FROMGIT: rust: sync: condvar: Add wait_interruptible_freezable()

To support waiting for a `CondVar` as a freezable process, add a
wait_interruptible_freezable() function.

Binder needs this function in the appropriate places to freeze a process
where some of its threads are blocked on the Binder driver.

[Boqun: Capitalize the title and reword the commit log]

Signed-off-by: Alice Ryhl <aliceryhl@google.com>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Link: https://lore.kernel.org/r/20250204-condvar-freeze-v2-1-804483096260@google.com

Bug: 388786466
(cherry picked from commit 39dfd06783c0e256f420695ea85d95a5f471bc22
 git://git.kernel.org/pub/scm/linux/kernel/git/boqun/linux.git lockdep-for-tip)
Change-Id: I04c41d20868898a3371ebafa54e4afb76edc762e
Signed-off-by: Alice Ryhl <aliceryhl@google.com>

rust/kernel/sync/condvar.rs

@@ -10,7 +10,9 @@ use crate::{
     init::PinInit,
     pin_init,
     str::CStr,
-    task::{MAX_SCHEDULE_TIMEOUT, TASK_INTERRUPTIBLE, TASK_NORMAL, TASK_UNINTERRUPTIBLE},
+    task::{
+        MAX_SCHEDULE_TIMEOUT, TASK_FREEZABLE, TASK_INTERRUPTIBLE, TASK_NORMAL, TASK_UNINTERRUPTIBLE,
+    },
     time::Jiffies,
     types::Opaque,
 };
@@ -160,6 +162,25 @@ impl CondVar {
         crate::current!().signal_pending()
     }
 
+    /// Releases the lock and waits for a notification in interruptible and freezable mode.
+    ///
+    /// The process is allowed to be frozen during this sleep. You must not hold any locks while
+    /// this operation is ongoing, and there is a lockdep assertion for this. Freezing a task that
+    /// holds a lock can trivially deadlock vs another task that needs that lock to complete before
+    /// it too can hit freezable.
+    #[must_use = "wait returns if a signal is pending, so the caller must check the return value"]
+    pub fn wait_interruptible_freezable<T: ?Sized, B: Backend>(
+        &self,
+        guard: &mut Guard<'_, T, B>,
+    ) -> bool {
+        self.wait_internal(
+            TASK_INTERRUPTIBLE | TASK_FREEZABLE,
+            guard,
+            MAX_SCHEDULE_TIMEOUT,
+        );
+        crate::current!().signal_pending()
+    }
+
     /// Releases the lock and waits for a notification in interruptible mode.
     ///
     /// Atomically releases the given lock (whose ownership is proven by the guard) and puts the