linux-ext4 - [PATCH] ext4: Avoid excessive credit estimate in ext4

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Message-Id: <20240307115320.28949-1-jack@suse.cz>
Date: Thu,  7 Mar 2024 12:53:20 +0100
From: Jan Kara <jack@...e.cz>
To: Ted Tso <tytso@....edu>
Cc: <linux-ext4@...r.kernel.org>,
	Jan Kara <jack@...e.cz>
Subject: [PATCH] ext4: Avoid excessive credit estimate in ext4_tmpfile()

A user with minimum journal size (1024 blocks these days) complained
about the following error triggered by generic/697 test in
ext4_tmpfile():

run fstests generic/697 at 2024-02-28 05:34:46
JBD2: vfstest wants too many credits credits:260 rsv_credits:0 max:256
EXT4-fs error (device loop0) in __ext4_new_inode:1083: error 28

Indeed the credit estimate in ext4_tmpfile() is huge.
EXT4_MAXQUOTAS_INIT_BLOCKS() is 219, then 10 credits from ext4_tmpfile()
itself and then ext4_xattr_credits_for_new_inode() adds more credits
needed for security attributes and ACLs. Now the
EXT4_MAXQUOTAS_INIT_BLOCKS() is in fact unnecessary because we've
already initialized quotas with dquot_init() shortly before and so
EXT4_MAXQUOTAS_TRANS_BLOCKS() is enough (which boils down to 3 credits).

Fixes: af51a2ac36d1 ("ext4: ->tmpfile() support")
Signed-off-by: Jan Kara <jack@...e.cz>
---
 fs/ext4/namei.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
index 05b647e6bc19..58fee3c6febc 100644
--- a/fs/ext4/namei.c
+++ b/fs/ext4/namei.c
@@ -2898,7 +2898,7 @@ static int ext4_tmpfile(struct mnt_idmap *idmap, struct inode *dir,
 	inode = ext4_new_inode_start_handle(idmap, dir, mode,
 					    NULL, 0, NULL,
 					    EXT4_HT_DIR,
-			EXT4_MAXQUOTAS_INIT_BLOCKS(dir->i_sb) +
+			EXT4_MAXQUOTAS_TRANS_BLOCKS(dir->i_sb) +
 			  4 + EXT4_XATTR_TRANS_BLOCKS);
 	handle = ext4_journal_current_handle();
 	err = PTR_ERR(inode);
-- 
2.35.3