sparse: simple conditional context tracking

This patch enables a very simple form of conditional context tracking,
namely something like

if (spin_trylock(...)) {
	[...]
	spin_unlock(...);
}

Note that
__ret = spin_trylock(...);
if (__ret) {
	[...]
	spin_unlock(...);
}

does /not/ work since that would require tracking the variable and doing
extra checks to ensure the variable isn't globally accessible or similar
which could lead to race conditions.

To declare a trylock, one uses:

int spin_trylock(...) __attribute__((conditional_context(spinlock,0,1,0)))
{...}

Note that doing this currently excludes that function itself from context
checking completely.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>

1 files changed, 161 insertions, 0 deletions

diff --git a/validation/context-dynamic.c b/validation/context-dynamic.c
new file mode 100644
index 0000000..e3bbb98
--- /dev/null
+++ b/validation/context-dynamic.c
@@ -0,0 +1,161 @@
+static void a(void) __attribute__ ((context(A, 0, 1)))
+{
+    __context__(A, 1);
+}
+
+static void r(void) __attribute__ ((context(A, 1, 0)))
+{
+    __context__(A, -1);
+}
+
+extern int condition, condition2;
+
+static int tl(void) __attribute__ ((conditional_context(A, 0, 1, 0)))
+{
+    if (condition) {
+        a();
+        return 1;
+    }
+    return 0;
+}
+
+static int tl2(void) __attribute__ ((conditional_context(A, 0, 0, 1)))
+{
+    if (condition) {
+        a();
+        return 1;
+    }
+    return 0;
+}
+
+static int dummy(void)
+{
+    return condition + condition2;
+}
+
+static int good_trylock1(void)
+{
+    if (tl()) {
+        r();
+    }
+}
+
+static int good_trylock2(void)
+{
+    if (tl()) {
+        r();
+    }
+
+    if (tl()) {
+        r();
+    }
+}
+static int good_trylock3(void)
+{
+    a();
+    if (tl()) {
+        r();
+    }
+    r();
+    if (tl()) {
+        r();
+    }
+}
+
+static int good_trylock4(void)
+{
+    a();
+    if (tl()) {
+        r();
+    }
+    if (tl()) {
+        r();
+    }
+    r();
+}
+
+static void bad_trylock1(void)
+{
+    a();
+    if (dummy()) {
+        r();
+    }
+    r();
+}
+
+static int good_trylock5(void)
+{
+    if (!tl2()) {
+        r();
+    }
+}
+
+static int good_trylock6(void)
+{
+    if (!tl2()) {
+        r();
+    }
+
+    if (!tl2()) {
+        r();
+    }
+}
+static int good_trylock7(void)
+{
+    a();
+    if (!tl2()) {
+        r();
+    }
+    r();
+    if (!tl2()) {
+        r();
+    }
+}
+
+static int good_trylock8(void)
+{
+    a();
+    if (!tl2()) {
+        r();
+    }
+    if (!tl2()) {
+        r();
+    }
+    r();
+}
+
+static void bad_trylock2(void)
+{
+    a();
+    if (!dummy()) {
+        r();
+    }
+    r();
+}
+
+static int good_switch(void)
+{
+    switch (condition) {
+    case 1:
+        a();
+        break;
+    case 2:
+        a();
+        break;
+    case 3:
+        a();
+        break;
+    default:
+        a();
+    }
+    r();
+}
+
+/*
+ * check-name: Check -Wcontext with lock trylocks
+ *
+ * check-error-start
+context-dynamic.c:83:6: warning: context problem in 'bad_trylock1' - function 'r' expected different context
+context-dynamic.c:133:6: warning: context problem in 'bad_trylock2' - function 'r' expected different context
+ * check-error-end
+ */