linux-kernel - Re: [PATCH] ext4: cache es->s_journal_inum in ext4_sb

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Message-ID: <Z-Lunpbeh176mwRu@li-dc0c254c-257c-11b2-a85c-98b6c1322444.ibm.com>
Date: Tue, 25 Mar 2025 23:27:50 +0530
From: Ojaswin Mujoo <ojaswin@...ux.ibm.com>
To: "Theodore Ts'o" <tytso@....edu>
Cc: linux-ext4@...r.kernel.org, Jan Kara <jack@...e.cz>,
        Baokun Li <libaokun1@...wei.com>,
        Ritesh Harjani <ritesh.list@...il.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ext4: cache es->s_journal_inum in ext4_sb_info

On Tue, Mar 18, 2025 at 10:31:29PM -0400, Theodore Ts'o wrote:
> On Tue, Mar 18, 2025 at 01:42:31PM +0530, Ojaswin Mujoo wrote:
> > > So this is something we need to do if the journal is actived, and if
> > > it's active, then sbi->s_journal will be non-NULL, and so we can just
> > > check to see if inode == sbi->s_journal instead.  This will simplify
> > 
> > I believe you mean inode == sbi->s_journal->j_inode here right?
> 
> Yes, that's what I meant; sorry for the not catching this before I
> sent my reply.
> 
> Cheers,
> 
> 					- Ted

Hi Ted, Baokun,

I got some time to revisit this. Seems like checking against
s_journal->j_inode is not enough. This is because both
ext4_check_blockref() and check_block_validity() can be called even
before journal->j_inode is set:

ext4_open_inode_journal
  ext4_get_journal_inode
	  __ext4_iget
		  ext4_ind_check_inode
			  ext4_check_blockref  /* j_inode not set */

  journal = jbd2_journal_init_inode
	  bmap
		  ext4_bmap
			 iomap_bmap
			   ext4_iomap_begin
				   ext4_map_blocks
					   check_block_validity

  journal->j_inode = inode


Now, I think in this case the best solution might be to use the extra
field like we do in this patch but set  EXT4_SB(sb)->s_journal_ino
sufficiently early.

Thoughts?