The patchset fixes a tailcall hierarchy issue.
The issue is confirmed in the discussions of "bpf, x64: Fix tailcall infinite
loop"[0].
But, the issue is only resolved on x86.
Hopefully, the issue on aarch64 and s390x will be resolved soon.
This CI history[1] confirms the issue on aarch64 and s390x.
I provide a long commit message in the first patch to describe how the issue
happens and how this patchset resolves the issue in details.
In short, it uses PERCPU tail_call_cnt to store the temporary tail_call_cnt.
First, at the prologue of bpf prog, it initialise the PERCPU
tail_call_cnt by setting current CPU's tail_call_cnt to 0.
Then, when a tailcall happens, it fetches and increments current CPU's
tail_call_cnt, and compares to MAX_TAIL_CALL_CNT.
v1 -> v2:
* Solution changes from extra run-time call insn to percpu tail_call_cnt.
* Address comments from Alexei:
* Use percpu tail_call_cnt.
* Use asm to make sure no callee saved registers are touched.
RFC v2 -> v1:
* Solution changes from propagating tail_call_cnt with its pointer to extra
run-time call insn.
* Address comments from Maciej:
* Replace all memcpy(prog, x86_nops[5], X86_PATCH_SIZE) with
emit_nops(&prog, X86_PATCH_SIZE)
RFC v1 -> RFC v2:
* Address comments from Stanislav:
* Separate moving emit_nops() as first patch.
Links:
[0] https://lore.kernel.org/bpf/6203dd01-789d-f02c-5293-def4c1b18aef@xxxxxxxxx/
[1] https://github.com/kernel-patches/bpf/pull/6476/checks
Leon Hwang (2):
bpf, x64: Fix tailcall hierarchy
selftests/bpf: Add testcases for tailcall hierarchy fixing
arch/x86/net/bpf_jit_comp.c | 128 +++---
.../selftests/bpf/prog_tests/tailcalls.c | 418 ++++++++++++++++++
.../bpf/progs/tailcall_bpf2bpf_hierarchy1.c | 34 ++
.../bpf/progs/tailcall_bpf2bpf_hierarchy2.c | 55 +++
.../bpf/progs/tailcall_bpf2bpf_hierarchy3.c | 46 ++
5 files changed, 624 insertions(+), 57 deletions(-)
create mode 100644 tools/testing/selftests/bpf/progs/tailcall_bpf2bpf_hierarchy1.c
create mode 100644 tools/testing/selftests/bpf/progs/tailcall_bpf2bpf_hierarchy2.c
create mode 100644 tools/testing/selftests/bpf/progs/tailcall_bpf2bpf_hierarchy3.c
base-commit: 499e99ea0e8020bfc84b2327d4c37e45dc40bbd1
--
2.42.1
