This is a note to let you know that I've just added the patch titled
fanotify: limit number of event merge attempts
to the 5.10-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
fanotify-limit-number-of-event-merge-attempts.patch
and it can be found in the queue-5.10 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From b8cd0ee8cda68a888a317991c1e918a8cba1a568 Mon Sep 17 00:00:00 2001
From: Amir Goldstein <amir73il@xxxxxxxxx>
Date: Thu, 4 Mar 2021 12:48:26 +0200
Subject: fanotify: limit number of event merge attempts
From: Amir Goldstein <amir73il@xxxxxxxxx>
commit b8cd0ee8cda68a888a317991c1e918a8cba1a568 upstream.
Event merges are expensive when event queue size is large, so limit the
linear search to 128 merge tests.
[Stable backport notes] The following statement from upstream commit is
irrelevant for backport:
-
-In combination with 128 size hash table, there is a potential to merge
-with up to 16K events in the hashed queue.
-
[Stable backport notes] The problem is as old as fanotify and described
in the linked cover letter "Performance improvement for fanotify merge".
This backported patch fixes the performance issue at the cost of merging
fewer potential events. Fixing the performance issue is more important
than preserving the "event merge" behavior, which was not predictable in
any way that applications could rely on.
Link: https://lore.kernel.org/r/20210304104826.3993892-6-amir73il@xxxxxxxxx
Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx>
Signed-off-by: Jan Kara <jack@xxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Link: https://lore.kernel.org/linux-fsdevel/20210202162010.305971-1-amir73il@xxxxxxxxx/
Link: https://lore.kernel.org/linux-fsdevel/20210915163334.GD6166@xxxxxxxxxxxxxx/
Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
fs/notify/fanotify/fanotify.c | 6 ++++++
1 file changed, 6 insertions(+)
--- a/fs/notify/fanotify/fanotify.c
+++ b/fs/notify/fanotify/fanotify.c
@@ -129,11 +129,15 @@ static bool fanotify_should_merge(struct
return false;
}
+/* Limit event merges to limit CPU overhead per event */
+#define FANOTIFY_MAX_MERGE_EVENTS 128
+
/* and the list better be locked by something too! */
static int fanotify_merge(struct list_head *list, struct fsnotify_event *event)
{
struct fsnotify_event *test_event;
struct fanotify_event *new;
+ int i = 0;
pr_debug("%s: list=%p event=%p\n", __func__, list, event);
new = FANOTIFY_E(event);
@@ -147,6 +151,8 @@ static int fanotify_merge(struct list_he
return 0;
list_for_each_entry_reverse(test_event, list, list) {
+ if (++i > FANOTIFY_MAX_MERGE_EVENTS)
+ break;
if (fanotify_should_merge(test_event, event)) {
FANOTIFY_E(test_event)->mask |= new->mask;
return 1;
Patches currently in stable-queue which might be from amir73il@xxxxxxxxx are
queue-5.10/fanotify-limit-number-of-event-merge-attempts.patch
