Return NULL instead of returning 1 incorrect frame, which currently happens when trying to walk the user stack for any task that isn't current. Returning NULL is a better indicator that this behavior is not supported. This issue was found using bpf_get_task_stack inside a BPF iterator ("iter/task"), which iterates over all tasks. The single address/frame in the buffer when getting user stacks for tasks that aren't current could not be symbolized (testing multiple symbolizers). Signed-off-by: Jordan Rome <linux@xxxxxxxxxxxxxx> --- kernel/events/callchain.c | 7 +++---- 1 file changed, 3 insertions(+), 4 deletions(-) diff --git a/kernel/events/callchain.c b/kernel/events/callchain.c index 1273be84392c..430fa544fa80 100644 --- a/kernel/events/callchain.c +++ b/kernel/events/callchain.c @@ -201,6 +201,9 @@ get_perf_callchain(struct pt_regs *regs, u32 init_nr, bool kernel, bool user, } if (user) { + if (crosstask) + return NULL; + if (!user_mode(regs)) { if (current->mm) regs = task_pt_regs(current); @@ -209,9 +212,6 @@ get_perf_callchain(struct pt_regs *regs, u32 init_nr, bool kernel, bool user, } if (regs) { - if (crosstask) - goto exit_put; - if (add_mark) perf_callchain_store_context(&ctx, PERF_CONTEXT_USER); @@ -219,7 +219,6 @@ get_perf_callchain(struct pt_regs *regs, u32 init_nr, bool kernel, bool user, } } -exit_put: put_callchain_entry(rctx); return entry; -- 2.39.3