Re: [PATCH v2 bpf-next 1/4] perf: export get/put_chain_entry()

[Peter Zijlstra]

On Thu, Jun 25, 2020 at 05:13:29PM -0700, Song Liu wrote:
> This would be used by bpf stack mapo.

Would it make sense to sanitize the API a little before exposing it?

diff --git a/kernel/events/callchain.c b/kernel/events/callchain.c
index 334d48b16c36..016894b0d2c2 100644
--- a/kernel/events/callchain.c
+++ b/kernel/events/callchain.c
@@ -159,8 +159,10 @@ static struct perf_callchain_entry 
*get_callchain_entry(int *rctx)
                return NULL;
 
        entries = rcu_dereference(callchain_cpus_entries);
-       if (!entries)
+       if (!entries) {
+               put_recursion_context(this_cpu_ptr(callchain_recursion), rctx);
                return NULL;
+       }
 
        cpu = smp_processor_id();
 
@@ -183,12 +185,9 @@ get_perf_callchain(struct pt_regs *regs, u32 init_nr, bool 
kernel, bool user,
        int rctx;
 
        entry = get_callchain_entry(&rctx);
-       if (rctx == -1)
+       if (!entry || rctx == -1)
                return NULL;
 
-       if (!entry)
-               goto exit_put;
-
        ctx.entry     = entry;
        ctx.max_stack = max_stack;
        ctx.nr        = entry->nr = init_nr;