Re: [PATCH v8 15/18] perf: Have get_perf_callchain() return NULL if crosstask and user are set
From: Andrii Nakryiko <hidden>
Date: 2025-05-09 21:53:50
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On Fri, May 9, 2025 at 9:52 AM Steven Rostedt [off-list ref] wrote:
quoted hunk ↗ jump to hunk
From: Josh Poimboeuf <jpoimboe@kernel.org> 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> --- kernel/events/callchain.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-)diff --git a/kernel/events/callchain.c b/kernel/events/callchain.c index b0f5bd228cd8..abf258913ab6 100644 --- 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) + return NULL;
I think get_perf_callchain() supports requesting both user and kernel stack traces, and if it's crosstask, you can still get kernel (but not user) stack, if I'm reading the code correctly. So by just returning NULL early you will change this behavior, no?
quoted hunk ↗ jump to hunk
+ entry = get_callchain_entry(&rctx); if (!entry) return NULL;@@ -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; --2.47.2