From: yangerkun yangerkun@huawei.com

hulk inclusion category: bugfix bugzilla: https://gitee.com/openeuler/kernel/issues/I8U3TT

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Thers is a out-of-order access problem which would cause endless sleep when we use pipe with epoll.

The story is following, we assume the ring size is 2, the ring head is 1, the ring tail is 0, task0 is write task, task1 is read task, task2 is write task. Task0 Task1 Task2 epoll_ctl(fd, EPOLL_CTL_ADD, ...) pipe_poll() poll_wait() tail = READ_ONCE(pipe->tail); // Re-order and get tail=0 pipe_read tail++ //tail=1 pipe_write head++ //head=2 head = READ_ONCE(pipe->head); // head = 2 check ring is full by head - tail Task0 get head = 2 and tail = 0, so it mistake that the pipe ring is full, then task0 is not add into ready list. If the ring is not full anymore, task0 would not be woken up forever.

The reason of this problem is that we got inconsistent head/tail value of the pipe ring, so we fix the problem by getting them protected.

Signed-off-by: yangerkun yangerkun@huawei.com Signed-off-by: Baokun Li libaokun1@huawei.com --- fs/pipe.c | 2 ++ 1 file changed, 2 insertions(+)

diff --git a/fs/pipe.c b/fs/pipe.c index 139190165a1c..34752ba942ab 100644 --- a/fs/pipe.c +++ b/fs/pipe.c @@ -672,8 +672,10 @@ pipe_poll(struct file *filp, poll_table *wait) * if something changes and you got it wrong, the poll * table entry will wake you up and fix it. */ + spin_lock_irq(&pipe->rd_wait.lock); head = READ_ONCE(pipe->head); tail = READ_ONCE(pipe->tail); + spin_unlock_irq(&pipe->rd_wait.lock);

mask = 0; if (filp->f_mode & FMODE_READ) {