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>
---
Changes in v2:
* move user and crosstask check before get_callchain_entry
v1:
https://lore.kernel.org/linux-perf-users/CAEf4BzaWtOeTBb_+b7Td3NHaKjZU+OohuBJje_nvw9kd6xPA3g@xxxxxxxxxxxxxx/T/#t
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..104ea2975a57 100644
--- a/kernel/events/callchain.c
+++ b/kernel/events/callchain.c
@@ -184,6 +184,9 @@ get_perf_callchain(struct pt_regs *regs, u32 init_nr, bool kernel, bool user,
struct perf_callchain_entry_ctx ctx;
int rctx;
+ if (user && crosstask)
+ return NULL;
+
entry = get_callchain_entry(&rctx);
if (!entry)
return NULL;
@@ -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
