On Wed, 31 Jul 2019 15:10:55 -0700, Takshak Chahande wrote:

Having static variable `cpus` in libbpf_num_possible_cpus function
without guarding it with mutex makes this function thread-unsafe.

If multiple threads accessing this function, in the current form; it
leads to incrementing the static variable value `cpus` in the multiple
of total available CPUs.

Used local stack variable to calculate the number of possible CPUs and
then updated the static variable using WRITE_ONCE().

Changes since v1:
 * added stack variable to calculate cpus
 * serialized static variable update using WRITE_ONCE()
 * fixed Fixes tag

Fixes: 6446b3155521 ("bpf: add a new API libbpf_num_possible_cpus()")
Signed-off-by: Takshak Chahande <redacted>

Perhaps we would have a little less code churn if the static variable
was renamed (e.g. to saved_cpus), but functionally looks good, so:

Reviewed-by: Jakub Kicinski <redacted>

(FWIW I think Andrey's comment does not apply to the networking and BPF
trees so if you respin please keep the changelog in the commit message.)