On 05/08, Alexei Starovoitov wrote: > On Wed, May 08, 2019 at 10:18:41AM -0700, Stanislav Fomichev wrote: > > Right now we are not using rcu api correctly: we pass __rcu pointers > > to bpf_prog_array_xyz routines but don't use rcu_dereference on them > > (see bpf_prog_array_delete_safe and bpf_prog_array_copy in particular). > > Instead of sprinkling rcu_dereferences, let's just get rid of those > > __rcu annotations and move rcu handling to a higher level. > > > > It looks like all those routines are called from the rcu update > > side and we can use simple rcu_dereference_protected to get a > > reference that is valid as long as we hold a mutex (i.e. no other > > updater can change the pointer, no need for rcu read section and > > there should not be a use-after-free problem). > > > > To be fair, there is currently no issue with the existing approach > > since the calls are mutex-protected, pointer values don't change, > > __rcu annotations are ignored. But it's still nice to use proper api. > > > > The series fixes the following sparse warnings: > > Absolutely not. > please fix it properly. > Removing annotations is not a fix. I'm fixing it properly by removing the annotations and moving lifetime management to the upper layer. See commits 2-4 where I fix the users, the first patch is just the "preparation". The users are supposed to do: mutex_lock(&x); p = rcu_dereference_protected(prog_array, lockdep_is_held(&x)) // ... // call bpf_prog_array helpers while mutex guarantees that // the object referenced by p is valid (i.e. no need for bpf_prog_array // helpers to care about rcu lifetime) // ... mutex_unlock(&x); What am I missing here?
