perf: Have get_perf_callchain() return NULL if crosstask and user are set

get_perf_callchain() doesn't support cross-task unwinding for user space
stacks, have it return NULL if both the crosstask and user arguments are
set.

Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20250820180428.426423415@kernel.org

diff --git a/kernel/events/callchain.c b/kernel/events/callchain.c
index b0f5bd228cd8c36d35f49c09142882064854ce4b..cd0e3fc7ed05af933cee235dda5932a6d18d7dff 100644 (file)
--- a/kernel/events/callchain.c
+++ b/kernel/events/callchain.c
@@ -224,6 +224,10 @@ get_perf_callchain(struct pt_regs *regs, bool kernel, bool user,
        struct perf_callchain_entry_ctx ctx;
        int rctx, start_entry_idx;
 
+       /* crosstask is not supported for user stacks */
+       if (crosstask && user && !kernel)
+               return NULL;
+
        entry = get_callchain_entry(&rctx);
        if (!entry)
                return NULL;
@@ -240,7 +244,7 @@ get_perf_callchain(struct pt_regs *regs, bool kernel, bool user,
                perf_callchain_kernel(&ctx, regs);
        }
 
-       if (user) {
+       if (user && !crosstask) {
                if (!user_mode(regs)) {
                        if  (current->mm)
                                regs = task_pt_regs(current);
@@ -249,9 +253,6 @@ get_perf_callchain(struct pt_regs *regs, bool kernel, bool user,
                }
 
                if (regs) {
-                       if (crosstask)
-                               goto exit_put;
-
                        if (add_mark)
                                perf_callchain_store_context(&ctx, PERF_CONTEXT_USER);
 
@@ -261,7 +262,6 @@ get_perf_callchain(struct pt_regs *regs, bool kernel, bool user,
                }
        }
 
-exit_put:
        put_callchain_entry(rctx);
 
        return entry;