linux-kernel - Re: [PATCH driver-core-linus] kernfs: kernfs_notify() must be useable from non-sleepable contexts

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Date:	Tue, 1 Jul 2014 13:51:48 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	Tejun Heo <tj@...nel.org>
Cc:	Jens Axboe <axboe@...nel.dk>,
	"Michael S. Tsirkin" <mst@...hat.com>,
	Christoph Hellwig <hch@....de>,
	Josh Boyer <jwboyer@...oraproject.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	virtualization@...ts.linux-foundation.org,
	"Linux-Kernel@...r. Kernel. Org" <linux-kernel@...r.kernel.org>,
	Brian Lane <bcl@...hat.com>,
	John McCutchan <john@...nmccutchan.com>,
	Robert Love <rlove@...ve.org>,
	Eric Paris <eparis@...isplace.org>
Subject: Re: [PATCH driver-core-linus] kernfs: kernfs_notify() must be
 useable from non-sleepable contexts

On Tue, Jul 01, 2014 at 04:41:03PM -0400, Tejun Heo wrote:
> d911d9874801 ("kernfs: make kernfs_notify() trigger inotify events
> too") added fsnotify triggering to kernfs_notify() which requires a
> sleepable context.  There are already existing users of
> kernfs_notify() which invoke it from an atomic context and in general
> it's silly to require a sleepable context for triggering a
> notification.
> 
> The following is an invalid context bug triggerd by md invoking
> sysfs_notify() from IO completion path.
> 
>  BUG: sleeping function called from invalid context at kernel/locking/mutex.c:586
>  in_atomic(): 1, irqs_disabled(): 1, pid: 0, name: swapper/1
>  2 locks held by swapper/1/0:
>   #0:  (&(&vblk->vq_lock)->rlock){-.-...}, at: [<ffffffffa0039042>] virtblk_done+0x42/0xe0 [virtio_blk]
>   #1:  (&(&bitmap->counts.lock)->rlock){-.....}, at: [<ffffffff81633718>] bitmap_endwrite+0x68/0x240
>  irq event stamp: 33518
>  hardirqs last  enabled at (33515): [<ffffffff8102544f>] default_idle+0x1f/0x230
>  hardirqs last disabled at (33516): [<ffffffff818122ed>] common_interrupt+0x6d/0x72
>  softirqs last  enabled at (33518): [<ffffffff810a1272>] _local_bh_enable+0x22/0x50
>  softirqs last disabled at (33517): [<ffffffff810a29e0>] irq_enter+0x60/0x80
>  CPU: 1 PID: 0 Comm: swapper/1 Not tainted 3.16.0-0.rc2.git2.1.fc21.x86_64 #1
>  Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
>   0000000000000000 f90db13964f4ee05 ffff88007d403b80 ffffffff81807b4c
>   0000000000000000 ffff88007d403ba8 ffffffff810d4f14 0000000000000000
>   0000000000441800 ffff880078fa1780 ffff88007d403c38 ffffffff8180caf2
>  Call Trace:
>   <IRQ>  [<ffffffff81807b4c>] dump_stack+0x4d/0x66
>   [<ffffffff810d4f14>] __might_sleep+0x184/0x240
>   [<ffffffff8180caf2>] mutex_lock_nested+0x42/0x440
>   [<ffffffff812d76a0>] kernfs_notify+0x90/0x150
>   [<ffffffff8163377c>] bitmap_endwrite+0xcc/0x240
>   [<ffffffffa00de863>] close_write+0x93/0xb0 [raid1]
>   [<ffffffffa00df029>] r1_bio_write_done+0x29/0x50 [raid1]
>   [<ffffffffa00e0474>] raid1_end_write_request+0xe4/0x260 [raid1]
>   [<ffffffff813acb8b>] bio_endio+0x6b/0xa0
>   [<ffffffff813b46c4>] blk_update_request+0x94/0x420
>   [<ffffffff813bf0ea>] blk_mq_end_io+0x1a/0x70
>   [<ffffffffa00392c2>] virtblk_request_done+0x32/0x80 [virtio_blk]
>   [<ffffffff813c0648>] __blk_mq_complete_request+0x88/0x120
>   [<ffffffff813c070a>] blk_mq_complete_request+0x2a/0x30
>   [<ffffffffa0039066>] virtblk_done+0x66/0xe0 [virtio_blk]
>   [<ffffffffa002535a>] vring_interrupt+0x3a/0xa0 [virtio_ring]
>   [<ffffffff81116177>] handle_irq_event_percpu+0x77/0x340
>   [<ffffffff8111647d>] handle_irq_event+0x3d/0x60
>   [<ffffffff81119436>] handle_edge_irq+0x66/0x130
>   [<ffffffff8101c3e4>] handle_irq+0x84/0x150
>   [<ffffffff818146ad>] do_IRQ+0x4d/0xe0
>   [<ffffffff818122f2>] common_interrupt+0x72/0x72
>   <EOI>  [<ffffffff8105f706>] ? native_safe_halt+0x6/0x10
>   [<ffffffff81025454>] default_idle+0x24/0x230
>   [<ffffffff81025f9f>] arch_cpu_idle+0xf/0x20
>   [<ffffffff810f5adc>] cpu_startup_entry+0x37c/0x7b0
>   [<ffffffff8104df1b>] start_secondary+0x25b/0x300
> 
> This patch fixes it by punting the notification delivery through a
> work item.  This ends up adding an extra pointer to kernfs_elem_attr
> enlarging kernfs_node by a pointer, which is not ideal but not a very
> big deal either.  If this turns out to be an actual issue, we can move
> kernfs_elem_attr->size to kernfs_node->iattr later.
> 
> Signed-off-by: Tejun Heo <tj@...nel.org>
> Reported-by: Josh Boyer <jwboyer@...oraproject.org>
> Cc: "Michael S. Tsirkin" <mst@...hat.com>
> Cc: Jens Axboe <axboe@...nel.dk>
> ---
>  fs/kernfs/file.c       |   69 +++++++++++++++++++++++++++++++++++++++----------
>  include/linux/kernfs.h |    1 
>  2 files changed, 56 insertions(+), 14 deletions(-)

Looks good to me, do you want to take this with your other kernfs
patches for 3.16-final?  Or if you don't have that, I can take it
through my tree, it's your choice, either is fine for me.

If you want it in your tree, feel free to add:
	Acked-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
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