+ epoll-use-refcount-to-reduce-ep_mutex-contention-v5.patch added to mm-nonmm-unstable branch

+ epoll-use-refcount-to-reduce-ep_mutex-contention-v5.patch added to mm-nonmm-unstable branch

[Andrew Morton]

The patch titled
     Subject: epoll-use-refcount-to-reduce-ep_mutex-contention-v5
has been added to the -mm mm-nonmm-unstable branch.  Its filename is
     epoll-use-refcount-to-reduce-ep_mutex-contention-v5.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/epoll-use-refcount-to-reduce-ep_mutex-contention-v5.patch

This patch will later appear in the mm-nonmm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Paolo Abeni <pabeni@redhat.com>
Subject: epoll-use-refcount-to-reduce-ep_mutex-contention-v5
Date: Wed, 8 Mar 2023 22:51:31 +0100

update some comments

Link: https://lkml.kernel.org/r/323de732635cc3513c1837c6cbb98f012174f994.1678312201.git.pabeni@redhat.com
Tested-by: Xiumei Mu <xmu@redhiat.com>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Acked-by: Soheil Hassas Yeganeh <soheil@google.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Carlos Maiolino <cmaiolino@redhat.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Eric Biggers <ebiggers@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---


--- a/fs/eventpoll.c~epoll-use-refcount-to-reduce-ep_mutex-contention-v5
+++ a/fs/eventpoll.c
@@ -714,6 +714,8 @@ static void ep_free(struct eventpoll *ep
  * Removes a "struct epitem" from the eventpoll RB tree and deallocates
  * all the associated resources. Must be called with "mtx" held.
  * If the dying flag is set, do the removal only if force is true.
+ * This prevents ep_clear_and_put() from dropping all the ep references
+ * while running concurrently with eventpoll_release_file().
  * Returns true if the eventpoll can be disposed.
  */
 static bool __ep_remove(struct eventpoll *ep, struct epitem *epi, bool force)
@@ -941,14 +943,13 @@ void eventpoll_release_file(struct file
 	bool dispose;
 
 	/*
-	 * Use the 'dying' flag to prevent a concurrent ep_cleat_and_put() from
+	 * Use the 'dying' flag to prevent a concurrent ep_clear_and_put() from
 	 * touching the epitems list before eventpoll_release_file() can access
 	 * the ep->mtx.
 	 */
 again:
 	spin_lock(&file->f_lock);
 	if (file->f_ep && file->f_ep->first) {
-		/* detach from ep tree */
 		epi = hlist_entry(file->f_ep->first, struct epitem, fllink);
 		epi->dying = true;
 		spin_unlock(&file->f_lock);
_

Patches currently in -mm which might be from pabeni@redhat.com are

epoll-use-refcount-to-reduce-ep_mutex-contention.patch
epoll-use-refcount-to-reduce-ep_mutex-contention-v5.patch