On Wed, Nov 16, 2016 at 12:08:52PM -0800, Alexei Starovoitov wrote: > I prefer to avoid 'fixing' things that are not broken. > Note, prog->aux->refcnt already has explicit checks for overflow. > locked_vm is used for resource accounting and not refcnt, > so I don't see issues there either.
The idea is to use something along the lines of: http://lkml.kernel.org/r/20161115104608.gh3...@twins.programming.kicks-ass.net for all refcounts in the kernel. Also note that your: struct bpf_prog *bpf_prog_add(struct bpf_prog *prog, int i) { if (atomic_add_return(i, &prog->aux->refcnt) > BPF_MAX_REFCNT) { atomic_sub(i, &prog->aux->refcnt); return ERR_PTR(-EBUSY); } return prog; } is actually broken in the face of an actual overflow. Suppose @i is big enough to wrap refcnt into negative space. Also, the current sentiment is to strongly discourage add/sub operations for refcounts.
