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Date:   Tue, 8 Sep 2020 15:21:28 +0100
From:   Christoph Hellwig <hch@infradead.org>
To:     Ethan Zhao <haifeng.zhao@intel.com>
Cc:     axboe@kernel.dk, bhelgaas@google.com, linux-block@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org,
        mcgrof@kernel.org, ShanshanX.Zhang@intel.com, pei.p.jia@intel.com,
        Ming Lei <ming.lei@redhat.com>
Subject: Re: [PATCH] Revert "block: revert back to synchronous request_queue
 removal"
Message-ID: <20200908142128.GA3463@infradead.org>
References: <20200908075047.5140-1-haifeng.zhao@intel.com>
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On Tue, Sep 08, 2020 at 03:50:48AM -0400, Ethan Zhao wrote:
> From: Ethan Zhao <Haifeng.Zhao@intel.com>
> 
> 'commit e8c7d14ac6c3 ("block: revert back to synchronous request_queue
> removal")' introduced panic issue to NVMe hotplug as following(hit
> after just 2 times NVMe SSD hotplug under stable 5.9-RC2):

I'm pretty sure Ming has already fixed this by not calling put_device
from the rcu callbackm which is the real issue here.

And even if that wasn't the case we generally try to fix bugs instead of
going to a blind revert without much analysis.

> 
> BUG: sleeping function called from invalid context at block/genhd.c:1563
> in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 0, name: swapper/30
> INFO: lockdep is turned off.
> CPU: 30 PID: 0 Comm: swapper/30 Tainted: G S      W         5.9.0-RC2 #3
> Hardware name: Intel Corporation xxxxxxxx
> Call Trace:
> <IRQ>
> dump_stack+0x9d/0xe0
> ___might_sleep.cold.79+0x17f/0x1af
> disk_release+0x26/0x200
> device_release+0x6d/0x1c0
> kobject_put+0x14d/0x430
> hd_struct_free+0xfb/0x260
> percpu_ref_switch_to_atomic_rcu+0x3d1/0x580
> ? rcu_nocb_unlock_irqrestore+0xb6/0xf0
> ? trace_hardirqs_on+0x20/0x1b5
> ? rcu_do_batch+0x3ff/0xb50
> rcu_do_batch+0x47c/0xb50
> ? rcu_accelerate_cbs+0xa9/0x740
> ? rcu_spawn_one_nocb_kthread+0x3d0/0x3d0
> rcu_core+0x945/0xd90
> ? __do_softirq+0x182/0xac0
> __do_softirq+0x1ca/0xac0
> asm_call_on_stack+0xf/0x20
> </IRQ>
> do_softirq_own_stack+0x7f/0x90
> irq_exit_rcu+0x1e3/0x230
> sysvec_apic_timer_interrupt+0x48/0xb0
> asm_sysvec_apic_timer_interrupt+0x12/0x20
> RIP: 0010:cpuidle_enter_state+0x116/0xe90
> Code: 00 31 ff e8 ac c8 a4 fe 80 7c 24 10 00 74 12 9c 58 f6 c4 02
>  0f 85 7e 08 00 00 31 ff e8 43 ca be fe e8 ae a3 d5 fe fb 45 85 ed
>  <0f> 88 4e 05 00 00 4d 63 f5 49 83 fe 09 0f 87 29 0b 00 00 4b 8d 04
> RSP: 0018:ff110001040dfd78 EFLAGS: 00000206
> RAX: 0000000000000007 RBX: ffd1fff7b1a01e00 RCX: 000000000000001f
> RDX: 0000000000000000 RSI: 0000000040000000 RDI: ffffffffb7c5c0f2
> RBP: ffffffffb9a416a0 R08: 0000000000000000 R09: 0000000000000000
> R10: ff110001040d0007 R11: ffe21c002081a000 R12: 0000000000000003
> R13: 0000000000000003 R14: 0000000000000138
> ... ...
> BUG: kernel NULL pointer dereference, address: 0000000000000000
> PGD 0
> Oops: 0010 [#1] SMP KASAN NOPTI
> CPU: 30 PID: 500 Comm: irq/124-pciehp Tainted: G S  W  5.9.0-RC2 #3
> Hardware name: Intel Corporation xxxxxxxx
> RIP: 0010:0x0
> Code: Bad RIP value.
> RSP: 0018:ff110007d5ba75e8 EFLAGS: 00010096
> RAX: 0000000000000000 RBX: ff110001040d0000 RCX: ff110007d5ba7668
> RDX: 0000000000000009 RSI: ff110001040d0000 RDI: ff110008119f59c0
> RBP: ff110008119f59c0 R08: fffffbfff73f7b4d R09: fffffbfff73f7b4d
> R10: ffffffffb9fbda67 R11: fffffbfff73f7b4c R12: 0000000000000000
> R13: ff110007d5ba7668 R14: ff110001040d0000 R15: ff110008119f59c0
> FS:  0000000000000000(0000) GS:ff11000811800000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: ffffffffffffffd6 CR3: 00000007cea16002 CR4: 0000000000771ee0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> PKRU: 55555554
> Call Trace:
> ttwu_do_activate+0xd3/0x160
> try_to_wake_up+0x652/0x1850
> ? migrate_swap_stop+0xad0/0xad0
> ? lock_contended+0xd70/0xd70
> ? rcu_read_unlock+0x50/0x50
> ? rcu_do_batch+0x3ff/0xb50
> swake_up_locked+0x85/0x1c0
> complete+0x4d/0x70
> rcu_do_batch+0x47c/0xb50
> ? rcu_spawn_one_nocb_kthread+0x3d0/0x3d0
> rcu_core+0x945/0xd90
> ? __do_softirq+0x182/0xac0
> __do_softirq+0x1ca/0xac0
> irq_exit_rcu+0x1e3/0x230
> sysvec_apic_timer_interrupt+0x48/0xb0
> asm_sysvec_apic_timer_interrupt+0x12/0x20
> RIP: 0010:_raw_spin_unlock_irqrestore+0x40/0x50
> Code: e8 35 ad 36 fe 48 89 ef e8 cd ce 37 fe f6 c7 02 75 11 53 9d
>  e8 91 1f 5c fe 65 ff 0d ba af c2 47 5b 5d c3 e8 d2 22 5c fe 53 9d
>  <eb> ed 0f 1f 40 00 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 53
> RSP: 0018:ff110007d5ba79d0 EFLAGS: 00000293
> RAX: 0000000000000007 RBX: 0000000000000293 RCX: ffffffffb67710d4
> RDX: 0000000000000000 RSI: 0000000000000004 RDI: ffffffffb83f41ce
> RBP: ffffffffbb77e740 R08: 0000000000000000 R09: 0000000000000000
> R10: ffffffffbb77e743 R11: fffffbfff76efce8 R12: 000000000000198e
> R13: ff11001031d7a0b0 R14: ffffffffbb77e740 R15: ffffffffbb77e788
> ? do_raw_spin_unlock+0x54/0x230
> ? _raw_spin_unlock_irqrestore+0x3e/0x50
> dma_debug_device_change+0x150/0x5e0
> notifier_call_chain+0x90/0x160
> __blocking_notifier_call_chain+0x6d/0xa0
> device_release_driver_internal+0x37d/0x490
> pci_stop_bus_device+0x123/0x190
> pci_stop_and_remove_bus_device+0xe/0x20
> pciehp_unconfigure_device+0x17e/0x330
> ? pciehp_configure_device+0x3e0/0x3e0
> ? trace_hardirqs_on+0x20/0x1b5
> pciehp_disable_slot+0x101/0x360
> ? pme_is_native.cold.2+0x29/0x29
> pciehp_handle_presence_or_link_change+0x1ac/0xee0
> ? pciehp_handle_disable_request+0x110/0x110
> pciehp_ist.cold.11+0x39/0x54
> ? pciehp_set_indicators+0x190/0x190
> ? alloc_desc+0x510/0xa30
> ? irq_set_affinity_notifier+0x380/0x380
> ? pciehp_set_indicators+0x190/0x190
> ? irq_thread+0x137/0x420
> irq_thread_fn+0x86/0x150
> irq_thread+0x21f/0x420
> ? irq_forced_thread_fn+0x170/0x170
> ? irq_thread_check_affinity+0x210/0x210
> ? __kthread_parkme+0x52/0x1a0
> ? lockdep_hardirqs_on_prepare+0x33e/0x4e0
> ? _raw_spin_unlock_irqrestore+0x3e/0x50
> ? trace_hardirqs_on+0x20/0x1b5
> ? wake_threads_waitq+0x40/0x40
> ? __kthread_parkme+0xd1/0x1a0
> ? irq_thread_check_affinity+0x210/0x210
> kthread+0x36a/0x430
> ? kthread_create_worker_on_cpu+0xc0/0xc0
> ret_from_fork+0x1f/0x30
> ... ...
> CR2: 0000000000000000
> ---[ end trace cedc4047ef91d2ec ]---
> 
> Seems scheduling happened within hardware interrupt context, after
> reverted this patch, stable 5.9-RC4 build was tested with more than 20
> times NVMe SSD hotplug, no panic found.
> 
> This reverts commit e8c7d14ac6c37c173ec606907d38802b00302988.
> 
> Tested-by: Shanshan Zhang <ShanshanX.Zhang@intel.com>
> Signed-off-by: Ethan Zhao <Haifeng.Zhao@intel.com>
> ---
>  block/blk-core.c       |  8 --------
>  block/blk-sysfs.c      | 43 +++++++++++++++++++++---------------------
>  block/genhd.c          | 17 -----------------
>  include/linux/blkdev.h |  2 ++
>  4 files changed, 23 insertions(+), 47 deletions(-)
> 
> diff --git a/block/blk-core.c b/block/blk-core.c
> index 10c08ac50697..1b18a0ef5db1 100644
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -325,9 +325,6 @@ EXPORT_SYMBOL_GPL(blk_clear_pm_only);
>   *
>   * Decrements the refcount of the request_queue kobject. When this reaches 0
>   * we'll have blk_release_queue() called.
> - *
> - * Context: Any context, but the last reference must not be dropped from
> - *          atomic context.
>   */
>  void blk_put_queue(struct request_queue *q)
>  {
> @@ -360,14 +357,9 @@ EXPORT_SYMBOL_GPL(blk_set_queue_dying);
>   *
>   * Mark @q DYING, drain all pending requests, mark @q DEAD, destroy and
>   * put it.  All future requests will be failed immediately with -ENODEV.
> - *
> - * Context: can sleep
>   */
>  void blk_cleanup_queue(struct request_queue *q)
>  {
> -	/* cannot be called from atomic context */
> -	might_sleep();
> -
>  	WARN_ON_ONCE(blk_queue_registered(q));
>  
>  	/* mark @q DYING, no new request or merges will be allowed afterwards */
> diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
> index 7dda709f3ccb..eb347cbe0f93 100644
> --- a/block/blk-sysfs.c
> +++ b/block/blk-sysfs.c
> @@ -901,32 +901,22 @@ static void blk_exit_queue(struct request_queue *q)
>  	bdi_put(q->backing_dev_info);
>  }
>  
> +
>  /**
> - * blk_release_queue - releases all allocated resources of the request_queue
> - * @kobj: pointer to a kobject, whose container is a request_queue
> - *
> - * This function releases all allocated resources of the request queue.
> - *
> - * The struct request_queue refcount is incremented with blk_get_queue() and
> - * decremented with blk_put_queue(). Once the refcount reaches 0 this function
> - * is called.
> - *
> - * For drivers that have a request_queue on a gendisk and added with
> - * __device_add_disk() the refcount to request_queue will reach 0 with
> - * the last put_disk() called by the driver. For drivers which don't use
> - * __device_add_disk() this happens with blk_cleanup_queue().
> + * __blk_release_queue - release a request queue
> + * @work: pointer to the release_work member of the request queue to be released
>   *
> - * Drivers exist which depend on the release of the request_queue to be
> - * synchronous, it should not be deferred.
> - *
> - * Context: can sleep
> + * Description:
> + *     This function is called when a block device is being unregistered. The
> + *     process of releasing a request queue starts with blk_cleanup_queue, which
> + *     set the appropriate flags and then calls blk_put_queue, that decrements
> + *     the reference counter of the request queue. Once the reference counter
> + *     of the request queue reaches zero, blk_release_queue is called to release
> + *     all allocated resources of the request queue.
>   */
> -static void blk_release_queue(struct kobject *kobj)
> +static void __blk_release_queue(struct work_struct *work)
>  {
> -	struct request_queue *q =
> -		container_of(kobj, struct request_queue, kobj);
> -
> -	might_sleep();
> +	struct request_queue *q = container_of(work, typeof(*q), release_work);
>  
>  	if (test_bit(QUEUE_FLAG_POLL_STATS, &q->queue_flags))
>  		blk_stat_remove_callback(q, q->poll_cb);
> @@ -958,6 +948,15 @@ static void blk_release_queue(struct kobject *kobj)
>  	call_rcu(&q->rcu_head, blk_free_queue_rcu);
>  }
>  
> +static void blk_release_queue(struct kobject *kobj)
> +{
> +	struct request_queue *q =
> +		container_of(kobj, struct request_queue, kobj);
> +
> +	INIT_WORK(&q->release_work, __blk_release_queue);
> +	schedule_work(&q->release_work);
> +}
> +
>  static const struct sysfs_ops queue_sysfs_ops = {
>  	.show	= queue_attr_show,
>  	.store	= queue_attr_store,
> diff --git a/block/genhd.c b/block/genhd.c
> index 99c64641c314..7e2edf388c8a 100644
> --- a/block/genhd.c
> +++ b/block/genhd.c
> @@ -887,19 +887,12 @@ static void invalidate_partition(struct gendisk *disk, int partno)
>   * The final removal of the struct gendisk happens when its refcount reaches 0
>   * with put_disk(), which should be called after del_gendisk(), if
>   * __device_add_disk() was used.
> - *
> - * Drivers exist which depend on the release of the gendisk to be synchronous,
> - * it should not be deferred.
> - *
> - * Context: can sleep
>   */
>  void del_gendisk(struct gendisk *disk)
>  {
>  	struct disk_part_iter piter;
>  	struct hd_struct *part;
>  
> -	might_sleep();
> -
>  	blk_integrity_del(disk);
>  	disk_del_events(disk);
>  
> @@ -1553,15 +1546,11 @@ int disk_expand_part_tbl(struct gendisk *disk, int partno)
>   * drivers we also call blk_put_queue() for them, and we expect the
>   * request_queue refcount to reach 0 at this point, and so the request_queue
>   * will also be freed prior to the disk.
> - *
> - * Context: can sleep
>   */
>  static void disk_release(struct device *dev)
>  {
>  	struct gendisk *disk = dev_to_disk(dev);
>  
> -	might_sleep();
> -
>  	blk_free_devt(dev->devt);
>  	disk_release_events(disk);
>  	kfree(disk->random);
> @@ -1806,9 +1795,6 @@ EXPORT_SYMBOL(get_disk_and_module);
>   *
>   * This decrements the refcount for the struct gendisk. When this reaches 0
>   * we'll have disk_release() called.
> - *
> - * Context: Any context, but the last reference must not be dropped from
> - *          atomic context.
>   */
>  void put_disk(struct gendisk *disk)
>  {
> @@ -1823,9 +1809,6 @@ EXPORT_SYMBOL(put_disk);
>   *
>   * This is a counterpart of get_disk_and_module() and thus also of
>   * get_gendisk().
> - *
> - * Context: Any context, but the last reference must not be dropped from
> - *          atomic context.
>   */
>  void put_disk_and_module(struct gendisk *disk)
>  {
> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
> index bb5636cc17b9..59fe9de342e0 100644
> --- a/include/linux/blkdev.h
> +++ b/include/linux/blkdev.h
> @@ -583,6 +583,8 @@ struct request_queue {
>  
>  	size_t			cmd_size;
>  
> +	struct work_struct	release_work;
> +
>  #define BLK_MAX_WRITE_HINTS	5
>  	u64			write_hints[BLK_MAX_WRITE_HINTS];
>  };
> -- 
> 2.18.4
> 
---end quoted text---