FAILED: patch "[PATCH] epoll: Add synchronous wakeup support for ep_poll_callback" failed to apply to 5.4-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 5.4-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 <stable@vger.kernel.org>.

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-5.4.y
git checkout FETCH_HEAD
git cherry-pick -x 900bbaae67e980945dec74d36f8afe0de7556d5a
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2024122326-viscous-dreaded-d15d@gregkh' --subject-prefix 'PATCH 5.4.y' HEAD^..

Possible dependencies:



thanks,

greg k-h

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

From 900bbaae67e980945dec74d36f8afe0de7556d5a Mon Sep 17 00:00:00 2001
From: Xuewen Yan <xuewen.yan@unisoc.com>
Date: Fri, 26 Apr 2024 16:05:48 +0800
Subject: [PATCH] epoll: Add synchronous wakeup support for ep_poll_callback

Now, the epoll only use wake_up() interface to wake up task.
However, sometimes, there are epoll users which want to use
the synchronous wakeup flag to hint the scheduler, such as
Android binder driver.
So add a wake_up_sync() define, and use the wake_up_sync()
when the sync is true in ep_poll_callback().

Co-developed-by: Jing Xia <jing.xia@unisoc.com>
Signed-off-by: Jing Xia <jing.xia@unisoc.com>
Signed-off-by: Xuewen Yan <xuewen.yan@unisoc.com>
Link: https://lore.kernel.org/r/20240426080548.8203-1-xuewen.yan@unisoc.com
Tested-by: Brian Geffon <bgeffon@google.com>
Reviewed-by: Brian Geffon <bgeffon@google.com>
Reported-by: Benoit Lize <lizeb@google.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>

diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 90fbab6b6f03..1a06e462b6ef 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -1373,7 +1373,10 @@ static int ep_poll_callback(wait_queue_entry_t *wait, unsigned mode, int sync, v
 				break;
 			}
 		}
-		wake_up(&ep->wq);
+		if (sync)
+			wake_up_sync(&ep->wq);
+		else
+			wake_up(&ep->wq);
 	}
 	if (waitqueue_active(&ep->poll_wait))
 		pwake++;
diff --git a/include/linux/wait.h b/include/linux/wait.h
index 8aa3372f21a0..2b322a9b88a2 100644
--- a/include/linux/wait.h
+++ b/include/linux/wait.h
@@ -221,6 +221,7 @@ void __wake_up_pollfree(struct wait_queue_head *wq_head);
 #define wake_up_all(x)			__wake_up(x, TASK_NORMAL, 0, NULL)
 #define wake_up_locked(x)		__wake_up_locked((x), TASK_NORMAL, 1)
 #define wake_up_all_locked(x)		__wake_up_locked((x), TASK_NORMAL, 0)
+#define wake_up_sync(x)			__wake_up_sync(x, TASK_NORMAL)
 
 #define wake_up_interruptible(x)	__wake_up(x, TASK_INTERRUPTIBLE, 1, NULL)
 #define wake_up_interruptible_nr(x, nr)	__wake_up(x, TASK_INTERRUPTIBLE, nr, NULL)