[PATCH v2] coccinelle: locks: Add balancedlock.cocci script

[Sumera Priyadarsini]

When acquiring locks under certain conditions, they must be released
under the same conditions as well. However, sometimes, there may be
missing unlocks which may lead to a potential deadlock.

Add this script to detect such code segments and avoid potential
deadlock situations.

Signed-off-by: Sumera Priyadarsini <sylphrenadin@xxxxxxxxx>
---
Changes in v2(as suggested by Markus):
- Modify usage of position variable
- Modify comments
- Add dependencies for rules
---
 scripts/coccinelle/locks/balancedlock.cocci | 164 ++++++++++++++++++++
 1 file changed, 164 insertions(+)
 create mode 100644 scripts/coccinelle/locks/balancedlock.cocci

diff --git a/scripts/coccinelle/locks/balancedlock.cocci b/scripts/coccinelle/locks/balancedlock.cocci
new file mode 100644
index 000000000000..9684a9920f79
--- /dev/null
+++ b/scripts/coccinelle/locks/balancedlock.cocci
@@ -0,0 +1,164 @@
+/// Sometimes, locks that are acquired under certain conditions may have
+/// missing unlocks leading to a potential deadlock situation. This
+/// semantic patch detects such cases.
+//# False positives may be generated due to locks released within a nested
+//# function call or a goto block.
+///
+// Confidence: Moderate
+// Copyright: (C) 2020 Julia Lawall INRIA/LIP6
+// Copyright: (C) 2020 Sumera Priyadarsini
+
+virtual context
+virtual org
+virtual report
+
+
+@prelocked@
+expression E;
+position p;
+@@
+
+(
+mutex_lock@p(E);
+|
+read_lock@p(E);
+|
+write_lock@p(E);
+|
+spin_lock@p(E);
+|
+spin_lock_bh@p(E);
+|
+spin_lock_irqsave@p(E, ...);
+|
+read_lock_irqsave@p(E, ...);
+|
+write_lock_irqsave@p(E, ...);
+|
+raw_spin_lock@p(E);
+|
+raw_spin_lock_irq@p(E);
+|
+raw_spin_lock_bh@p(E);
+|
+local_lock@p(E);
+|
+local_lock_irq@p(E);
+|
+local_lock_irqsave@p(E, ...);
+|
+read_lock_irq@p(E);
+|
+read_lock_bh@p(E);
+|
+write_lock_bh@p(E);
+)
+
+@balanced@ depends on context || org || report@
+position prelocked.p;
+position pif;
+expression e,prelocked.E;
+statement S1,S2;
+identifier lock;
+identifier unlock={mutex_unlock,
+                   spin_unlock,
+                   spin_unlock_bh,
+                   spin_unlock_irqrestore,
+                   read_unlock_irqrestore,
+                   write_unlock_irqrestore,
+                   raw_spin_unlock,
+                   raw_spin_unlock_irq,
+                   raw_spin_unlock_bh,
+                   local_unlock,
+                   local_unlock_irq,
+                   local_unlock_irqrestore,
+                   read_unlock_irq,
+                   read_unlock_bh,
+                   write_unlock_bh
+                   };
+@@
+
+if (e) {
+ ... when any
+lock@p(E, ...)
+ ... when != E
+     when any
+} else S1
+... when != E
+    when any
+if@pif (e) {
+ ... when != E
+     when any
+ unlock(E, ...);
+ ... when any
+} else S2
+...  when != E
+     when any
+
+// ----------------------------------------------------------------------------
+
+@balanced2 depends on context || org || report@
+identifier lock, unlock = {mutex_unlock,
+                           spin_unlock,
+                           spin_unlock_bh,
+                           spin_unlock_irqrestore,
+                           read_unlock_irqrestore,
+                           write_unlock_irqrestore,
+                           raw_spin_unlock,
+                           raw_spin_unlock_irq,
+                           raw_spin_unlock_bh,
+                           local_unlock,
+                           local_unlock_irq,
+                           local_unlock_irqrestore,
+                           read_unlock_irq,
+                           read_unlock_bh,
+                           write_unlock_bh
+                           };
+expression E, f, x;
+statement S1, S2, S3, S4;
+position prelocked.p, balanced.pif;
+position j0, j1, j2, j3;
+@@
+
+* lock@j0@p(E, ...);
+... when != E;
+    when != if@pif (...) S1 else S2
+    when any
+x@j1 = f(...);
+* if (<+...x...+>)
+{
+  ... when != E;
+      when forall
+      when != if@pif (...) S3 else S4
+*  return@j2 ...;
+}
+... when any
+* unlock@j3(E, ...);
+
+// ----------------------------------------------------------------------------
+
+@script:python balanced2_org depends on org@
+j0 << balanced2.j0;
+j1 << balanced2.j1;
+j2 << balanced2.j2;
+j3 << balanced2.j3;
+@@
+
+msg = "This code segment might have an unbalanced lock."
+coccilib.org.print_todo(j0[0], msg)
+coccilib.org.print_link(j1[0], "")
+coccilib.org.print_link(j2[0], "")
+coccilib.org.print_link(j3[0], "")
+
+// ----------------------------------------------------------------------------
+
+@script:python balanced2_report depends on report@
+j0 << balanced2.j0;
+j1 << balanced2.j1;
+j2 << balanced2.j2;
+j3 << balanced2.j3;
+@@
+
+msg = "This code segment might have an unbalanced lock around lines %s,%s,%s." % (j1[0].line,j2[0].line,j3[0].line)
+coccilib.report.print_report(j0[0], msg)
+
-- 
2.25.1