linux-ext4 - Is there any reason for us to use EXT4_MAXQUOTAS_INIT

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Message-ID: <20150415155537.GA32494@thunk.org>
Date:	Wed, 15 Apr 2015 11:55:37 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	Jan Kara <jack@...e.cz>
Cc:	linux-ext4@...r.kernel.org
Subject: Is there any reason for us to use EXT4_MAXQUOTAS_INIT_BLOCKS?

It looks to me like EXT4_MAXQUOTAS_INIT_BLOCKS includes the credits
neede to set up the quota records.  So if we move the call to
dquot_initialize(inode) outside of the normal transaction (which we
should probably do in all cases), that means that we shouldn't ever
need to use EXT4_MAX_QUOTAS_INIT_BLOCKS.  Is that right?

The reason why I ask is the following is a easy way to trigger a file
system problem:

mke2fs -Fq -t ext4 -b 4096 /dev/vdc 50M
mount -t ext4 -o usrquota,grpquota /dev/vdc
l8=12345678
l16=$l8$l8
l32=$l16$l16
l64=$l32$l32
dmesg -n 7
ln -s $l64 /vdc/link

This will result in:

[    5.229165] JBD2: ln wants too many credits (156 > 128)
[    5.230194] EXT4-fs error (device vdc) in __ext4_new_inode:843: error 28

In other places where we are allocating a new inode (such as mknod),
we're doing the following:

	credits = EXT4_DATA_TRANS_BLOCKS(dir->i_sb) +
			EXT4_INDEX_EXTRA_TRANS_BLOCKS + 3;

Which is 37 blocks, and I suspect that's still too darned much.  But
if we don't need to use EXT4_MAXQUOTAS_INIT_BLOCKS in ext4_mknod(), we
shouldn't be needing it in ext4_symlink(), either.

Am I missing anything?

Thanks,

					- Ted
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