linux-ext4 - [PATCH v2 3/3] ext4: do not update s_last

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Message-Id: <1524445859-26970-4-git-send-email-amir73il@gmail.com>
Date:   Sun, 22 Apr 2018 18:10:59 -0700
From:   Amir Goldstein <amir73il@...il.com>
To:     Theodore Tso <tytso@....edu>
Cc:     Jan Kara <jack@...e.cz>, linux-ext4@...r.kernel.org
Subject: [PATCH v2 3/3] ext4: do not update s_last_mounted of a frozen fs

If fs is frozen after mount and before the first file open, the
update of s_last_mounted bypasses freeze protection and prints out
a WARNING splat:

$ mount /vdf
$ fsfreeze -f /vdf
$ cat /vdf/foo

[   31.578555] WARNING: CPU: 1 PID: 1415 at
fs/ext4/ext4_jbd2.c:53 ext4_journal_check_start+0x48/0x82

[   31.614016] Call Trace:
[   31.614997]  __ext4_journal_start_sb+0xe4/0x1a4
[   31.616771]  ? ext4_file_open+0xb6/0x189
[   31.618094]  ext4_file_open+0xb6/0x189

If fs is frozen, skip s_last_mounted update.

[backport hint: to apply to stable tree, need to apply also patches
 vfs: add the sb_start_intwrite_trylock() helper
 ext4: factor out helper ext4_sample_last_mounted()]

Fixes: bc0b0d6d69ee ("ext4: update the s_last_mounted field in the
superblock")
Cc: <stable@...r.kernel.org>
Signed-off-by: Amir Goldstein <amir73il@...il.com>
---
 fs/ext4/file.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/fs/ext4/file.c b/fs/ext4/file.c
index 065e95bb7186..f097a76ee54e 100644
--- a/fs/ext4/file.c
+++ b/fs/ext4/file.c
@@ -392,7 +392,7 @@ static int ext4_sample_last_mounted(struct super_block *sb,
 	if (likely(sbi->s_mount_flags & EXT4_MF_MNTDIR_SAMPLED))
 		return 0;
 
-	if (sb_rdonly(sb))
+	if (sb_rdonly(sb) || !sb_start_intwrite_trylock(sb))
 		return 0;
 
 	sbi->s_mount_flags |= EXT4_MF_MNTDIR_SAMPLED;
@@ -406,12 +406,14 @@ static int ext4_sample_last_mounted(struct super_block *sb,
 	path.mnt = mnt;
 	path.dentry = mnt->mnt_root;
 	cp = d_path(&path, buf, sizeof(buf));
+	err = 0;
 	if (IS_ERR(cp))
-		return 0;
+		goto out_intwrite;
 
 	handle = ext4_journal_start_sb(sb, EXT4_HT_MISC, 1);
+	err = PTR_ERR(handle);
 	if (IS_ERR(handle))
-		return PTR_ERR(handle);
+		goto out_intwrite;
 	BUFFER_TRACE(sbi->s_sbh, "get_write_access");
 	err = ext4_journal_get_write_access(handle, sbi->s_sbh);
 	if (err)
@@ -421,6 +423,8 @@ static int ext4_sample_last_mounted(struct super_block *sb,
 	ext4_handle_dirty_super(handle, sb);
 out:
 	ext4_journal_stop(handle);
+out_intwrite:
+	sb_end_intwrite(sb);
 	return err;
 }
 
-- 
2.7.4