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Message-ID: <20160921051810.GA396@swordfish>
Date: Wed, 21 Sep 2016 14:18:10 +0900
From: Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To: akpm@...ux-foundation.org, ssantosh@...nel.org
Cc: davem@...emloft.net, giovanni.cabiddu@...el.com,
gregkh@...uxfoundation.org, herbert@...dor.apana.org.au,
isdn@...ux-pingi.de, mingo@...e.hu, pebolle@...cali.nl,
peterz@...radead.org, salvatore.benedetto@...el.com,
tadeusz.struk@...el.com, tglx@...utronix.de,
mm-commits@...r.kernel.org, linux-kernel@...r.kernel.org,
sfr@...b.auug.org.au, linux-next@...r.kernel.org,
sergey.senozhatsky.work@...il.com, sergey.senozhatsky@...il.com
Subject: Re: + softirq-fix-tasklet_kill-and-its-users.patch added to -mm tree
Hello,
On (09/20/16 14:55), akpm@...ux-foundation.org wrote:
> ------------------------------------------------------
> From: Santosh Shilimkar <ssantosh@...nel.org>
> 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/1472089950-2724-1-git-send-email-ssantosh@kernel.org
> Signed-off-by: Santosh Shilimkar <ssantosh@...nel.org>
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Tadeusz Struk <tadeusz.struk@...el.com>
> Cc: Herbert Xu <herbert@...dor.apana.org.au>
> Cc: "David S. Miller" <davem@...emloft.net>
> Cc: Paul Bolle <pebolle@...cali.nl>
> Cc: Giovanni Cabiddu <giovanni.cabiddu@...el.com>
> Cc: Salvatore Benedetto <salvatore.benedetto@...el.com>
> Cc: Karsten Keil <isdn@...ux-pingi.de>
> Cc: "Peter Zijlstra (Intel)" <peterz@...radead.org>
> Cc: Ingo Molnar <mingo@...e.hu>
> Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
> ---
>
> 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 ssantosh@...nel.org are
>
> softirq-fix-tasklet_kill-and-its-users.patch
>
> --
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