Hi!
On 03/03, Sapkal, Swapnil wrote:
>
> >but if you have time, could you check if this patch (with or without the
> >previous debugging patch) makes any difference? Just to be sure.
>
> Sure, I will give this a try.
Forget ;)
[...snip...]
> --- a/fs/pipe.c
> +++ b/fs/pipe.c
> @@ -417,9 +417,19 @@ static inline int is_packetized(struct file *file)
> /* Done while waiting without holding the pipe lock - thus the READ_ONCE() */
> static inline bool pipe_writable(const struct pipe_inode_info *pipe)
> {
> - unsigned int head = READ_ONCE(pipe->head);
> - unsigned int tail = READ_ONCE(pipe->tail);
> unsigned int max_usage = READ_ONCE(pipe->max_usage);
> + unsigned int head, tail;
> +
> + tail = READ_ONCE(pipe->tail);
> + /*
> + * Since the unsigned arithmetic in this lockless preemptible context
> + * relies on the fact that the tail can never be ahead of head, read
> + * the head after the tail to ensure we've not missed any updates to
> + * the head. Reordering the reads can cause wraparounds and give the
> + * illusion that the pipe is full.
> + */
> + smp_rmb();
> + head = READ_ONCE(pipe->head);
> return !pipe_full(head, tail, max_usage) ||
> !READ_ONCE(pipe->readers);
Ooh, thanks!!!
And sorry, can't work today. To be honest, I have some concerns, but probably
I am wrong... I'll return tomorrow.
In any case, finally we have a hint. Thank you both!
(btw, please look at pipe_poll).
Oleg.
