[PATCH bpf-next v2] Add notrace to queued_spin_lock_slowpath

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This patch is to prevent deadlocks when multiple bpf
programs are attached to queued_spin_locks functions. This issue is similar
to what is already discussed[1] before with the spin_lock helpers.

The addition of notrace macro to the queued_spin_locks
has been discussed[2] when bpf_spin_locks are introduced.

[1] https://lore.kernel.org/bpf/CAE5sdEigPnoGrzN8WU7Tx-h-iFuMZgW06qp0KHWtpvoXxf1OAQ@xxxxxxxxxxxxxx/#r
[2] https://lore.kernel.org/all/20190117011629.efxp7abj4bpf5yco@ast-mbp/t/#maf05c4d71f935f3123013b7ed410e4f50e9da82c

Fixes: d83525ca62cf ("bpf: introduce bpf_spin_lock")
Signed-off-by: Siddharth Chintamaneni <sidchintamaneni@xxxxxx>
---
 kernel/locking/qspinlock.c                    |  2 +-
 .../bpf/prog_tests/tracing_failure.c          | 24 +++++++++++++++++++
 .../selftests/bpf/progs/tracing_failure.c     |  6 +++++
 3 files changed, 31 insertions(+), 1 deletion(-)

diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c
index ebe6b8ec7cb3..4d46538d8399 100644
--- a/kernel/locking/qspinlock.c
+++ b/kernel/locking/qspinlock.c
@@ -313,7 +313,7 @@ static __always_inline u32  __pv_wait_head_or_lock(struct qspinlock *lock,
  * contended             :    (*,x,y) +--> (*,0,0) ---> (*,0,1) -'  :
  *   queue               :         ^--'                             :
  */
-void __lockfunc queued_spin_lock_slowpath(struct qspinlock *lock, u32 val)
+notrace void __lockfunc queued_spin_lock_slowpath(struct qspinlock *lock, u32 val)
 {
 	struct mcs_spinlock *prev, *next, *node;
 	u32 old, tail;
diff --git a/tools/testing/selftests/bpf/prog_tests/tracing_failure.c b/tools/testing/selftests/bpf/prog_tests/tracing_failure.c
index a222df765bc3..822ee6c559bc 100644
--- a/tools/testing/selftests/bpf/prog_tests/tracing_failure.c
+++ b/tools/testing/selftests/bpf/prog_tests/tracing_failure.c
@@ -28,10 +28,34 @@ static void test_bpf_spin_lock(bool is_spin_lock)
 	tracing_failure__destroy(skel);
 }
 
+static void test_queued_spin_lock(void)
+{
+	struct tracing_failure *skel;
+	int err;
+
+	skel = tracing_failure__open();
+	if (!ASSERT_OK_PTR(skel, "tracing_failure__open"))
+		return;
+
+	bpf_program__set_autoload(skel->progs.test_queued_spin_lock, true);
+
+	err = tracing_failure__load(skel);
+	if (!ASSERT_OK(err, "tracing_failure__load"))
+		goto out;
+
+	err = tracing_failure__attach(skel);
+	ASSERT_ERR(err, "tracing_failure__attach");
+
+out:
+	tracing_failure__destroy(skel);
+}
+
 void test_tracing_failure(void)
 {
 	if (test__start_subtest("bpf_spin_lock"))
 		test_bpf_spin_lock(true);
 	if (test__start_subtest("bpf_spin_unlock"))
 		test_bpf_spin_lock(false);
+	if (test__start_subtest("queued_spin_lock_slowpath"))
+		test_queued_spin_lock();
 }
diff --git a/tools/testing/selftests/bpf/progs/tracing_failure.c b/tools/testing/selftests/bpf/progs/tracing_failure.c
index d41665d2ec8c..2d2e7fc9d4f0 100644
--- a/tools/testing/selftests/bpf/progs/tracing_failure.c
+++ b/tools/testing/selftests/bpf/progs/tracing_failure.c
@@ -18,3 +18,9 @@ int BPF_PROG(test_spin_unlock, struct bpf_spin_lock *lock)
 {
 	return 0;
 }
+
+SEC("?fentry/queued_spin_lock_slowpath")
+int BPF_PROG(test_queued_spin_lock, struct qspinlock *lock, u32 val)
+{
+	return 0;
+}
-- 
2.43.0





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