bit_spinlock: Support Clang's context analysis

The annotations for bit_spinlock.h have simply been using "bitlock" as
the token. For Sparse, that was likely sufficient in most cases. But
Clang's context analysis is more precise, and we need to ensure we
can distinguish different bitlocks.

To do so, add a token context, and a macro __bitlock(bitnum, addr)
that is used to construct unique per-bitlock tokens.

Add the appropriate test.

<linux/list_bl.h> is implicitly included through other includes, and
requires 2 annotations to indicate that acquisition (without release)
and release (without prior acquisition) of its bitlock is intended.

Signed-off-by: Marco Elver <elver@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20251219154418.3592607-14-elver@google.com

1 files changed, 26 insertions, 0 deletions

diff --git a/lib/test_context-analysis.c b/lib/test_context-analysis.c
index 53abea0008f2..be0c5d462a48 100644
--- a/lib/test_context-analysis.c
+++ b/lib/test_context-analysis.c
@@ -4,6 +4,7 @@
  * positive errors when compiled with Clang's context analysis.
  */
 
+#include <linux/bit_spinlock.h>
 #include <linux/build_bug.h>
 #include <linux/mutex.h>
 #include <linux/seqlock.h>
@@ -258,3 +259,28 @@ static void __used test_seqlock_scoped(struct test_seqlock_data *d)
 		(void)d->counter;
 	}
 }
+
+struct test_bit_spinlock_data {
+	unsigned long bits;
+	int counter __guarded_by(__bitlock(3, &bits));
+};
+
+static void __used test_bit_spin_lock(struct test_bit_spinlock_data *d)
+{
+	/*
+	 * Note, the analysis seems to have false negatives, because it won't
+	 * precisely recognize the bit of the fake __bitlock() token.
+	 */
+	bit_spin_lock(3, &d->bits);
+	d->counter++;
+	bit_spin_unlock(3, &d->bits);
+
+	bit_spin_lock(3, &d->bits);
+	d->counter++;
+	__bit_spin_unlock(3, &d->bits);
+
+	if (bit_spin_trylock(3, &d->bits)) {
+		d->counter++;
+		bit_spin_unlock(3, &d->bits);
+	}
+}