linux-kernel - Re: [PATCH v3] eventpoll: Fix priority inversion problem

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20250711050217.OMtx7Cz6@linutronix.de>
Date: Fri, 11 Jul 2025 07:02:17 +0200
From: Nam Cao <namcao@...utronix.de>
To: Xi Ruoyao <xry111@...111.site>
Cc: Christian Brauner <brauner@...nel.org>,
	Frederic Weisbecker <frederic@...nel.org>,
	Valentin Schneider <vschneid@...hat.com>,
	Alexander Viro <viro@...iv.linux.org.uk>, Jan Kara <jack@...e.cz>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	John Ogness <john.ogness@...utronix.de>,
	Clark Williams <clrkwllms@...nel.org>,
	Steven Rostedt <rostedt@...dmis.org>, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-rt-devel@...ts.linux.dev,
	linux-rt-users@...r.kernel.org, Joe Damato <jdamato@...tly.com>,
	Martin Karsten <mkarsten@...terloo.ca>,
	Jens Axboe <axboe@...nel.dk>
Subject: Re: [PATCH v3] eventpoll: Fix priority inversion problem

On Thu, Jul 10, 2025 at 05:47:57PM +0800, Xi Ruoyao wrote:
> It didn't work :(.

Argh :(

Another possibility is that you are running into event starvation problem.

Can you give the below patch a try? It is not the real fix, the patch hurts
performance badly. But if starvation is really your problem, it should
ameliorate the situation:

diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 895256cd2786..0dcf8e18de0d 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -1764,6 +1764,8 @@ static int ep_send_events(struct eventpoll *ep,
 		__llist_add(n, &txlist);
 	}
 
+	struct llist_node *shuffle = llist_del_all(&ep->rdllist);
+
 	llist_for_each_entry_safe(epi, tmp, txlist.first, rdllink) {
 		init_llist_node(&epi->rdllink);
 
@@ -1778,6 +1780,13 @@ static int ep_send_events(struct eventpoll *ep,
 		}
 	}
 
+	if (shuffle) {
+		struct llist_node *last = shuffle;
+		while (last->next)
+			last = last->next;
+		llist_add_batch(shuffle, last, &ep->rdllist);
+	}
+
 	__pm_relax(ep->ws);
 	mutex_unlock(&ep->mtx);