From: Martin KaFai Lau kafai@fb.com
commit 88d6f130e5632bbf419a2e184ec7adcbe241260b upstream.
It was reported that the max_t, ilog2, and roundup_pow_of_two macros have exponential effects on the number of states in the sparse checker.
This patch breaks them up by calculating the "nbuckets" first so that the "bucket_log" only needs to take ilog2().
In addition, Linus mentioned:
Patch looks good, but I'd like to point out that it's not just sparse.
You can see it with a simple
make net/core/bpf_sk_storage.i grep 'smap->bucket_log = ' net/core/bpf_sk_storage.i | wc
and see the end result:
1 365071 2686974
That's one line (the assignment line) that is 2,686,974 characters in length.
Now, sparse does happen to react particularly badly to that (I didn't look to why, but I suspect it's just that evaluating all the types that don't actually ever end up getting used ends up being much more expensive than it should be), but I bet it's not good for gcc either.
Fixes: 6ac99e8f23d4 ("bpf: Introduce bpf sk local storage") Reported-by: Randy Dunlap rdunlap@infradead.org Reported-by: Luc Van Oostenryck luc.vanoostenryck@gmail.com Suggested-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Martin KaFai Lau kafai@fb.com Signed-off-by: Daniel Borkmann daniel@iogearbox.net Reviewed-by: Luc Van Oostenryck luc.vanoostenryck@gmail.com Link: https://lore.kernel.org/bpf/20200207081810.3918919-1-kafai@fb.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- net/core/bpf_sk_storage.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-)
--- a/net/core/bpf_sk_storage.c +++ b/net/core/bpf_sk_storage.c @@ -643,9 +643,10 @@ static struct bpf_map *bpf_sk_storage_ma return ERR_PTR(-ENOMEM); bpf_map_init_from_attr(&smap->map, attr);
+ nbuckets = roundup_pow_of_two(num_possible_cpus()); /* Use at least 2 buckets, select_bucket() is undefined behavior with 1 bucket */ - smap->bucket_log = max_t(u32, 1, ilog2(roundup_pow_of_two(num_possible_cpus()))); - nbuckets = 1U << smap->bucket_log; + nbuckets = max_t(u32, 2, nbuckets); + smap->bucket_log = ilog2(nbuckets); cost = sizeof(*smap->buckets) * nbuckets + sizeof(*smap);
ret = bpf_map_charge_init(&smap->map.memory, cost);