The trampoline could be corrupted by the blindly
'tr->flags = BPF_TRAMP_F_TAIL_CALL_CTX' in verifier.
1. A fexit attached to a tail_call_reachable prog. 'tr->flags' became
'BPF_TRAMP_F_CALL_ORIG | BPF_TRAMP_F_TAIL_CALL_CTX'. And, the
trampoline would poke the target prog's nop insn using jmp insn instead
of call insn.
2. Another fexit loaded with the same tail_call_reachable prog target.
'tr->flags' became 'BPF_TRAMP_F_TAIL_CALL_CTX'.
3. Close the first fexit link. Due to no BPF_TRAMP_F_CALL_ORIG in
'tr->flags', the trampoline will fail to restore the prog's nop insn
using call insn.
[ 3.410719] WARNING: kernel/bpf/syscall.c:3551 at bpf_tracing_link_release+0x53/0x60, CPU#1: test_progs/98
...
[ 3.428793] bpf_link_free+0x58/0x130
[ 3.429293] bpf_link_release+0x23/0x30
Fix the warning by updating 'tr->flags' with '|=' and lock.
Fixes: 2b5dcb31a1 ("bpf, x64: Fix tailcall infinite loop")
Signed-off-by: Leon Hwang <leon.hwang@linux.dev>
Reviewed-by: Pu Lehui <pulehui@huawei.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Link: https://lore.kernel.org/bpf/20260722151909.69142-2-leon.hwang@linux.dev
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
61aaa8782b