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authorJuergen Gross <jgross@suse.com>2019-10-01 17:03:55 +0200
committerBoris Ostrovsky <boris.ostrovsky@oracle.com>2019-10-02 16:40:11 -0400
commita8fabb38525c51a094607768bac3ba46b3f4a9d5 (patch)
tree2cd7beab8e2e789f2587ae722d28c4d908d50c02
parent09515706857a7d5a2ffb5ce6a44c0bc7859a745b (diff)
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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: James Dingwall <james@dingwall.me.uk> Fixes: fd8aa9095a95c ("xen: optimize xenbus driver for multiple concurrent xenstore accesses") Cc: <stable@vger.kernel.org> # 4.11 Signed-off-by: Juergen Gross <jgross@suse.com> Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com> Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
-rw-r--r--drivers/xen/xenbus/xenbus_dev_frontend.c20
1 files changed, 18 insertions, 2 deletions
diff --git a/drivers/xen/xenbus/xenbus_dev_frontend.c b/drivers/xen/xenbus/xenbus_dev_frontend.c
index 08adc590f631..597af455a522 100644
--- a/drivers/xen/xenbus/xenbus_dev_frontend.c
+++ b/drivers/xen/xenbus/xenbus_dev_frontend.c
@@ -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);