From d4dd9775ec242425576af93daadb80a34083a53c Mon Sep 17 00:00:00 2001 From: Andrii Nakryiko Date: Thu, 29 Aug 2024 10:42:31 -0700 Subject: bpf: wire up sleepable bpf_get_stack() and bpf_get_task_stack() helpers Add sleepable implementations of bpf_get_stack() and bpf_get_task_stack() helpers and allow them to be used from sleepable BPF program (e.g., sleepable uprobes). Note, the stack trace IPs capturing itself is not sleepable (that would need to be a separate project), only build ID fetching is sleepable and thus more reliable, as it will wait for data to be paged in, if necessary. For that we make use of sleepable build_id_parse() implementation. Now that build ID related internals in kernel/bpf/stackmap.c can be used both in sleepable and non-sleepable contexts, we need to add additional rcu_read_lock()/rcu_read_unlock() protection around fetching perf_callchain_entry, but with the refactoring in previous commit it's now pretty straightforward. We make sure to do rcu_read_unlock (in sleepable mode only) right before stack_map_get_build_id_offset() call which can sleep. By that time we don't have any more use of perf_callchain_entry. Note, bpf_get_task_stack() will fail for user mode if task != current. And for kernel mode build ID are irrelevant. So in that sense adding sleepable bpf_get_task_stack() implementation is a no-op. It feel right to wire this up for symmetry and completeness, but I'm open to just dropping it until we support `user && crosstask` condition. Reviewed-by: Eduard Zingerman Signed-off-by: Andrii Nakryiko Link: https://lore.kernel.org/r/20240829174232.3133883-10-andrii@kernel.org Signed-off-by: Alexei Starovoitov --- kernel/trace/bpf_trace.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) (limited to 'kernel/trace/bpf_trace.c') diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c index 98e395f1baae..68b5905c6eb5 100644 --- a/kernel/trace/bpf_trace.c +++ b/kernel/trace/bpf_trace.c @@ -1507,7 +1507,8 @@ bpf_tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog) case BPF_FUNC_jiffies64: return &bpf_jiffies64_proto; case BPF_FUNC_get_task_stack: - return &bpf_get_task_stack_proto; + return prog->sleepable ? &bpf_get_task_stack_sleepable_proto + : &bpf_get_task_stack_proto; case BPF_FUNC_copy_from_user: return &bpf_copy_from_user_proto; case BPF_FUNC_copy_from_user_task: @@ -1563,7 +1564,7 @@ kprobe_prog_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog) case BPF_FUNC_get_stackid: return &bpf_get_stackid_proto; case BPF_FUNC_get_stack: - return &bpf_get_stack_proto; + return prog->sleepable ? &bpf_get_stack_sleepable_proto : &bpf_get_stack_proto; #ifdef CONFIG_BPF_KPROBE_OVERRIDE case BPF_FUNC_override_return: return &bpf_override_return_proto; -- cgit v1.2.3-70-g09d2