From e7b2c4069252732d52f1de6d1f7c82d99a156659 Mon Sep 17 00:00:00 2001 From: Oleg Nesterov Date: Fri, 14 Jun 2013 21:09:47 +0200 Subject: [PATCH] fput: task_work_add() can fail if the caller has passed exit_task_work() fput() assumes that it can't be called after exit_task_work() but this is not true, for example free_ipc_ns()->shm_destroy() can do this. In this case fput() silently leaks the file. Change it to fallback to delayed_fput_work if task_work_add() fails. The patch looks complicated but it is not, it changes the code from if (PF_KTHREAD) { schedule_work(...); return; } task_work_add(...) to if (!PF_KTHREAD) { if (!task_work_add(...)) return; /* fallback */ } schedule_work(...); As for shm_destroy() in particular, we could make another fix but I think this change makes sense anyway. There could be another similar user, it is not safe to assume that task_work_add() can't fail. Reported-by: Andrey Vagin Signed-off-by: Oleg Nesterov Signed-off-by: Al Viro --- fs/file_table.c | 19 ++++++++++--------- 1 file changed, 10 insertions(+), 9 deletions(-) diff --git a/fs/file_table.c b/fs/file_table.c index cd4d87a82951..485dc0eddd67 100644 --- a/fs/file_table.c +++ b/fs/file_table.c @@ -306,17 +306,18 @@ void fput(struct file *file) { if (atomic_long_dec_and_test(&file->f_count)) { struct task_struct *task = current; + unsigned long flags; + file_sb_list_del(file); - if (unlikely(in_interrupt() || task->flags & PF_KTHREAD)) { - unsigned long flags; - spin_lock_irqsave(&delayed_fput_lock, flags); - list_add(&file->f_u.fu_list, &delayed_fput_list); - schedule_work(&delayed_fput_work); - spin_unlock_irqrestore(&delayed_fput_lock, flags); - return; + if (likely(!in_interrupt() && !(task->flags & PF_KTHREAD))) { + init_task_work(&file->f_u.fu_rcuhead, ____fput); + if (!task_work_add(task, &file->f_u.fu_rcuhead, true)) + return; } - init_task_work(&file->f_u.fu_rcuhead, ____fput); - task_work_add(task, &file->f_u.fu_rcuhead, true); + spin_lock_irqsave(&delayed_fput_lock, flags); + list_add(&file->f_u.fu_list, &delayed_fput_list); + schedule_work(&delayed_fput_work); + spin_unlock_irqrestore(&delayed_fput_lock, flags); } } -- 2.20.1