On Tue, 2011-11-08 at 13:45 -0800, Miche Baker-Harvey wrote:
> hvc_init() must only be called once, and no thread should continue with hvc_alloc()
> until after initialization is complete. The original code does not enforce either
> of these requirements. A new mutex limits entry to hvc_init() to a single thread,
> and blocks all later comers until it has completed.
>
> This patch fixes multiple crash symptoms.
Hi Miche,
A few nit-picky comments below ..
> @@ -84,6 +85,10 @@ static LIST_HEAD(hvc_structs);
> * list traversal.
> */
> static DEFINE_SPINLOCK(hvc_structs_lock);
> +/*
> + * only one task does allocation at a time.
> + */
> +static DEFINE_MUTEX(hvc_ports_mutex);
The comment is wrong, isn't it? Only one task does _init_ at a time.
Once the driver is initialised allocs can run concurrently.
So shouldn't it be called hvc_init_mutex ?
> @@ -825,11 +830,15 @@ struct hvc_struct *hvc_alloc(uint32_t vtermno, int data,
> int i;
>
> /* We wait until a driver actually comes along */
> + mutex_lock(&hvc_ports_mutex);
> if (!hvc_driver) {
> int err = hvc_init();
> - if (err)
> + if (err) {
> + mutex_unlock(&hvc_ports_mutex);
> return ERR_PTR(err);
> + }
> }
> + mutex_unlock(&hvc_ports_mutex);
>
> hp = kzalloc(ALIGN(sizeof(*hp), sizeof(long)) + outbuf_size,
> GFP_KERNEL);
It'd be cleaner I think to do all the locking in hvc_init(). That's safe
as long as you recheck !hvc_driver in hvc_init() with the lock held.
cheers
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