Messages in this thread Patch in this message | | | From | Libin <> | Subject | [PATCH 07/14] module: Fix invalid wakeup in wait_for_zero_refcount | Date | Thu, 29 Aug 2013 21:57:42 +0800 |
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If thread is preempted before calling set_current_state(TASK_INTERRUPTIBLE), and the other thread set the condition followed with wake_up_process. After that when this thread is re-scheduled, calling set_current_state to set itself as state TASK_INTERRUPTIBLE, if it is preempted again after that and before __set_current_state(TASK_RUNNING), it triggers the invalid wakeup problem. ----------------------- wait_for_zero_refcount() ----------------------- ... for (;;) { pr_debug("Looking at refcount...\n"); set_current_state(TASK_UNINTERRUPTIBLE); if (module_refcount(mod) == 0) break; schedule(); } __set_current_state(TASK_RUNNING); ...
To solve this problem, using preempt_disable() to bound the operaion that setting the task state and the conditions(set by the wake thread) validation. ----------------------- wait_for_zero_refcount() ----------------------- ... preempt_disable(); for (;;) { pr_debug("Looking at refcount...\n"); set_current_state(TASK_UNINTERRUPTIBLE); if (module_refcount(mod) == 0) break; preempt_enable(); schedule(); preempt_disable(); } __set_current_state(TASK_RUNNING); preempt_enable(); ...
Signed-off-by: Libin <huawei.libin@huawei.com> --- kernel/module.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/kernel/module.c b/kernel/module.c index 2069158..22064e9 100644 --- a/kernel/module.c +++ b/kernel/module.c @@ -816,14 +816,18 @@ static void wait_for_zero_refcount(struct module *mod) { /* Since we might sleep for some time, release the mutex first */ mutex_unlock(&module_mutex); + preempt_disable(); for (;;) { pr_debug("Looking at refcount...\n"); set_current_state(TASK_UNINTERRUPTIBLE); if (module_refcount(mod) == 0) break; + preempt_enable(); schedule(); + preempt_disable(); } - current->state = TASK_RUNNING; + __set_current_state(TASK_RUNNING); + preempt_enable(); mutex_lock(&module_mutex); } -- 1.8.2.1
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