On 10/17/22 11:01 AM, sdf@xxxxxxxxxx wrote:
+static bool bpf_cgroup_storage_trylock(void) +{ + migrate_disable(); + if (unlikely(this_cpu_inc_return(bpf_cgroup_storage_busy) != 1)) { + this_cpu_dec(bpf_cgroup_storage_busy); + migrate_enable(); + return false; + } + return true; +}Task storage has lock/unlock/trylock; inode storage doesn't; why does cgroup need it as well?
This was added in bc235cdb423a2 to avoid deadlock for tracing program which can get a hold to the same task ptr easily with bpf_get_current_task_btf(). I believe there was no known way to hit this problem in inode storage, so inode storage does not use it.
The common tracing use case to get a hold of the cgroup ptr is through task (including bpf_get_current_task_btf()), so it seems to make sense to mimic the trylock here. I have plan to relax it for all non-tracing programs like cgroup-bpf and bpf-lsm.
