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Commit a8fabb38 authored by Juergen Gross's avatar Juergen Gross Committed by Boris Ostrovsky
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xen/xenbus: fix self-deadlock after killing user process



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: default avatarJames Dingwall <james@dingwall.me.uk>
Fixes: fd8aa909

 ("xen: optimize xenbus driver for multiple concurrent xenstore accesses")
Cc: <stable@vger.kernel.org> # 4.11
Signed-off-by: default avatarJuergen Gross <jgross@suse.com>
Reviewed-by: default avatarBoris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: default avatarBoris Ostrovsky <boris.ostrovsky@oracle.com>
parent 09515706
......@@ -55,6 +55,7 @@
#include <linux/string.h>
#include <linux/slab.h>
#include <linux/miscdevice.h>
#include <linux/workqueue.h>
#include <xen/xenbus.h>
#include <xen/xen.h>
......@@ -116,6 +117,8 @@ struct xenbus_file_priv {
wait_queue_head_t read_waitq;
struct kref kref;
struct work_struct wq;
};
/* Read out any raw xenbus messages queued up. */
......@@ -300,14 +303,14 @@ static void watch_fired(struct xenbus_watch *watch,
mutex_unlock(&adap->dev_data->reply_mutex);
}
static void xenbus_file_free(struct kref *kref)
static void xenbus_worker(struct work_struct *wq)
{
struct xenbus_file_priv *u;
struct xenbus_transaction_holder *trans, *tmp;
struct watch_adapter *watch, *tmp_watch;
struct read_buffer *rb, *tmp_rb;
u = container_of(kref, struct xenbus_file_priv, kref);
u = container_of(wq, struct xenbus_file_priv, wq);
/*
* No need for locking here because there are no other users,
......@@ -333,6 +336,18 @@ static void xenbus_file_free(struct kref *kref)
kfree(u);
}
static void xenbus_file_free(struct kref *kref)
{
struct xenbus_file_priv *u;
/*
* We might be called in xenbus_thread().
* Use workqueue to avoid deadlock.
*/
u = container_of(kref, struct xenbus_file_priv, kref);
schedule_work(&u->wq);
}
static struct xenbus_transaction_holder *xenbus_get_transaction(
struct xenbus_file_priv *u, uint32_t tx_id)
{
......@@ -650,6 +665,7 @@ static int xenbus_file_open(struct inode *inode, struct file *filp)
INIT_LIST_HEAD(&u->watches);
INIT_LIST_HEAD(&u->read_buffers);
init_waitqueue_head(&u->read_waitq);
INIT_WORK(&u->wq, xenbus_worker);
mutex_init(&u->reply_mutex);
mutex_init(&u->msgbuffer_mutex);
......
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