Messages in this thread | | | Date | Thu, 17 Nov 2016 09:53:42 +0100 | From | Peter Zijlstra <> | Subject | Re: [RFC][PATCH 2/7] kref: Add kref_read() |
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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.GH3142@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.
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