sock_create() in kernel

Dec 19, 2012 1 Replies

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Hello,

I was looking in to __sock_create() code to get better understanding of the kernel's internal machinery and found that the kernel calls try_module_get() twice; here is a snippet:

static int __sock_create(struct net *net, int family, int type, int protocol, struct socket **res, int kern) { sock = sock_alloc(); ... if (!try_module_get(pf->owner)) goto out_release;

err = pf->create(net, sock, protocol); ...

if (!try_module_get(sock->ops->owner)) goto out_module_busy

... }

Essentially if socket relevant callbacks are in a module, then whenever every socket() from the user space will bump the module's reference count twice. What's the rationale for such behaviour ?

Thanks.

Mark

[...]

Have you considered reading the comments and looking at the surrounding code?

/* * We will call the ->create function, that possibly is in a loadable * module, so we have to bump that loadable module refcnt first. */ if (!try_module_get(pf->owner)) goto out_release;

/* Now protected by module ref count */ rcu_read_unlock();

err = pf->create(net, sock, protocol, kern); if (err < 0) goto out_module_put;

/* * Now to bump the refcnt of the [loadable] module that owns this * socket at sock_release time we decrement its refcnt. */ if (!try_module_get(sock->ops->owner)) goto out_module_busy;

/* * Now that we're done with the ->create function, the [loadable] * module can have its refcnt decremented */ module_put(pf->owner); [net/socket.c]

sock_create() in kernel

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