Re: [PATCH] jbd2: move more common code into journal_init_common()

From: Theodore Ts'o
Date: Thu Sep 15 2016 - 15:59:13 EST

On Thu, Sep 15, 2016 at 12:03:09PM -0400, Theodore Ts'o wrote:
> On Wed, Sep 07, 2016 at 03:16:24PM +0200, Jan Kara wrote:
> > On Wed 07-09-16 20:41:13, Geliang Tang wrote:
> > > There are some repetitive code in jbd2_journal_init_dev() and
> > > jbd2_journal_init_inode(). So this patch moves the common code into
> > > journal_init_common() helper to simplify the code. And fix the coding
> > > style warnings reported by checkpatch.pl by the way.
> > >
> > > Signed-off-by: Geliang Tang <geliangtang@xxxxxxxxx>
> >
> > The patch looks good to me. You can add:
> >
> > Reviewed-by: Jan Kara <jack@xxxxxxx>
>
> Applied, thanks.
>

Hi Geiliang,

This patch is causing a WARN_ON:

[ 13.923139] ------------[ cut here ]------------
[ 13.924644] WARNING: CPU: 0 PID: 2534 at /usr/projects/linux/ext4/fs/proc/generic.c:369 __proc_create+0xe1/0x156
[ 13.926751] name len 0
[ 13.927283] Modules linked in:
[ 13.927954] CPU: 0 PID: 2534 Comm: mount Tainted: G W 4.8.0-rc4-00139-g52c4278 #685
[ 13.929809] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Debian-1.8.2-1 04/01/2014
[ 13.931643] 00000000 00000246 f3c1dd3c c13faa3e f3c1dd68 c11cc9c1 f3c1dd54 c1087d00
[ 13.933425] 00000171 f4727b0c f3c1ddac f5183bc0 f3c1dd70 c1087d44 00000009 00000000
[ 13.935199] f3c1dd68 c1969704 f3c1dd84 f3c1dda0 c11cc9c1 c19696d9 00000171 c1969704
[ 13.936987] Call Trace:
[ 13.937507] [<c13faa3e>] dump_stack+0x73/0xa5
[ 13.938438] [<c11cc9c1>] ? __proc_create+0xe1/0x156
[ 13.939503] [<c1087d00>] __warn+0xbc/0xd3
[ 13.940404] [<c1087d44>] warn_slowpath_fmt+0x2d/0x32
[ 13.941470] [<c11cc9c1>] __proc_create+0xe1/0x156
[ 13.942461] [<c11ccc8d>] proc_mkdir_data+0x2c/0x6e
[ 13.943484] [<c11cccf6>] proc_mkdir+0x13/0x15
[ 13.944425] [<c122a597>] journal_init_common+0x1a8/0x26a
[ 13.945539] [<c122a753>] jbd2_journal_init_inode+0xa9/0xfd
[ 13.946702] [<c11fa5cf>] ext4_fill_super+0x18e5/0x2a92
[ 13.947794] [<c1402d01>] ? bitmap_string.isra.6+0xa9/0xc1
[ 13.948926] [<c117ec1f>] mount_bdev+0x114/0x15f
[ 13.950333] [<c11f48c4>] ext4_mount+0x15/0x17
[ 13.951985] [<c11f8cea>] ? ext4_calculate_overhead+0x30e/0x30e
[ 13.954172] [<c117f49d>] mount_fs+0x58/0x115
[ 13.955789] [<c11943cb>] vfs_kern_mount+0x4c/0xae
[ 13.957588] [<c11966dc>] do_mount+0x6b0/0x8d7
[ 13.959270] [<c1405620>] ? _copy_from_user+0x44/0x57
[ 13.961140] [<c1150873>] ? strndup_user+0x31/0x42
[ 13.962919] [<c1196aab>] SyS_mount+0x57/0x7b
[ 13.964609] [<c10015b2>] do_int80_syscall_32+0x4d/0x5f
[ 13.966555] [<c16f6ccb>] entry_INT80_32+0x2f/0x2f
[ 13.968402] ---[ end trace 2eb7cc6d9a94f309 ]---
[ 14.017482] EXT4-fs (vdc): mounted filesystem with ordered data mode. Opts: (null)

The problem is that journal->j_devname isn't initialized until *after*
journal_init_common(), and it's used by jbd2_stats_proc_init(), which
is called by journal_init_common().

To fix it I applied the following fix on top of your patch.

- Ted

diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
index 07e14ef..927da49 100644
--- a/fs/jbd2/journal.c
+++ b/fs/jbd2/journal.c
@@ -1141,13 +1141,11 @@ static journal_t *journal_init_common(struct block_device *bdev,
journal->j_fs_dev = fs_dev;
journal->j_blk_offset = start;
journal->j_maxlen = len;
- jbd2_stats_proc_init(journal);
n = journal->j_blocksize / sizeof(journal_block_tag_t);
journal->j_wbufsize = n;
journal->j_wbuf = kmalloc_array(n, sizeof(struct buffer_head *),
GFP_KERNEL);
if (!journal->j_wbuf) {
- jbd2_stats_proc_exit(journal);
kfree(journal);
return NULL;
}
@@ -1157,7 +1155,6 @@ static journal_t *journal_init_common(struct block_device *bdev,
pr_err("%s: Cannot get buffer for journal superblock\n",
__func__);
kfree(journal->j_wbuf);
- jbd2_stats_proc_exit(journal);
kfree(journal);
return NULL;
}
@@ -1202,6 +1199,7 @@ journal_t *jbd2_journal_init_dev(struct block_device *bdev,

bdevname(journal->j_dev, journal->j_devname);
strreplace(journal->j_devname, '/', '!');
+ jbd2_stats_proc_init(journal);

return journal;
}
@@ -1241,6 +1239,7 @@ journal_t *jbd2_journal_init_inode(struct inode *inode)
bdevname(journal->j_dev, journal->j_devname);
p = strreplace(journal->j_devname, '/', '!');
sprintf(p, "-%lu", journal->j_inode->i_ino);
+ jbd2_stats_proc_init(journal);

return journal;
}