linux-kernel - Re: [PATCH] xen/xenbus: fix self-deadlock after killing user process

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Date:   Tue, 1 Oct 2019 13:37:24 -0400
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     Juergen Gross <jgross@...e.com>, xen-devel@...ts.xenproject.org,
        linux-kernel@...r.kernel.org
Cc:     Stefano Stabellini <sstabellini@...nel.org>,
        James Dingwall <james@...gwall.me.uk>, stable@...r.kernel.org
Subject: Re: [PATCH] xen/xenbus: fix self-deadlock after killing user process

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@...gwall.me.uk>
> Fixes: fd8aa9095a95c ("xen: optimize xenbus driver for multiple concurrent xenstore accesses")
> Cc: <stable@...r.kernel.org> # 4.11
> Signed-off-by: Juergen Gross <jgross@...e.com>

Reviewed-by: Boris Ostrovsky <boris.ostrovsky@...cle.com>