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Re: [Xen-devel] [PATCH] xen/xenbus: fix self-deadlock after killing user process
- To: Juergen Gross <jgross@xxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx
- From: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
- Date: Tue, 1 Oct 2019 13:37:24 -0400
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- Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>, stable@xxxxxxxxxxxxxxx, James Dingwall <james@xxxxxxxxxxxxxx>
- Delivery-date: Tue, 01 Oct 2019 17:37:55 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
- Openpgp: preference=signencrypt
On 10/1/19 11:03 AM, Juergen Gross wrote:
> In case a user process using xenbus has open transactions and is killed
> e.g. via ctrl-C the following cleanup of the allocated resources might
> result in a deadlock due to trying to end a transaction in the xenbus
> worker thread:
>
> [ 2551.474706] INFO: task xenbus:37 blocked for more than 120 seconds.
> [ 2551.492215] Tainted: P OE 5.0.0-29-generic #5
> [ 2551.510263] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables
> this message.
> [ 2551.528585] xenbus D 0 37 2 0x80000080
> [ 2551.528590] Call Trace:
> [ 2551.528603] __schedule+0x2c0/0x870
> [ 2551.528606] ? _cond_resched+0x19/0x40
> [ 2551.528632] schedule+0x2c/0x70
> [ 2551.528637] xs_talkv+0x1ec/0x2b0
> [ 2551.528642] ? wait_woken+0x80/0x80
> [ 2551.528645] xs_single+0x53/0x80
> [ 2551.528648] xenbus_transaction_end+0x3b/0x70
> [ 2551.528651] xenbus_file_free+0x5a/0x160
> [ 2551.528654] xenbus_dev_queue_reply+0xc4/0x220
> [ 2551.528657] xenbus_thread+0x7de/0x880
> [ 2551.528660] ? wait_woken+0x80/0x80
> [ 2551.528665] kthread+0x121/0x140
> [ 2551.528667] ? xb_read+0x1d0/0x1d0
> [ 2551.528670] ? kthread_park+0x90/0x90
> [ 2551.528673] ret_from_fork+0x35/0x40
>
> Fix this by doing the cleanup via a workqueue instead.
>
> Reported-by: James Dingwall <james@xxxxxxxxxxxxxx>
> Fixes: fd8aa9095a95c ("xen: optimize xenbus driver for multiple concurrent
> xenstore accesses")
> Cc: <stable@xxxxxxxxxxxxxxx> # 4.11
> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
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