Re: [PATCH] virtio: console: Unlock vqs while freeing buffers

From	Amit Shah <amit.shah@redhat.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH] virtio: console: Unlock vqs while freeing buffers
Date	2016-10-25 09:20 +0200
Message-ID	<sw4bE-2p1-9@gated-at.bofh.it> (permalink)
References	<sr3pT-666-5@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On (Tue) 11 Oct 2016 [12:05:15], Matt Redfearn wrote:
> Commit c6017e793b93 ("virtio: console: add locks around buffer removal
> in port unplug path") added locking around the freeing of buffers in the
> vq. However, when free_buf() is called with can_sleep = true and rproc
> is enabled, it calls dma_free_coherent() directly, requiring interrupts
> to be enabled. Currently a WARNING is triggered due to the spin locking
> around free_buf, with a call stack like this:
> 
> WARNING: CPU: 3 PID: 121 at ./include/linux/dma-mapping.h:433
> free_buf+0x1a8/0x288
> Call Trace:
> [<8040c538>] show_stack+0x74/0xc0
> [<80757240>] dump_stack+0xd0/0x110
> [<80430d98>] __warn+0xfc/0x130
> [<80430ee0>] warn_slowpath_null+0x2c/0x3c
> [<807e7c6c>] free_buf+0x1a8/0x288
> [<807ea590>] remove_port_data+0x50/0xac
> [<807ea6a0>] unplug_port+0xb4/0x1bc
> [<807ea858>] virtcons_remove+0xb0/0xfc
> [<807b6734>] virtio_dev_remove+0x58/0xc0
> [<807f918c>] __device_release_driver+0xac/0x134
> [<807f924c>] device_release_driver+0x38/0x50
> [<807f7edc>] bus_remove_device+0xfc/0x130
> [<807f4b74>] device_del+0x17c/0x21c
> [<807f4c38>] device_unregister+0x24/0x38
> [<807b6b50>] unregister_virtio_device+0x28/0x44
> 
> Fix this by restructuring the loops to allow the locks to only be taken
> where it is necessary to protect the vqs, and release it while the
> buffer is being freed.
> 
> Fixes: c6017e793b93 ("virtio: console: add locks around buffer removal in port unplug path")
> Cc: stable@vger.kernel.org
> Signed-off-by: Matt Redfearn <matt.redfearn@imgtec.com>

Reviewed-by: Amit Shah <amit.shah@redhat.com>

Michael, can you pick this up?

Thanks,

		Amit

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Re: [PATCH] virtio: console: Unlock vqs while freeing buffers Amit Shah <amit.shah@redhat.com> - 2016-10-25 09:20 +0200
  Re: [PATCH] virtio: console: Unlock vqs while freeing buffers "Michael S. Tsirkin" <mst@redhat.com> - 2016-10-25 15:20 +0200

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