From: Li Lingfeng <lilingfeng3@huawei.com>
To: Mikulas Patocka <mpatocka@redhat.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
Thomas Gleixner <tglx@linutronix.de>
Cc: <linux-kernel@vger.kernel.org>, <dm-devel@lists.linux.dev>,
Mike Snitzer <msnitzer@redhat.com>,
Ignat Korchagin <ignat@cloudflare.com>,
Damien Le Moal <damien.lemoal@wdc.com>,
Bob Liu <bob.liu@oracle.com>, Hou Tao <houtao1@huawei.com>,
Nathan Huckleberry <nhuck@google.com>,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@elte.hu>, "yukuai (C)" <yukuai3@huawei.com>,
yangerkun <yangerkun@huawei.com>,
"zhangyi (F)" <yi.zhang@huawei.com>, <lilingfeng3@huawei.com>,
Li Lingfeng <lilingfeng@huaweicloud.com>
Subject: Re: [PATCH] softirq: fix memory corruption when freeing tasklet_struct
Date: Tue, 9 Apr 2024 22:15:39 +0800 [thread overview]
Message-ID: <4d331659-badd-749d-fba1-271543631a8a@huawei.com> (raw)
In-Reply-To: <82b964f0-c2c8-a2c6-5b1f-f3145dc2c8e5@redhat.com>
Hi
I tried to reproduce the problem by adding mdelay() in
tasklet_action_common() after t->func() but failed.
Since cc->io_queue is created without WQ_UNBOUND, the work queued to it
will be executed by the CPU which queued the work, which means
bio_endio() will not be called until tasklet_action_common has finished.
Could you please clarify how to reproduce the problem mentioned here?
Thanks
在 2024/1/26 2:29, Mikulas Patocka 写道:
> Hi
>
> There's a problem with the tasklet API - there is no reliable way how to
> free a structure that contains tasklet_struct. The problem is that the
> function tasklet_action_common calls task_unlock(t) after it called the
> callback. If the callback does something that frees tasklet_struct,
> task_unlock(t) would write into free memory.
>
> dm-crypt does this - it schedules a tasklet with tasklet_schedule, it does
> encryption inside the tasklet handler (because it performs better than
> doing the encryption in a workqueue), then it submits a workqueue entry
> and calls bio_endio from the workqueue entry.
>
> However, if the workqueue preempts ksoftirqd, this race condition happens:
>
> ksoftirqd:
> * tasklet_action_common
> * t->func(t->data) (that points to kcryptd_crypt_tasklet)
> * kcryptd_crypt_tasklet
> * kcryptd_crypt
> * kcryptd_crypt_read_convert
> * crypt_dec_pending
> * queue_work(cc->io_queue, &io->work);
> now we switch to the workqueue process:
> * kcryptd_io_bio_endio
> * bio_endio(io->base_bio) (this calls clone_endio)
> * clone_endio
> * free_tio
> * bio_put(clone) - the bio is freed
> now we switch back to ksoftirqd:
> * tasklet_action_common calls task_unlock(t)
> * task_unlock(t) touches memory that was already freed when the bio was freed
>
> dm-verity has a similar problem.
>
> In order to fix this bug, I am proposing to add a new flag
> TASKLET_STATE_ONESHOT. The flag indicates that the tasklet will be
> submitted only once and it prevents tasklet_action_common from touching
> the tasklet after the callback completed.
>
> If you have another idea how to solve this bug, let me know.
>
> Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
> Fixes: 39d42fa96ba1 ("dm crypt: add flags to optionally bypass kcryptd workqueues")
> Fixes: 5721d4e5a9cd ("dm verity: Add optional "try_verify_in_tasklet" feature")
> Cc: stable@vger.kernel.org # v5.9+
>
> ---
> drivers/md/dm-crypt.c | 1 +
> drivers/md/dm-verity-target.c | 1 +
> include/linux/interrupt.h | 9 ++++++++-
> kernel/softirq.c | 22 +++++++++++++++-------
> 4 files changed, 25 insertions(+), 8 deletions(-)
>
> Index: linux-2.6/drivers/md/dm-crypt.c
> ===================================================================
> --- linux-2.6.orig/drivers/md/dm-crypt.c 2024-01-18 19:18:30.000000000 +0100
> +++ linux-2.6/drivers/md/dm-crypt.c 2024-01-25 16:42:17.000000000 +0100
> @@ -2265,6 +2265,7 @@ static void kcryptd_queue_crypt(struct d
> if (in_hardirq() || irqs_disabled()) {
> io->in_tasklet = true;
> tasklet_init(&io->tasklet, kcryptd_crypt_tasklet, (unsigned long)&io->work);
> + tasklet_set_oneshot(&io->tasklet);
> tasklet_schedule(&io->tasklet);
> return;
> }
> Index: linux-2.6/include/linux/interrupt.h
> ===================================================================
> --- linux-2.6.orig/include/linux/interrupt.h 2023-11-13 17:39:50.000000000 +0100
> +++ linux-2.6/include/linux/interrupt.h 2024-01-25 16:41:52.000000000 +0100
> @@ -684,7 +684,9 @@ struct tasklet_struct name = { \
> enum
> {
> TASKLET_STATE_SCHED, /* Tasklet is scheduled for execution */
> - TASKLET_STATE_RUN /* Tasklet is running (SMP only) */
> + TASKLET_STATE_RUN, /* Tasklet is running (SMP only) */
> + TASKLET_STATE_ONESHOT /* Don't unlock the tasklet after the callback
> + to avoid writing to free memory */
> };
>
> #if defined(CONFIG_SMP) || defined(CONFIG_PREEMPT_RT)
> @@ -756,6 +758,11 @@ extern void tasklet_init(struct tasklet_
> extern void tasklet_setup(struct tasklet_struct *t,
> void (*callback)(struct tasklet_struct *));
>
> +static inline void tasklet_set_oneshot(struct tasklet_struct *t)
> +{
> + __set_bit(TASKLET_STATE_ONESHOT, &t->state);
> +}
> +
> /*
> * Autoprobing for irqs:
> *
> Index: linux-2.6/kernel/softirq.c
> ===================================================================
> --- linux-2.6.orig/kernel/softirq.c 2023-10-31 15:31:42.000000000 +0100
> +++ linux-2.6/kernel/softirq.c 2024-01-25 17:10:03.000000000 +0100
> @@ -774,18 +774,26 @@ static void tasklet_action_common(struct
>
> if (tasklet_trylock(t)) {
> if (!atomic_read(&t->count)) {
> + /*
> + * If oneshot is set, we must not touch the
> + * tasklet after the callback.
> + */
> + bool oneshot = test_bit(TASKLET_STATE_ONESHOT, &t->state);
> if (tasklet_clear_sched(t)) {
> if (t->use_callback) {
> - trace_tasklet_entry(t, t->callback);
> - t->callback(t);
> - trace_tasklet_exit(t, t->callback);
> + void (*callback)(struct tasklet_struct *) = t->callback;
> + trace_tasklet_entry(t, callback);
> + callback(t);
> + trace_tasklet_exit(t, callback);
> } else {
> - trace_tasklet_entry(t, t->func);
> - t->func(t->data);
> - trace_tasklet_exit(t, t->func);
> + void (*func)(unsigned long) = t->func;
> + trace_tasklet_entry(t, func);
> + func(t->data);
> + trace_tasklet_exit(t, func);
> }
> }
> - tasklet_unlock(t);
> + if (!oneshot)
> + tasklet_unlock(t);
> continue;
> }
> tasklet_unlock(t);
> Index: linux-2.6/drivers/md/dm-verity-target.c
> ===================================================================
> --- linux-2.6.orig/drivers/md/dm-verity-target.c 2024-01-18 19:18:30.000000000 +0100
> +++ linux-2.6/drivers/md/dm-verity-target.c 2024-01-25 18:12:09.000000000 +0100
> @@ -676,6 +676,7 @@ static void verity_end_io(struct bio *bi
>
> if (static_branch_unlikely(&use_tasklet_enabled) && io->v->use_tasklet) {
> tasklet_init(&io->tasklet, verity_tasklet, (unsigned long)io);
> + tasklet_set_oneshot(&io->tasklet);
> tasklet_schedule(&io->tasklet);
> } else {
> INIT_WORK(&io->work, verity_work);
>
prev parent reply other threads:[~2024-04-09 14:15 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-01-25 18:29 [PATCH] softirq: fix memory corruption when freeing tasklet_struct Mikulas Patocka
2024-01-25 19:51 ` Linus Torvalds
2024-01-25 22:04 ` Mikulas Patocka
2024-01-25 23:15 ` Damien Le Moal
2024-01-26 6:56 ` Hannes Reinecke
2024-01-26 18:09 ` Mikulas Patocka
2024-01-29 8:26 ` request based dm-multipath, was " Christoph Hellwig
2024-01-25 22:51 ` Ignat Korchagin
2024-01-26 0:33 ` Tejun Heo
2024-01-26 18:36 ` Allen
2024-01-26 23:43 ` Tejun Heo
2024-01-27 3:13 ` Allen
2024-01-27 18:37 ` Tejun Heo
2024-01-30 9:19 ` Tejun Heo
2024-01-29 17:00 ` Allen
2024-01-29 17:06 ` Tejun Heo
2024-04-09 14:15 ` Li Lingfeng [this message]
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