linux-kernel - [PATCH] vfs: do not try to evict inode when super is frozen

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Message-Id: <20220304022104.2525009-1-jaegeuk@kernel.org>
Date:   Thu,  3 Mar 2022 18:21:04 -0800
From:   Jaegeuk Kim <jaegeuk@...nel.org>
To:     linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Cc:     Jaegeuk Kim <jaegeuk@...nel.org>
Subject: [PATCH] vfs: do not try to evict inode when super is frozen

Otherwise, we will get a deadlock.

[freeze test]                         shrinkder
freeze_super
 - pwercpu_down_write(SB_FREEZE_FS)
                                       - super_cache_scan
                                         - down_read(&sb->s_umount)
                                           - prune_icache_sb
                                            - dispose_list
                                             - evict
                                              - f2fs_evict_inode
thaw_super
 - down_write(&sb->s_umount);
                                              - __percpu_down_read(SB_FREEZE_FS)

Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>
---
 fs/super.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/fs/super.c b/fs/super.c
index 7af820ba5ad5..f7303d91f874 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -79,6 +79,12 @@ static unsigned long super_cache_scan(struct shrinker *shrink,
 	if (!trylock_super(sb))
 		return SHRINK_STOP;
 
+	/* This prevents inode eviction that requires SB_FREEZE_FS. */
+	if (sb->s_writers.frozen == SB_FREEZE_FS) {
+		up_read(&sb->s_umount);
+		return SHRINK_STOP;
+	}
+
 	if (sb->s_op->nr_cached_objects)
 		fs_objects = sb->s_op->nr_cached_objects(sb, sc);
 
-- 
2.35.1.616.g0bdcbb4464-goog