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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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