dump_stack+0x0/0x1c) from [<80047484>] (__might_sleep+0x100/0x11c)
> [<80047384>] (__might_sleep+0x0/0x11c) from [<80400edc>] (mutex_lock_nested+0x2c
> /0x344)
> r6:80013c30 r5:bf252000 r4:805c2a04
> [<80400eb0>] (mutex_lock_nested+0x0/0x344) from [<803089ac>] (clk_get_rate+0x1c/
> 0x58)
> [<80308990>] (clk_get_rate+0x0/0x58) from [<80013c48>] (twd_update_frequency+0x1
> 8/0x50)
> r5:bf252000 r4:805cadf4
> [<80013c30>] (twd_update_frequency+0x0/0x50) from [<800684f4>] (smp_call_functio
> n_single+0x19c/0x1ec)
> r4:60000013 r3:bf9fd000
> [<80068358>] (smp_call_function_single+0x0/0x1ec) from [<80013d48>] (twd_cpufreq
> _transition+0x2c/0x38)
> [<80013d1c>] (twd_cpufreq_transition+0x0/0x38) from [<80043970>] (notifier_call_
> chain+0x4c/0x8c)
> [<80043924>] (notifier_call_chain+0x0/0x8c) from [<80043c68>] (__srcu_notifier_c
> all_chain+0x78/0xac)
> r8:ffffffff r7:80b0ab54 r6:80b0abec r5:00000001 r4:80b0ab0c
> r3:ffffffff
> [<80043bf0>] (__srcu_notifier_call_chain+0x0/0xac) from [<80043cbc>] (srcu_notif
> ier_call_chain+0x20/0x28)
> [<80043c9c>] (srcu_notifier_call_chain+0x0/0x28) from [<802dec88>] (cpufreq_noti
> fy_transition+0xa8/0xdc)
> [<802debe0>] (cpufreq_notify_transition+0x0/0xdc) from [<802e350c>] (cpu0_set_ta
> rget+0x18c/0x2a8)
> r6:00000000 r5:80593664 r4:80593610 r3:00000004
> [<802e3380>] (cpu0_set_target+0x0/0x2a8) from [<802de394>] (__cpufreq_driver_tar
> get+0x70/0x88)
> [<802de324>] (__cpufreq_driver_target+0x0/0x88) from [<802e2090>] (do_dbs_timer+
> 0x4cc/0x4ec)
> r4:805c0d28 r3:bf30de40
> [<802e1bc4>] (do_dbs_timer+0x0/0x4ec) from [<80037f0c>] (process_one_work+0x188/
> 0x478)
> [<80037d84>] (process_one_work+0x0/0x478) from [<800385bc>] (worker_thread+0x184
> /0x388)
> [<80038438>] (worker_thread+0x0/0x388) from [<8003d6e8>] (kthread+0x90/0x9c)
> [<8003d658>] (kthread+0x0/0x9c) from [<80024870>] (do_exit+0x0/0x7ac)
> r6:80024870 r5:8003d658 r4:bf86de90
>
> =================================
> [ INFO: inconsistent lock state ]
> 3.5.0+ #342 Not tainted
> ---------------------------------
> inconsistent {HARDIRQ-ON-W} -> {IN-HARDIRQ-W} usage.
> swapper/1/0 [HC1[1]:SC0[0]:HE0:SE1] takes:
> (prepare_lock){?.+...}, at: [<803089ac>] clk_get_rate+0x1c/0x58
> {HARDIRQ-ON-W} state was registered at:
> [<80060b78>] mark_lock+0x154/0x670
> [<80061950>] __lock_acquire+0x8bc/0x19b4
> [<80062f14>] lock_acquire+0x68/0x7c
> [<80400f28>] mutex_lock_nested+0x78/0x344
> [<803096cc>] clk_prepare+0x20/0x40
> [<803f98a0>] twd_timer_setup+0x48/0x26c
> [<803f9590>] percpu_timer_setup+0x70/0xc8
> [<8053f79c>] smp_prepare_cpus+0x74/0x98
> [<8053b8ec>] kernel_init+0x60/0x1c8
> [<80024870>] do_exit+0x0/0x7ac
> irq event stamp: 399240
> hardirqs last enabled at (399237): [<8000f1f4>] default_idle+0x3c/0x4c
> hardirqs last disabled at (399238): [<8000e114>] __irq_svc+0x34/0x60
> softirqs last enabled at (399240): [<80026d78>] _local_bh_enable+0x14/0x18
> softirqs last disabled at (399239): [<80027370>] irq_enter+0x68/0x78
>
> other info that might help us debug this:
> Possible unsafe locking scenario:
>
> CPU0
> ----
> lock(prepare_lock);
> <Interrupt>
> lock(prepare_lock);
>
> *** DEADLOCK ***
>
> no locks held by swapper/1/0.
>
> stack backtrace:
> Backtrace:
> [<80011d64>] (dump_backtrace+0x0/0x10c) from [<803fc164>] (dump_stack+0x18/0x1c)
> r6:bf8142e0 r5:bf814000 r4:806ac794 r3:bf814000
> [<803fc14c>] (dump_stack+0x0/0x1c) from [<803fd444>] (print_usage_bug+0x250/0x2b
> 8)
> [<803fd1f4>] (print_usage_bug+0x0/0x2b8) from [<80060f90>] (mark_lock+0x56c/0x67
> 0)
> [<80060a24>] (mark_lock+0x0/0x670) from [<80061a20>] (__lock_acquire+0x98c/0x19b
> 4)
> [<80061094>] (__lock_acquire+0x0/0x19b4) from [<80062f14>] (lock_acquire+0x68/0x
> 7c)
> [<80062eac>] (lock_acquire+0x0/0x7c) from [<80400f28>] (mutex_lock_nested+0x78/0
> x344)
> r7:00000000 r6:bf872000 r5:805cc858 r4:805c2a04
> [<80400eb0>] (mutex_lock_nested+0x0/0x344) from [<803089ac>] (clk_get_rate+0x1c/
> 0x58)
> [<80308990>] (clk_get_rate+0x0/0x58) from [<80013c48>] (twd_update_frequency+0x1
> 8/0x50)
> r5:bf253d04 r4:805cadf4
> [<80013c30>] (twd_update_frequency+0x0/0x50) from [<80068e20>] (generic_smp_call
> _function_single_interrupt+0xd4/0x13c)
> r4:bf873ee0 r3:80013c30
> [<80068d4c>] (generic_smp_call_function_single_interrupt+0x0/0x13c) from [<80013
> 34c>] (handle_IPI+0xc0/0x194)
> r8:00000001 r7:00000000 r6:80574e48 r5:bf872000 r4:80593958
> [<8001328c>] (handle_IPI+0x0/0x194) from [<800084e8>] (gic_handle_irq+0x58/0x60)
> r8:00000000 r7:bf873f8c r6:bf873f58 r5:80593070 r4:f4000100
> r3:00000005
> [<80008490>] (gic_handle_irq+0x0/0x60) from [<8000e124>] (__irq_svc+0x44/0x60)
> Exception stack(0xbf873f58 to 0xbf873fa0)
> 3f40: 00000001 00000001
> 3f60: 00000000 bf814000 bf872000 805cab48 80405aa4 80597648 00000000 412fc09a
> 3f80: bf872000 bf873fac bf873f70 bf873fa0 80063844 8000f1f8 20000013 ffffffff
> r6:ffffffff r5:20000013 r4:8000f1f8 r3:bf814000
> [<8000f1b8>] (default_idle+0x0/0x4c) from [<8000f428>] (cpu_idle+0x98/0x114)
> [<8000f390>] (cpu_idle+0x0/0x114) from [<803f9834>] (secondary_start_kernel+0x11
> c/0x140)
> [<803f9718>] (secondary_start_kernel+0x0/0x140) from [<103f9234>] (0x103f9234)
> r6:10c03c7d r5:0000001f r4:4f86806a r3:803f921c
>
> Signed-off-by: Shawn Guo <shawn.guo at linaro.org>
> ---
> drivers/clk/clk.c | 5 +++--
> 1 files changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
> index efdfd00..d6fb25b 100644
> --- a/drivers/clk/clk.c
> +++ b/drivers/clk/clk.c
> @@ -566,11 +566,12 @@ EXPORT_SYMBOL_GPL(clk_enable);
> */
> unsigned long clk_get_rate(struct clk *clk)
> {
> + unsigned long flags;
> unsigned long rate;
>
> - mutex_lock(&prepare_lock);
> + spin_lock_irqsave(&enable_lock, flags);
> rate = __clk_get_rate(clk);
> - mutex_unlock(&prepare_lock);
> + spin_unlock_irqrestore(&enable_lock, flags);
>
> return rate;
> }
> --
> 1.7.5.4
>
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