Re: [PATCH] rumpdisk: Protect device_open/close and r/w with a mutex for threading

[Samuel Thibault]

Damien Zammit, le sam. 26 févr. 2022 06:29:21 +0000, a ecrit:
> @@ -233,22 +246,32 @@ rumpdisk_device_open (mach_port_t reply_port, 
> mach_msg_type_name_t reply_port_ty
>    bd = search_bd (name);

You also need to protect the list, against concurrent addition of
elements.

> @@ -296,6 +323,8 @@ rumpdisk_device_write (void *d, mach_port_t reply_port,
>    if ((bd->mode & D_WRITE) == 0)
>      return D_INVALID_OPERATION;
> 
> +  pthread_mutex_lock (&rumpdisk_rwlock);
> +

Does rump really need to be accessed sequentially? Isn't it thread-safe?

I guess it is thread-safe, in which case you don't need to protect
rump_sys_* calls from each other. All you need is to protect against
a concurrent device_close call. You can use an rwlock for that:
device_write/read take the rwlock in read mode (and check that the
device is still open), and device_close takes it in write mode.

Samuel