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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Jan Kara <jack@suse.cz>,
        Theodore Tso <tytso@mit.edu>
Subject: [PATCH 5.19 0120/1157] mbcache: dont reclaim used entries
Date:   Mon, 15 Aug 2022 19:51:16 +0200
Message-Id: <20220815180444.411280397@linuxfoundation.org>
In-Reply-To: <20220815180439.416659447@linuxfoundation.org>
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From: Jan Kara <jack@suse.cz>

commit 58318914186c157477b978b1739dfe2f1b9dc0fe upstream.

Do not reclaim entries that are currently used by somebody from a
shrinker. Firstly, these entries are likely useful. Secondly, we will
need to keep such entries to protect pending increment of xattr block
refcount.

CC: stable@vger.kernel.org
Fixes: 82939d7999df ("ext4: convert to mbcache2")
Signed-off-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20220712105436.32204-1-jack@suse.cz
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 fs/mbcache.c |   10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

--- a/fs/mbcache.c
+++ b/fs/mbcache.c
@@ -288,7 +288,7 @@ static unsigned long mb_cache_shrink(str
 	while (nr_to_scan-- && !list_empty(&cache->c_list)) {
 		entry = list_first_entry(&cache->c_list,
 					 struct mb_cache_entry, e_list);
-		if (entry->e_referenced) {
+		if (entry->e_referenced || atomic_read(&entry->e_refcnt) > 2) {
 			entry->e_referenced = 0;
 			list_move_tail(&entry->e_list, &cache->c_list);
 			continue;
@@ -302,6 +302,14 @@ static unsigned long mb_cache_shrink(str
 		spin_unlock(&cache->c_list_lock);
 		head = mb_cache_entry_head(cache, entry->e_key);
 		hlist_bl_lock(head);
+		/* Now a reliable check if the entry didn't get used... */
+		if (atomic_read(&entry->e_refcnt) > 2) {
+			hlist_bl_unlock(head);
+			spin_lock(&cache->c_list_lock);
+			list_add_tail(&entry->e_list, &cache->c_list);
+			cache->c_entry_count++;
+			continue;
+		}
 		if (!hlist_bl_unhashed(&entry->e_hash_list)) {
 			hlist_bl_del_init(&entry->e_hash_list);
 			atomic_dec(&entry->e_refcnt);