linux-kernel - [PATCH 5/9] ext4: prevent stale extent cache entries caused by concurrent get es

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Message-ID: <20250423085257.122685-6-yi.zhang@huaweicloud.com>
Date: Wed, 23 Apr 2025 16:52:53 +0800
From: Zhang Yi <yi.zhang@...weicloud.com>
To: linux-ext4@...r.kernel.org
Cc: linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	tytso@....edu,
	adilger.kernel@...ger.ca,
	jack@...e.cz,
	yi.zhang@...wei.com,
	yi.zhang@...weicloud.com,
	libaokun1@...wei.com,
	yukuai3@...wei.com,
	yangerkun@...wei.com
Subject: [PATCH 5/9] ext4: prevent stale extent cache entries caused by concurrent get es_cache

From: Zhang Yi <yi.zhang@...wei.com>

The EXT4_IOC_GET_ES_CACHE and EXT4_IOC_PRECACHE_EXTENTS currently
invokes ext4_ext_precache() to preload the extent cache without holding
the inode's i_rwsem. This can result in stale extent cache entries when
competing with operations such as ext4_collapse_range() which calls
ext4_ext_remove_space() or ext4_ext_shift_extents().

The problem arises when ext4_ext_remove_space() temporarily releases
i_data_sem due to insufficient journal credits. During this interval, a
concurrent EXT4_IOC_GET_ES_CACHE or EXT4_IOC_PRECACHE_EXTENTS may cache
extent entries that are about to be deleted. As a result, these cached
entries become stale and inconsistent with the actual extents.

Loading the extents cache without holding the inode's i_rwsem or the
mapping's invalidate_lock is not permitted besides during the writeback.
Fix this by holding the i_rwsem during EXT4_IOC_GET_ES_CACHE and
EXT4_IOC_PRECACHE_EXTENTS.

Signed-off-by: Zhang Yi <yi.zhang@...wei.com>
---
 fs/ext4/extents.c | 2 ++
 fs/ext4/ioctl.c   | 8 +++++++-
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index 3adf05fbdd59..b5eb89ef7ae2 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -5011,7 +5011,9 @@ int ext4_get_es_cache(struct inode *inode, struct fiemap_extent_info *fieinfo,
 	}

 	if (fieinfo->fi_flags & FIEMAP_FLAG_CACHE) {
+		inode_lock_shared(inode);
 		error = ext4_ext_precache(inode);
+		inode_unlock_shared(inode);
 		if (error)
 			return error;
 		fieinfo->fi_flags &= ~FIEMAP_FLAG_CACHE;
diff --git a/fs/ext4/ioctl.c b/fs/ext4/ioctl.c
index d17207386ead..0e240013c84d 100644
--- a/fs/ext4/ioctl.c
+++ b/fs/ext4/ioctl.c
@@ -1505,8 +1505,14 @@ static long __ext4_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 		return 0;
 	}
 	case EXT4_IOC_PRECACHE_EXTENTS:
-		return ext4_ext_precache(inode);
+	{
+		int ret;

+		inode_lock_shared(inode);
+		ret = ext4_ext_precache(inode);
+		inode_unlock_shared(inode);
+		return ret;
+	}
 	case FS_IOC_SET_ENCRYPTION_POLICY:
 		if (!ext4_has_feature_encrypt(sb))
 			return -EOPNOTSUPP;
-- 
2.46.1