FAILED: patch "[PATCH] rtmutex: Drop rt_mutex::wait_lock before scheduling" failed to apply to 4.19-stable tree

The patch below does not apply to the 4.19-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-4.19.y
git checkout FETCH_HEAD
git cherry-pick -x d33d26036a0274b472299d7dcdaa5fb34329f91b
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2024090850-nuclear-radar-ea2b@gregkh' --subject-prefix 'PATCH 4.19.y' HEAD^..

Possible dependencies:

d33d26036a02 ("rtmutex: Drop rt_mutex::wait_lock before scheduling") add461325ec5 ("locking/rtmutex: Extend the rtmutex core to support ww_mutex") 1c143c4b65da ("locking/rtmutex: Provide the spin/rwlock core lock function") e17ba59b7e8e ("locking/rtmutex: Guard regular sleeping locks specific functions") 7980aa397cc0 ("locking/rtmutex: Use rt_mutex_wake_q_head") c014ef69b3ac ("locking/rtmutex: Add wake_state to rt_mutex_waiter") 42254105dfe8 ("locking/rwsem: Add rtmutex based R/W semaphore implementation") ebbdc41e90ff ("locking/rtmutex: Provide rt_mutex_slowlock_locked()") 830e6acc8a1c ("locking/rtmutex: Split out the inner parts of 'struct rtmutex'") 531ae4b06a73 ("locking/rtmutex: Split API from implementation") 785159301bed ("locking/rtmutex: Convert macros to inlines") b41cda037655 ("locking/rtmutex: Set proper wait context for lockdep") 2f064a59a11f ("sched: Change task_struct::state")
d6c23bb3a2ad ("sched: Add get_current_state()")
b03fbd4ff24c ("sched: Introduce task_is_running()")
a9e906b71f96 ("Merge branch 'sched/urgent' into sched/core, to pick up fixes")

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From d33d26036a0274b472299d7dcdaa5fb34329f91b Mon Sep 17 00:00:00 2001
From: Roland Xu <[email protected]>
Date: Thu, 15 Aug 2024 10:58:13 +0800
Subject: [PATCH] rtmutex: Drop rt_mutex::wait_lock before scheduling

rt_mutex_handle_deadlock() is called with rt_mutex::wait_lock held. In the good case it returns with the lock held and in the deadlock case it emits a warning and goes into an endless scheduling loop with the lock held, which triggers the 'scheduling in atomic' warning.

Unlock rt_mutex::wait_lock in the dead lock case before issuing the warning and dropping into the schedule for ever loop.

[ tglx: Moved unlock before the WARN(), removed the pointless comment,
massaged changelog, added Fixes tag ]

index 88d08eeb8bc0..fba1229f1de6 100644
@@ -1644,6 +1644,7 @@ static int __sched rt_mutex_slowlock_block(struct rt_mutex_base *lock,
 }
 
 static void __sched rt_mutex_handle_deadlock(int res, int detect_deadlock,
+					     struct rt_mutex_base *lock,
 					     struct rt_mutex_waiter *w)
 {
 	/*

@@ -1656,10 +1657,10 @@ static void __sched rt_mutex_handle_deadlock(int res, int detect_deadlock,
 	if (build_ww_mutex() && w->ww_ctx)
 		return;
 
-	/*
-	 * Yell loudly and stop the task right here.
-	 */
+	raw_spin_unlock_irq(&lock->wait_lock);
+
 	WARN(1, "rtmutex deadlock detected\n");
+
 	while (1) {
 		set_current_state(TASK_INTERRUPTIBLE);
 		rt_mutex_schedule();

@@ -1713,7 +1714,7 @@ static int __sched __rt_mutex_slowlock(struct rt_mutex_base *lock,
 	} else {
 		__set_current_state(TASK_RUNNING);
 		remove_waiter(lock, waiter);
-		rt_mutex_handle_deadlock(ret, chwalk, waiter);
+		rt_mutex_handle_deadlock(ret, chwalk, lock, waiter);
 	}
 
 	/*

From: Roland Xu <[email protected]>

commit d33d26036a0274b472299d7dcdaa5fb34329f91b upstream.

rt_mutex_handle_deadlock() is called with rt_mutex::wait_lock held. In the good case it returns with the lock held and in the deadlock case it emits a warning and goes into an endless scheduling loop with the lock held, which triggers the 'scheduling in atomic' warning.

Unlock rt_mutex::wait_lock in the dead lock case before issuing the warning and dropping into the schedule for ever loop.

[ tglx: Moved unlock before the WARN(), removed the pointless comment,
massaged changelog, added Fixes tag ]

---
Backport to 5.10.y, 5.4.y, 4.19.y

---
 kernel/locking/rtmutex.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

@@ -1205,6 +1205,7 @@ static int __sched
 }
 
 static void rt_mutex_handle_deadlock(int res, int detect_deadlock,
+				     struct rt_mutex *lock,
 				     struct rt_mutex_waiter *w)
 {
 	/*

@@ -1214,6 +1215,7 @@ static void rt_mutex_handle_deadlock(int
 	if (res != -EDEADLOCK || detect_deadlock)
 		return;
 
+	raw_spin_unlock_irq(&lock->wait_lock);
 	/*
 	 * Yell lowdly and stop the task right here.
 	 */

@@ -1269,7 +1271,7 @@ rt_mutex_slowlock(struct rt_mutex *lock,
 	if (unlikely(ret)) {
 		__set_current_state(TASK_RUNNING);
 		remove_waiter(lock, &waiter);
-		rt_mutex_handle_deadlock(ret, chwalk, &waiter);
+		rt_mutex_handle_deadlock(ret, chwalk, lock, &waiter);
 	}
 
 	/*

Now queued up, thanks!

greg k-h