[Devel] [PATCH] kernel: call task_work_run() before exit_task_namespaces()

[Andrei Vagin]

From: Andrei Vagin <avagin at virtuozzo.com>

task_work_run() has to be called before exit_task_namespaces(),
because fuse_abort_conn() is called from __fput(). If it will not
be executed, we can hang in request_wait_answer(). We have seen this
situation when a process was the last member of a mount namespace
and the mount namespace has a vstorage fuse mount.

https://jira.sw.ru/browse/PSBM-68266
Signed-off-by: Andrei Vagin <avagin at virtuozzo.com>
---
 include/linux/task_work.h | 9 +++++++--
 kernel/exit.c             | 9 +++++++++
 kernel/task_work.c        | 4 ++--
 3 files changed, 18 insertions(+), 4 deletions(-)

diff --git a/include/linux/task_work.h b/include/linux/task_work.h
index ca5a1cf..b3af76d 100644
--- a/include/linux/task_work.h
+++ b/include/linux/task_work.h
@@ -14,11 +14,16 @@ init_task_work(struct callback_head *twork, task_work_func_t func)
 
 int task_work_add(struct task_struct *task, struct callback_head *twork, bool);
 struct callback_head *task_work_cancel(struct task_struct *, task_work_func_t);
-void task_work_run(void);
+void __task_work_run(bool exiting);
+
+static inline void task_work_run(void)
+{
+	return __task_work_run(false);
+}
 
 static inline void exit_task_work(struct task_struct *task)
 {
-	task_work_run();
+	__task_work_run(true);
 }
 
 #endif	/* _LINUX_TASK_WORK_H */
diff --git a/kernel/exit.c b/kernel/exit.c
index 3c83db2..ea54a73 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -827,6 +827,15 @@ void do_exit(long code)
 	exit_fs(tsk);
 	if (group_dead)
 		disassociate_ctty(1);
+
+	/*
+	 * task_work_run() has to be called before exit_task_namespaces(),
+	 * because fuse_abort_conn() is called from __fput(). If it will not
+	 * be executed, we can hang in request_wait_answer(). We have seen this
+	 * situation when a process was the last member of a mount namespace
+	 * and the mount namespace has a vstorage fuse mount.
+	 */
+	task_work_run();
 	exit_task_namespaces(tsk);
 	exit_task_work(tsk);
 
diff --git a/kernel/task_work.c b/kernel/task_work.c
index 65bd3c9..f0000c4 100644
--- a/kernel/task_work.c
+++ b/kernel/task_work.c
@@ -46,7 +46,7 @@ task_work_cancel(struct task_struct *task, task_work_func_t func)
 	return work;
 }
 
-void task_work_run(void)
+void __task_work_run(bool exiting)
 {
 	struct task_struct *task = current;
 	struct callback_head *work, *head, *next;
@@ -58,7 +58,7 @@ void task_work_run(void)
 		 */
 		do {
 			work = ACCESS_ONCE(task->task_works);
-			head = !work && (task->flags & PF_EXITING) ?
+			head = !work && exiting ?
 				&work_exited : NULL;
 		} while (cmpxchg(&task->task_works, work, head) != work);
 
-- 
1.8.3.1