When debugging use-after-free(UAF) bugs, knowing when the object reaches
0 references and enters final release can significantly aid the
debugging process.
There is currently no universal way to trace this information.
This patch series implements tracing of the final puts in the
most widely used refcounting implementations,
refcount_t(and thus kref which uses it), and percpu-ref.
The tracepoint records three fields:
- caller: function that called the refcounting
function(refcount_sub_and_test, percpu_ref_put_many)
- fn: refcounting function(eg refcount_sub_and_test)
- obj: refcount object(struct percpu_ref, refcount_t)
Signed-off-by: Eugene Mavick <m@mavick.dev>
---
Changes in v2:
-include/linux/ref_trace.h: change macro name, use direct tracepoint
call in macro to avoid double check
-add tracepoint to refcount_dec_if_one
-kunit: make significant improvements to design, fix critical bug, add test case for
refcount_dec_if_one()
-Link to v1: https://lore.kernel.org/r/20260705-refcount-final-put-trace-v1-0-0ae936edb750@mavick.dev
Changes in v3:
include/trace/events/ref_trace.h kernel doc comments:
-caller of refcount function -> return address of refcount function
-ref_trace_final_put->do_ref_trace_final_put
lib/ref_trace.c: add include trace/events/ref_trace.h
kunit:
-change Kconfig depends from FTRACE->TRACEPOINTS
-EXPECT_FALSE->ASSERT_FALSE for calling percpu_ref_init
-add tracepoint_synchronise_unregister to test_exit macro
-added timeout to capture.count waiting
-remove noinline and __always_inline from function attributes
(added for testing, but accidentally submitted)
-add period to the end of Kconfig help text
v2 link:
https://lore.kernel.org/all/20260710-refcount-final-put-trace-v2-0-557cfce860a2@mavick.dev/
---
Eugene Mavick (5):
tracing: add ref_trace_final_put tracepoint
refcount: add ref_trace_final_put tracepoint
percpu-refcount: add ref_trace_final_put trace
kunit: add test for ref_trace_final_put
MAINTAINERS: add entries for ref_trace_final_put
MAINTAINERS | 3 +
include/linux/percpu-refcount.h | 5 +-
include/linux/ref_trace.h | 26 ++++++++
include/linux/refcount.h | 2 +
include/trace/events/ref_trace.h | 46 +++++++++++++
lib/Kconfig | 10 +++
lib/Makefile | 2 +
lib/ref_trace.c | 13 ++++
lib/refcount.c | 8 ++-
lib/tests/Makefile | 1 +
lib/tests/ref_trace_kunit.c | 141 +++++++++++++++++++++++++++++++++++++++
11 files changed, 255 insertions(+), 2 deletions(-)
---
base-commit: df685633c3dbc67441cc86f1c3fee58de4652ba2
change-id: 20260624-refcount-final-put-trace-49bd7c39bd5a
Best regards,
--
Eugene Mavick <m@mavick.dev>