On Sat, Sep 21, 2013 at 11:30 AM, Davidlohr Bueso <davidl...@hp.com> wrote:
>
> IPC uses security_xxx_free() at two levels: for freeing the structure
> (ie: shm_destroy()) and cleaning up upon error when creating the
> structure (ie: newseg()). For both I believe we can actually use RCU.
> What do you think of the below change, it is specific for shm, and we'd
> need an equivalent for msq and sems.
Ugh.
This code already has rcu-delaying, usign the existing "rcu" list
entry. I hate how you add a *new* rcu list entry, and we basically
case two callbacks.
More importantly, it's wrong. You do the call_rcu() unconditionally,
but it might not be the last use! You need to do it with the same
logic ipc_rcu_putref(), namely at the dropping of the last reference.
So how about just making ipc_rcu_putref() have a RCU callback
argument, and make the code look something like
ipc_rcu_putref(shp, shm_rcu_free);
and then shm_rcu_free() just does
#define ipc_rcu_to_struct(p) ((void *)(p+1))
void shm_rcu_free(struct rcu_head *head)
{
struct ipc_rcu *p = container_of(head, struct ipc_rcu, rcu);
struct shmid_kernel *shp = ipc_rcu_to_struct(p);
security_shm_free(shp);
ipc_rcu_free(head);
}
(that "ipc_rcu_free()" would do the current vfree-vs-kfree, just not
rcu-delayed, so it would look something like
void ipc_rcu_free(struct rcu_head *head)
{
struct ipc_rcu *p = container_of(head, struct ipc_rcu, rcu);
if (is_vmalloc_addr(p))
vfree(p);
else
kfree(p);
}
Other users would then just use
ipc_rcu_putref(shp, ipc_rcu_free);
until they too decide that they want to do something extra at RCU freeing time..
Hmm?
Linus
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