Subject: Re: + softirq-fix-tasklet_kill-and-its-users.patch added to -mm tree

From: Sergey Senozhatsky <[email-masked]>
Date: Wed, 21 Sep 2016 14:18:10 +0900

Hello,

On (09/20/16 14:55), [email-masked] wrote:
> ------------------------------------------------------
> From: Santosh Shilimkar <[email-masked]>
> Subject: softirq: fix tasklet_kill() and its users
> 
> Semantically the expectation from the tasklet init/kill API should be as
> below.
> 
> tasklet_init() == Init and Enable scheduling
> tasklet_kill() == Disable scheduling and Destroy
> 
> The tasklet_init() API exibits the above behavior but tasklet_kill() does
> not.  The tasklet handler can still get scheduled and run even after
> tasklet_kill().
> 
> There are 2, 3 places where drivers are working around this issue by
> calling tasklet_disable() which will add a usecount and thereby preventing
> the handlers from being called.
> 
> tasklet_enable/tasklet_disable is a pair API and they are expected to be
> used together.  Usage of tasklet_disable() *just* to work around tasklet
> scheduling after a kill is probably not the correct and intended use of
> the API.  We also happen to see similar issues where in the shutdown path
> the tasklet_handler is getting called even after the tasklet_kill().
> 
> We fix this by ensuring that tasklet_kill() does the right thing and
> thereby ensures that the tasklet handler won't run after tasklet_kil()
> with a very simple change.  The patch fixes the tasklet code and also
> removes a few driver workarounds.

this commit makes ksoftirqd/x to burn CPUs on my system. with a small
addition of WARN_ON_ONCE(atomic_read(&t->count) < 1) to tasklet_action(),
I got

[    0.411895] ------------[ cut here ]------------
[    0.411956] WARNING: CPU: 0 PID: 6 at kernel/softirq.c:502 tasklet_action+0xb4/0x12e
[    0.412018] Modules linked in:
[    0.412111] CPU: 0 PID: 6 Comm: ksoftirqd/0 Not tainted 4.8.0-rc7-mm1-dbg-00278-g7f4fca2-dirty #58
[    0.412273]  ffff8801330efd30 ffffffff811f073c 0000000000000000 0000000000000000
[    0.412484]  ffff8801330efd70 ffffffff8103d23e 000001f6330efd50 ffffffff81849be0
[    0.412696]  ffffffff81849be8 ffffffff8179cbfc 0000000000000000 0000000000000000
[    0.412907] Call Trace:
[    0.412961]  [<ffffffff811f073c>] dump_stack+0x68/0x92
[    0.413020]  [<ffffffff8103d23e>] __warn+0xb8/0xd3
[    0.413079]  [<ffffffff8103d2bf>] warn_slowpath_null+0x18/0x1a
[    0.413138]  [<ffffffff810413d8>] tasklet_action+0xb4/0x12e
[    0.413197]  [<ffffffff8104193a>] __do_softirq+0x103/0x20a
[    0.413256]  [<ffffffff81041a5b>] run_ksoftirqd+0x1a/0x4b
[    0.413316]  [<ffffffff8105a25e>] smpboot_thread_fn+0x20c/0x225
[    0.413376]  [<ffffffff8105a052>] ? sort_range+0x1d/0x1d
[    0.413436]  [<ffffffff810578d1>] kthread+0xf4/0xfc
[    0.413494]  [<ffffffff810577dd>] ? kthread_create_on_node+0x1df/0x1df
[    0.413555]  [<ffffffff81057784>] ? kthread_create_on_node+0x186/0x1df
[    0.413616]  [<ffffffff814c0a47>] ret_from_fork+0x27/0x40
[    0.413735] ---[ end trace d79a87896622b4a4 ]---

	-ss

> Link: http://lkml.kernel.org/r/[email-masked]
> Signed-off-by: Santosh Shilimkar <[email-masked]>
> Cc: Greg Kroah-Hartman <[email-masked]>
> Cc: Thomas Gleixner <[email-masked]>
> Cc: Tadeusz Struk <[email-masked]>
> Cc: Herbert Xu <[email-masked]>
> Cc: "David S. Miller" <[email-masked]>
> Cc: Paul Bolle <[email-masked]>
> Cc: Giovanni Cabiddu <[email-masked]>
> Cc: Salvatore Benedetto <[email-masked]>
> Cc: Karsten Keil <[email-masked]>
> Cc: "Peter Zijlstra (Intel)" <[email-masked]>
> Cc: Ingo Molnar <[email-masked]>
> Signed-off-by: Andrew Morton <[email-masked]>
> ---
> 
>  drivers/crypto/qat/qat_common/adf_isr.c    |    1 -
>  drivers/crypto/qat/qat_common/adf_sriov.c  |    1 -
>  drivers/crypto/qat/qat_common/adf_vf_isr.c |    2 --
>  drivers/isdn/gigaset/interface.c           |    1 -
>  kernel/softirq.c                           |    7 ++++---
>  5 files changed, 4 insertions(+), 8 deletions(-)
> 
> diff -puN drivers/crypto/qat/qat_common/adf_isr.c~softirq-fix-tasklet_kill-and-its-users drivers/crypto/qat/qat_common/adf_isr.c
> --- a/drivers/crypto/qat/qat_common/adf_isr.c~softirq-fix-tasklet_kill-and-its-users
> +++ a/drivers/crypto/qat/qat_common/adf_isr.c
> @@ -296,7 +296,6 @@ static void adf_cleanup_bh(struct adf_ac
>  	int i;
>  
>  	for (i = 0; i < hw_data->num_banks; i++) {
> -		tasklet_disable(&priv_data->banks[i].resp_handler);
>  		tasklet_kill(&priv_data->banks[i].resp_handler);
>  	}
>  }
> diff -puN drivers/crypto/qat/qat_common/adf_sriov.c~softirq-fix-tasklet_kill-and-its-users drivers/crypto/qat/qat_common/adf_sriov.c
> --- a/drivers/crypto/qat/qat_common/adf_sriov.c~softirq-fix-tasklet_kill-and-its-users
> +++ a/drivers/crypto/qat/qat_common/adf_sriov.c
> @@ -204,7 +204,6 @@ void adf_disable_sriov(struct adf_accel_
>  	}
>  
>  	for (i = 0, vf = accel_dev->pf.vf_info; i < totalvfs; i++, vf++) {
> -		tasklet_disable(&vf->vf2pf_bh_tasklet);
>  		tasklet_kill(&vf->vf2pf_bh_tasklet);
>  		mutex_destroy(&vf->pf2vf_lock);
>  	}
> diff -puN drivers/crypto/qat/qat_common/adf_vf_isr.c~softirq-fix-tasklet_kill-and-its-users drivers/crypto/qat/qat_common/adf_vf_isr.c
> --- a/drivers/crypto/qat/qat_common/adf_vf_isr.c~softirq-fix-tasklet_kill-and-its-users
> +++ a/drivers/crypto/qat/qat_common/adf_vf_isr.c
> @@ -191,7 +191,6 @@ static int adf_setup_pf2vf_bh(struct adf
>  
>  static void adf_cleanup_pf2vf_bh(struct adf_accel_dev *accel_dev)
>  {
> -	tasklet_disable(&accel_dev->vf.pf2vf_bh_tasklet);
>  	tasklet_kill(&accel_dev->vf.pf2vf_bh_tasklet);
>  	mutex_destroy(&accel_dev->vf.vf2pf_lock);
>  }
> @@ -268,7 +267,6 @@ static void adf_cleanup_bh(struct adf_ac
>  {
>  	struct adf_etr_data *priv_data = accel_dev->transport;
>  
> -	tasklet_disable(&priv_data->banks[0].resp_handler);
>  	tasklet_kill(&priv_data->banks[0].resp_handler);
>  }
>  
> diff -puN drivers/isdn/gigaset/interface.c~softirq-fix-tasklet_kill-and-its-users drivers/isdn/gigaset/interface.c
> --- a/drivers/isdn/gigaset/interface.c~softirq-fix-tasklet_kill-and-its-users
> +++ a/drivers/isdn/gigaset/interface.c
> @@ -524,7 +524,6 @@ void gigaset_if_free(struct cardstate *c
>  	if (!drv->have_tty)
>  		return;
>  
> -	tasklet_disable(&cs->if_wake_tasklet);
>  	tasklet_kill(&cs->if_wake_tasklet);
>  	cs->tty_dev = NULL;
>  	tty_unregister_device(drv->tty, cs->minor_index);
> diff -puN kernel/softirq.c~softirq-fix-tasklet_kill-and-its-users kernel/softirq.c
> --- a/kernel/softirq.c~softirq-fix-tasklet_kill-and-its-users
> +++ a/kernel/softirq.c
> @@ -498,7 +498,7 @@ static void tasklet_action(struct softir
>  		list = list->next;
>  
>  		if (tasklet_trylock(t)) {
> -			if (!atomic_read(&t->count)) {
> +			if (atomic_read(&t->count) == 1) {
>  				if (!test_and_clear_bit(TASKLET_STATE_SCHED,
>  							&t->state))
>  					BUG();
> @@ -534,7 +534,7 @@ static void tasklet_hi_action(struct sof
>  		list = list->next;
>  
>  		if (tasklet_trylock(t)) {
> -			if (!atomic_read(&t->count)) {
> +			if (atomic_read(&t->count) == 1) {
>  				if (!test_and_clear_bit(TASKLET_STATE_SCHED,
>  							&t->state))
>  					BUG();
> @@ -559,7 +559,7 @@ void tasklet_init(struct tasklet_struct
>  {
>  	t->next = NULL;
>  	t->state = 0;
> -	atomic_set(&t->count, 0);
> +	atomic_set(&t->count, 1);
>  	t->func = func;
>  	t->data = data;
>  }
> @@ -576,6 +576,7 @@ void tasklet_kill(struct tasklet_struct
>  		} while (test_bit(TASKLET_STATE_SCHED, &t->state));
>  	}
>  	tasklet_unlock_wait(t);
> +	atomic_dec(&t->count);
>  	clear_bit(TASKLET_STATE_SCHED, &t->state);
>  }
>  EXPORT_SYMBOL(tasklet_kill);
> _
> 
> Patches currently in -mm which might be from [email-masked] are
> 
> softirq-fix-tasklet_kill-and-its-users.patch
> 
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