Author: hselasky
Date: Tue Jun 25 11:42:53 2019
New Revision: 349367
URL: https://svnweb.freebsd.org/changeset/base/349367
Log:
Fix for deadlock situation in cuse(3)
The final server unref should be done by the server thread to prevent
deadlock in the client cdevpriv destructor, which cannot destroy
itself.
MFC after: 1 week
Sponsored by: Mellanox Technologies
Modified:
head/sys/fs/cuse/cuse.c
Modified: head/sys/fs/cuse/cuse.c
==============================================================================
--- head/sys/fs/cuse/cuse.c Tue Jun 25 11:40:37 2019 (r349366)
+++ head/sys/fs/cuse/cuse.c Tue Jun 25 11:42:53 2019 (r349367)
@@ -699,12 +699,38 @@ cuse_server_unref(struct cuse_server *pcs)
free(pcs, M_CUSE);
}
+static int
+cuse_server_do_close(struct cuse_server *pcs)
+{
+ int retval;
+
+ cuse_lock();
+ cuse_server_is_closing(pcs);
+ /* final client wakeup, if any */
+ cuse_server_wakeup_all_client_locked(pcs);
+
+ knlist_clear(&pcs->selinfo.si_note, 1);
+
+ retval = pcs->refs;
+ cuse_unlock();
+
+ return (retval);
+}
+
static void
cuse_server_free(void *arg)
{
struct cuse_server *pcs = arg;
- /* drop refcount */
+ /*
+ * The final server unref should be done by the server thread
+ * to prevent deadlock in the client cdevpriv destructor,
+ * which cannot destroy itself.
+ */
+ while (cuse_server_do_close(pcs) != 1)
+ pause("W", hz);
+
+ /* drop final refcount */
cuse_server_unref(pcs);
}
@@ -746,21 +772,10 @@ static int
cuse_server_close(struct cdev *dev, int fflag, int devtype, struct thread *td)
{
struct cuse_server *pcs;
- int error;
- error = cuse_server_get(&pcs);
- if (error != 0)
- goto done;
+ if (cuse_server_get(&pcs) == 0)
+ cuse_server_do_close(pcs);
- cuse_lock();
- cuse_server_is_closing(pcs);
- /* final client wakeup, if any */
- cuse_server_wakeup_all_client_locked(pcs);
-
- knlist_clear(&pcs->selinfo.si_note, 1);
- cuse_unlock();
-
-done:
return (0);
}
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